From d074f1c514cadced4f7414ef54325f76ff258529 Mon Sep 17 00:00:00 2001
From: Justin Ridgewell <jridgewell@google.com>
Date: Thu, 4 Jul 2019 01:01:46 -0400
Subject: [PATCH 01/17] Distinguish between a ExistingRawSourceMap and
 ExistingDecodedSourceMap

---
 src/Chunk.ts                     | 10 ++++++++--
 src/Module.ts                    |  8 ++++----
 src/rollup/types.d.ts            | 27 ++++++++++++++++++---------
 src/utils/collapseSourcemaps.ts  | 10 ++++------
 src/utils/getOriginalLocation.ts |  8 ++++----
 src/utils/renderChunk.ts         | 17 ++++++++++++-----
 src/utils/transform.ts           | 12 ++++--------
 typings/declarations.d.ts        |  4 +++-
 8 files changed, 57 insertions(+), 39 deletions(-)

diff --git a/src/Chunk.ts b/src/Chunk.ts
index c64bd6e1fd1..493ec35b8b1 100644
--- a/src/Chunk.ts
+++ b/src/Chunk.ts
@@ -14,7 +14,13 @@ import ExternalModule from './ExternalModule';
 import finalisers from './finalisers/index';
 import Graph from './Graph';
 import Module from './Module';
-import { GlobalsOption, OutputOptions, RawSourceMap, RenderedChunk, RenderedModule } from './rollup/types';
+import {
+	ExistingRawSourceMap,
+	GlobalsOption,
+	OutputOptions,
+	RenderedChunk,
+	RenderedModule
+} from './rollup/types';
 import { Addons } from './utils/addons';
 import { toBase64 } from './utils/base64';
 import collapseSourcemaps from './utils/collapseSourcemaps';
@@ -676,7 +682,7 @@ export default class Chunk {
 		timeEnd('render format', 3);
 
 		let map: SourceMap = null as any;
-		const chunkSourcemapChain: RawSourceMap[] = [];
+		const chunkSourcemapChain: ExistingRawSourceMap[] = [];
 
 		return renderChunk({
 			chunk: this,
diff --git a/src/Module.ts b/src/Module.ts
index acf5541094d..63d12235c4b 100644
--- a/src/Module.ts
+++ b/src/Module.ts
@@ -33,8 +33,8 @@ import Graph from './Graph';
 import {
 	Asset,
 	EmittedChunk,
+	ExistingRawSourceMap,
 	ModuleJSON,
-	RawSourceMap,
 	ResolvedIdMap,
 	RollupError,
 	RollupWarning,
@@ -199,11 +199,11 @@ export default class Module {
 	manualChunkAlias: string = null as any;
 	moduleSideEffects: boolean;
 	originalCode!: string;
-	originalSourcemap!: RawSourceMap | null;
+	originalSourcemap!: ExistingRawSourceMap | null;
 	reexports: { [name: string]: ReexportDescription } = Object.create(null);
 	resolvedIds!: ResolvedIdMap;
 	scope!: ModuleScope;
-	sourcemapChain!: RawSourceMap[];
+	sourcemapChain!: ExistingRawSourceMap[];
 	sources: string[] = [];
 	transformAssets?: Asset[];
 	transformChunks?: EmittedChunk[];
@@ -540,7 +540,7 @@ export default class Module {
 		this.code = code;
 		this.originalCode = originalCode;
 		this.originalSourcemap = originalSourcemap;
-		this.sourcemapChain = sourcemapChain as RawSourceMap[];
+		this.sourcemapChain = sourcemapChain;
 		if (transformAssets) {
 			this.transformAssets = transformAssets;
 		}
diff --git a/src/rollup/types.d.ts b/src/rollup/types.d.ts
index f4c84280b70..6a06894475b 100644
--- a/src/rollup/types.d.ts
+++ b/src/rollup/types.d.ts
@@ -38,6 +38,16 @@ export interface RollupLogProps {
 	url?: string;
 }
 
+export interface ExistingDecodedSourceMap {
+	file?: string;
+	mappings: number[][][];
+	names: string[];
+	sourceRoot?: string;
+	sources: string[];
+	sourcesContent?: string[];
+	version: number;
+}
+
 export interface ExistingRawSourceMap {
 	file?: string;
 	mappings: string;
@@ -48,8 +58,6 @@ export interface ExistingRawSourceMap {
 	version: number;
 }
 
-export type RawSourceMap = { mappings: '' } | ExistingRawSourceMap;
-
 export interface SourceMap {
 	file: string;
 	mappings: string;
@@ -64,7 +72,7 @@ export interface SourceMap {
 export interface SourceDescription {
 	ast?: ESTree.Program;
 	code: string;
-	map?: string | RawSourceMap;
+	map?: string | ExistingRawSourceMap;
 	moduleSideEffects?: boolean | null;
 }
 
@@ -79,9 +87,10 @@ export interface TransformModuleJSON {
 	customTransformCache: boolean;
 	moduleSideEffects: boolean | null;
 	originalCode: string;
-	originalSourcemap: RawSourceMap | null;
+	originalSourcemap: ExistingDecodedSourceMap | null;
 	resolvedIds?: ResolvedIdMap;
-	sourcemapChain: (RawSourceMap | { missing: true; plugin: string })[];
+	// TODO
+	sourcemapChain: (ExistingDecodedSourceMap | { missing: true; plugin: string })[];
 	transformDependencies: string[] | null;
 }
 
@@ -207,8 +216,8 @@ export type TransformChunkHook = (
 	code: string,
 	options: OutputOptions
 ) =>
-	| Promise<{ code: string; map: RawSourceMap } | null | undefined>
-	| { code: string; map: RawSourceMap }
+	| Promise<{ code: string; map: ExistingRawSourceMap } | null | undefined>
+	| { code: string; map: ExistingRawSourceMap }
 	| null
 	| undefined;
 
@@ -218,8 +227,8 @@ export type RenderChunkHook = (
 	chunk: RenderedChunk,
 	options: OutputOptions
 ) =>
-	| Promise<{ code: string; map: RawSourceMap } | null>
-	| { code: string; map: RawSourceMap }
+	| Promise<{ code: string; map: ExistingRawSourceMap } | null>
+	| { code: string; map: ExistingRawSourceMap }
 	| string
 	| null;
 
diff --git a/src/utils/collapseSourcemaps.ts b/src/utils/collapseSourcemaps.ts
index dfde40ddc7c..9c7d683e61f 100644
--- a/src/utils/collapseSourcemaps.ts
+++ b/src/utils/collapseSourcemaps.ts
@@ -1,7 +1,7 @@
 import { DecodedSourceMap, SourceMap } from 'magic-string';
 import Chunk from '../Chunk';
 import Module from '../Module';
-import { ExistingRawSourceMap, RawSourceMap } from '../rollup/types';
+import { ExistingRawSourceMap, ExistingRawSourceMap } from '../rollup/types';
 import { error } from './error';
 import { basename, dirname, relative, resolve } from './path';
 
@@ -77,9 +77,7 @@ class Link {
 						sourcesContent[sourceIndex] !== traced.source.content
 					) {
 						error({
-							message: `Multiple conflicting contents for sourcemap source ${
-								traced.source.filename
-							}`
+							message: `Multiple conflicting contents for sourcemap source ${traced.source.filename}`
 						});
 					}
 
@@ -148,7 +146,7 @@ export default function collapseSourcemaps(
 	file: string,
 	map: DecodedSourceMap,
 	modules: Module[],
-	bundleSourcemapChain: RawSourceMap[],
+	bundleSourcemapChain: ExistingRawSourceMap[],
 	excludeContent: boolean
 ) {
 	function linkMap(source: Source, map: any) {
@@ -186,7 +184,7 @@ export default function collapseSourcemaps(
 
 				if (sources == null || (sources.length <= 1 && sources[0] == null)) {
 					source = new Source(module.id, sourcesContent[0]);
-					sourcemapChain = [originalSourcemap as RawSourceMap].concat(sourcemapChain);
+					sourcemapChain = [originalSourcemap].concat(sourcemapChain);
 				} else {
 					// TODO indiscriminately treating IDs and sources as normal paths is probably bad.
 					const directory = dirname(module.id) || '.';
diff --git a/src/utils/getOriginalLocation.ts b/src/utils/getOriginalLocation.ts
index 358cc70a3ab..39c41576dd3 100644
--- a/src/utils/getOriginalLocation.ts
+++ b/src/utils/getOriginalLocation.ts
@@ -1,13 +1,13 @@
-import { ExistingRawSourceMap, RawSourceMap } from '../rollup/types';
+import { ExistingRawSourceMap, ExistingRawSourceMap } from '../rollup/types';
 
 export function getOriginalLocation(
-	sourcemapChain: RawSourceMap[],
+	sourcemapChain: ExistingRawSourceMap[],
 	location: { column: number; line: number; name?: string; source?: string }
 ) {
-	const filteredSourcemapChain = sourcemapChain.filter(sourcemap => sourcemap.mappings);
+	const filteredSourcemapChain = sourcemapChain.filter(sourcemap => sourcemap.mappings.length);
 
 	while (filteredSourcemapChain.length > 0) {
-		const sourcemap = filteredSourcemapChain.pop() as ExistingRawSourceMap;
+		const sourcemap = filteredSourcemapChain.pop();
 		const line: any = sourcemap.mappings[location.line - 1];
 		let locationFound = false;
 
diff --git a/src/utils/renderChunk.ts b/src/utils/renderChunk.ts
index 74c3511a3ee..4dad769f395 100644
--- a/src/utils/renderChunk.ts
+++ b/src/utils/renderChunk.ts
@@ -1,7 +1,7 @@
 import { decode } from 'sourcemap-codec';
 import Chunk from '../Chunk';
 import Graph from '../Graph';
-import { OutputOptions, Plugin, RawSourceMap, RenderedChunk } from '../rollup/types';
+import { ExistingRawSourceMap, OutputOptions, Plugin, RenderedChunk } from '../rollup/types';
 import { error } from './error';
 
 export default function renderChunk({
@@ -17,9 +17,13 @@ export default function renderChunk({
 	graph: Graph;
 	options: OutputOptions;
 	renderChunk: RenderedChunk;
-	sourcemapChain: RawSourceMap[];
+	sourcemapChain: ExistingRawSourceMap[];
 }): Promise<string> {
-	const renderChunkReducer = (code: string, result: any, plugin: Plugin): string => {
+	const renderChunkReducer = (
+		code: string,
+		result: { code: string; map?: ExistingRawSourceMap | string },
+		plugin: Plugin
+	): string => {
 		if (result == null) return code;
 
 		if (typeof result === 'string')
@@ -28,11 +32,14 @@ export default function renderChunk({
 				map: undefined
 			};
 
-		const map = typeof result.map === 'string' ? JSON.parse(result.map) : result.map;
+		const map =
+			typeof result.map === 'string'
+				? (JSON.parse(result.map) as ExistingRawSourceMap)
+				: result.map || null;
 		if (map && typeof map.mappings === 'string') map.mappings = decode(map.mappings);
 
 		// strict null check allows 'null' maps to not be pushed to the chain, while 'undefined' gets the missing map warning
-		if (map !== null) sourcemapChain.push(map || { missing: true, plugin: plugin.name });
+		sourcemapChain.push(map || { missing: true, plugin: plugin.name });
 
 		return result.code;
 	};
diff --git a/src/utils/transform.ts b/src/utils/transform.ts
index 05fc9123202..4ec4a75d37a 100644
--- a/src/utils/transform.ts
+++ b/src/utils/transform.ts
@@ -9,7 +9,6 @@ import {
 	Plugin,
 	PluginCache,
 	PluginContext,
-	RawSourceMap,
 	RollupError,
 	RollupWarning,
 	TransformModuleJSON,
@@ -27,9 +26,10 @@ export default function transform(
 	module: Module
 ): Promise<TransformModuleJSON> {
 	const id = module.id;
-	const sourcemapChain: (RawSourceMap | { missing: true; plugin: string })[] = [];
+	const sourcemapChain: (ExistingRawSourceMap | { missing: true; plugin: string })[] = [];
 
-	const originalSourcemap = typeof source.map === 'string' ? JSON.parse(source.map) : source.map;
+	const originalSourcemap =
+		typeof source.map === 'string' ? (JSON.parse(source.map) as ExistingRawSourceMap) : source.map;
 	if (originalSourcemap && typeof originalSourcemap.mappings === 'string')
 		originalSourcemap.mappings = decode(originalSourcemap.mappings);
 
@@ -103,11 +103,7 @@ export default function transform(
 		}
 
 		// strict null check allows 'null' maps to not be pushed to the chain, while 'undefined' gets the missing map warning
-		if (result.map !== null) {
-			sourcemapChain.push(
-				(result.map as ExistingRawSourceMap) || { missing: true, plugin: plugin.name }
-			);
-		}
+		sourcemapChain.push(result.map || { missing: true, plugin: plugin.name });
 
 		ast = result.ast;
 
diff --git a/typings/declarations.d.ts b/typings/declarations.d.ts
index 71f65898dd6..5a94638f7ee 100644
--- a/typings/declarations.d.ts
+++ b/typings/declarations.d.ts
@@ -12,7 +12,9 @@ declare module 'signal-exit';
 declare module 'date-time';
 declare module 'locate-character';
 declare module 'is-reference';
-declare module 'sourcemap-codec';
+declare module 'sourcemap-codec' {
+	export function decode(mappings: string): number[][][];
+}
 declare module 'require-relative';
 declare module 'acorn-dynamic-import';
 declare module 'acorn-import-meta';

From c3298494b8d2d1bb2f1558c8f4bf966dfff2c46d Mon Sep 17 00:00:00 2001
From: Justin Ridgewell <jridgewell@google.com>
Date: Thu, 4 Jul 2019 01:23:26 -0400
Subject: [PATCH 02/17] Start work on DecodedSourceMapOrMissing type

---
 src/Chunk.ts                     |  4 ++--
 src/Module.ts                    |  8 +++++---
 src/rollup/types.d.ts            | 12 ++++++++++--
 src/utils/collapseSourcemaps.ts  |  5 +++--
 src/utils/getOriginalLocation.ts | 11 +++++++----
 src/utils/renderChunk.ts         | 10 ++++++++--
 src/utils/transform.ts           |  3 ++-
 7 files changed, 37 insertions(+), 16 deletions(-)

diff --git a/src/Chunk.ts b/src/Chunk.ts
index 493ec35b8b1..04e3b0683f0 100644
--- a/src/Chunk.ts
+++ b/src/Chunk.ts
@@ -15,7 +15,7 @@ import finalisers from './finalisers/index';
 import Graph from './Graph';
 import Module from './Module';
 import {
-	ExistingRawSourceMap,
+	DecodedSourceMapOrMissing,
 	GlobalsOption,
 	OutputOptions,
 	RenderedChunk,
@@ -682,7 +682,7 @@ export default class Chunk {
 		timeEnd('render format', 3);
 
 		let map: SourceMap = null as any;
-		const chunkSourcemapChain: ExistingRawSourceMap[] = [];
+		const chunkSourcemapChain: DecodedSourceMapOrMissing[] = [];
 
 		return renderChunk({
 			chunk: this,
diff --git a/src/Module.ts b/src/Module.ts
index 63d12235c4b..1d272f7162c 100644
--- a/src/Module.ts
+++ b/src/Module.ts
@@ -32,8 +32,9 @@ import ExternalModule from './ExternalModule';
 import Graph from './Graph';
 import {
 	Asset,
+	DecodedSourceMapOrMissing,
 	EmittedChunk,
-	ExistingRawSourceMap,
+	ExistingDecodedSourceMap,
 	ModuleJSON,
 	ResolvedIdMap,
 	RollupError,
@@ -199,11 +200,12 @@ export default class Module {
 	manualChunkAlias: string = null as any;
 	moduleSideEffects: boolean;
 	originalCode!: string;
-	originalSourcemap!: ExistingRawSourceMap | null;
+	originalSourcemap!: ExistingDecodedSourceMap | null;
 	reexports: { [name: string]: ReexportDescription } = Object.create(null);
 	resolvedIds!: ResolvedIdMap;
 	scope!: ModuleScope;
-	sourcemapChain!: ExistingRawSourceMap[];
+	// TODO(jridgewell)
+	sourcemapChain!: DecodedSourceMapOrMissing[];
 	sources: string[] = [];
 	transformAssets?: Asset[];
 	transformChunks?: EmittedChunk[];
diff --git a/src/rollup/types.d.ts b/src/rollup/types.d.ts
index 6a06894475b..b90c3bb6df4 100644
--- a/src/rollup/types.d.ts
+++ b/src/rollup/types.d.ts
@@ -58,6 +58,14 @@ export interface ExistingRawSourceMap {
 	version: number;
 }
 
+export type DecodedSourceMapOrMissing =
+	| {
+			mappings?: never;
+			missing: true;
+			plugin: string;
+	  }
+	| ExistingDecodedSourceMap;
+
 export interface SourceMap {
 	file: string;
 	mappings: string;
@@ -89,8 +97,8 @@ export interface TransformModuleJSON {
 	originalCode: string;
 	originalSourcemap: ExistingDecodedSourceMap | null;
 	resolvedIds?: ResolvedIdMap;
-	// TODO
-	sourcemapChain: (ExistingDecodedSourceMap | { missing: true; plugin: string })[];
+	// TODO(jridewell)
+	sourcemapChain: DecodedSourceMapOrMissing[];
 	transformDependencies: string[] | null;
 }
 
diff --git a/src/utils/collapseSourcemaps.ts b/src/utils/collapseSourcemaps.ts
index 9c7d683e61f..d492ad35f53 100644
--- a/src/utils/collapseSourcemaps.ts
+++ b/src/utils/collapseSourcemaps.ts
@@ -1,7 +1,7 @@
 import { DecodedSourceMap, SourceMap } from 'magic-string';
 import Chunk from '../Chunk';
 import Module from '../Module';
-import { ExistingRawSourceMap, ExistingRawSourceMap } from '../rollup/types';
+import { DecodedSourceMapOrMissing, ExistingRawSourceMap } from '../rollup/types';
 import { error } from './error';
 import { basename, dirname, relative, resolve } from './path';
 
@@ -146,10 +146,11 @@ export default function collapseSourcemaps(
 	file: string,
 	map: DecodedSourceMap,
 	modules: Module[],
-	bundleSourcemapChain: ExistingRawSourceMap[],
+	bundleSourcemapChain: DecodedSourceMapOrMissing[],
 	excludeContent: boolean
 ) {
 	function linkMap(source: Source, map: any) {
+		// TODO(jridgewell): missing
 		if (map.missing) {
 			bundle.graph.warn({
 				code: 'SOURCEMAP_BROKEN',
diff --git a/src/utils/getOriginalLocation.ts b/src/utils/getOriginalLocation.ts
index 39c41576dd3..0a84fe71184 100644
--- a/src/utils/getOriginalLocation.ts
+++ b/src/utils/getOriginalLocation.ts
@@ -1,13 +1,16 @@
-import { ExistingRawSourceMap, ExistingRawSourceMap } from '../rollup/types';
+import { DecodedSourceMapOrMissing, ExistingDecodedSourceMap } from '../rollup/types';
 
 export function getOriginalLocation(
-	sourcemapChain: ExistingRawSourceMap[],
+	sourcemapChain: DecodedSourceMapOrMissing[],
 	location: { column: number; line: number; name?: string; source?: string }
 ) {
-	const filteredSourcemapChain = sourcemapChain.filter(sourcemap => sourcemap.mappings.length);
+	// This cast is guaranteed. If it were a missing Map, it wouldn't have a mappings.
+	const filteredSourcemapChain = sourcemapChain.filter(
+		sourcemap => sourcemap.mappings
+	) as ExistingDecodedSourceMap[];
 
 	while (filteredSourcemapChain.length > 0) {
-		const sourcemap = filteredSourcemapChain.pop();
+		const sourcemap = filteredSourcemapChain.pop()!;
 		const line: any = sourcemap.mappings[location.line - 1];
 		let locationFound = false;
 
diff --git a/src/utils/renderChunk.ts b/src/utils/renderChunk.ts
index 4dad769f395..15d44886188 100644
--- a/src/utils/renderChunk.ts
+++ b/src/utils/renderChunk.ts
@@ -1,7 +1,13 @@
 import { decode } from 'sourcemap-codec';
 import Chunk from '../Chunk';
 import Graph from '../Graph';
-import { ExistingRawSourceMap, OutputOptions, Plugin, RenderedChunk } from '../rollup/types';
+import {
+	DecodedSourceMapOrMissing,
+	ExistingRawSourceMap,
+	OutputOptions,
+	Plugin,
+	RenderedChunk
+} from '../rollup/types';
 import { error } from './error';
 
 export default function renderChunk({
@@ -17,7 +23,7 @@ export default function renderChunk({
 	graph: Graph;
 	options: OutputOptions;
 	renderChunk: RenderedChunk;
-	sourcemapChain: ExistingRawSourceMap[];
+	sourcemapChain: DecodedSourceMapOrMissing[];
 }): Promise<string> {
 	const renderChunkReducer = (
 		code: string,
diff --git a/src/utils/transform.ts b/src/utils/transform.ts
index 4ec4a75d37a..fd2a0ce0d85 100644
--- a/src/utils/transform.ts
+++ b/src/utils/transform.ts
@@ -3,6 +3,7 @@ import Graph from '../Graph';
 import Module from '../Module';
 import {
 	Asset,
+	DecodedSourceMapOrMissing,
 	EmitAsset,
 	EmittedChunk,
 	ExistingRawSourceMap,
@@ -26,7 +27,7 @@ export default function transform(
 	module: Module
 ): Promise<TransformModuleJSON> {
 	const id = module.id;
-	const sourcemapChain: (ExistingRawSourceMap | { missing: true; plugin: string })[] = [];
+	const sourcemapChain: DecodedSourceMapOrMissing[] = [];
 
 	const originalSourcemap =
 		typeof source.map === 'string' ? (JSON.parse(source.map) as ExistingRawSourceMap) : source.map;

From ad2671e0003f73902f099da9bc66e3e8a57d4d95 Mon Sep 17 00:00:00 2001
From: Justin Ridgewell <jridgewell@google.com>
Date: Thu, 4 Jul 2019 01:37:33 -0400
Subject: [PATCH 03/17] Add decodedSourcemap helper

---
 src/rollup/types.d.ts         |  8 ++++----
 src/utils/decodedSourcemap.ts | 21 +++++++++++++++++++++
 src/utils/renderChunk.ts      |  9 ++-------
 src/utils/transform.ts        | 17 ++++-------------
 4 files changed, 31 insertions(+), 24 deletions(-)
 create mode 100644 src/utils/decodedSourcemap.ts

diff --git a/src/rollup/types.d.ts b/src/rollup/types.d.ts
index b90c3bb6df4..da007f5dd86 100644
--- a/src/rollup/types.d.ts
+++ b/src/rollup/types.d.ts
@@ -224,8 +224,8 @@ export type TransformChunkHook = (
 	code: string,
 	options: OutputOptions
 ) =>
-	| Promise<{ code: string; map: ExistingRawSourceMap } | null | undefined>
-	| { code: string; map: ExistingRawSourceMap }
+	| Promise<{ code: string; map?: ExistingRawSourceMap | string } | null | undefined>
+	| { code: string; map?: ExistingRawSourceMap | string }
 	| null
 	| undefined;
 
@@ -235,8 +235,8 @@ export type RenderChunkHook = (
 	chunk: RenderedChunk,
 	options: OutputOptions
 ) =>
-	| Promise<{ code: string; map: ExistingRawSourceMap } | null>
-	| { code: string; map: ExistingRawSourceMap }
+	| Promise<{ code: string; map?: ExistingRawSourceMap | string } | null>
+	| { code: string; map?: ExistingRawSourceMap | string }
 	| string
 	| null;
 
diff --git a/src/utils/decodedSourcemap.ts b/src/utils/decodedSourcemap.ts
new file mode 100644
index 00000000000..3b9316695d8
--- /dev/null
+++ b/src/utils/decodedSourcemap.ts
@@ -0,0 +1,21 @@
+import { decode } from 'sourcemap-codec';
+import { ExistingDecodedSourceMap, ExistingRawSourceMap } from '../rollup/types';
+
+type Input = ExistingRawSourceMap | ExistingDecodedSourceMap | string | undefined;
+
+export function decodedSourcemap(map: Input): ExistingDecodedSourceMap | null {
+	if (!map) return null;
+
+	if (typeof map === 'string') {
+		map = JSON.parse(map) as ExistingRawSourceMap;
+	}
+
+	let mappings: number[][][];
+	if (typeof map.mappings === 'string') {
+		mappings = decode(map.mappings);
+	} else {
+		mappings = map.mappings;
+	}
+
+	return { ...map, mappings };
+}
diff --git a/src/utils/renderChunk.ts b/src/utils/renderChunk.ts
index 15d44886188..3b23060d5a7 100644
--- a/src/utils/renderChunk.ts
+++ b/src/utils/renderChunk.ts
@@ -8,6 +8,7 @@ import {
 	Plugin,
 	RenderedChunk
 } from '../rollup/types';
+import { decodedSourcemap } from './decodedSourcemap';
 import { error } from './error';
 
 export default function renderChunk({
@@ -38,13 +39,7 @@ export default function renderChunk({
 				map: undefined
 			};
 
-		const map =
-			typeof result.map === 'string'
-				? (JSON.parse(result.map) as ExistingRawSourceMap)
-				: result.map || null;
-		if (map && typeof map.mappings === 'string') map.mappings = decode(map.mappings);
-
-		// strict null check allows 'null' maps to not be pushed to the chain, while 'undefined' gets the missing map warning
+		const map = decodedSourcemap(result.map);
 		sourcemapChain.push(map || { missing: true, plugin: plugin.name });
 
 		return result.code;
diff --git a/src/utils/transform.ts b/src/utils/transform.ts
index fd2a0ce0d85..a13000d12b1 100644
--- a/src/utils/transform.ts
+++ b/src/utils/transform.ts
@@ -17,6 +17,7 @@ import {
 	TransformSourceDescription
 } from '../rollup/types';
 import { createTransformEmitAsset } from './assetHooks';
+import { decodedSourcemap } from './decodedSourcemap';
 import { augmentCodeLocation, error } from './error';
 import { dirname, resolve } from './path';
 import { trackPluginCache } from './pluginDriver';
@@ -29,11 +30,7 @@ export default function transform(
 	const id = module.id;
 	const sourcemapChain: DecodedSourceMapOrMissing[] = [];
 
-	const originalSourcemap =
-		typeof source.map === 'string' ? (JSON.parse(source.map) as ExistingRawSourceMap) : source.map;
-	if (originalSourcemap && typeof originalSourcemap.mappings === 'string')
-		originalSourcemap.mappings = decode(originalSourcemap.mappings);
-
+	const originalSourcemap = decodedSourcemap(source.map);
 	const baseEmitAsset = graph.pluginDriver.emitAsset;
 	const originalCode = source.code;
 	let ast = source.ast;
@@ -97,14 +94,8 @@ export default function transform(
 			return code;
 		}
 
-		if (result.map && typeof (result.map as ExistingRawSourceMap).mappings === 'string') {
-			(result.map as ExistingRawSourceMap).mappings = decode(
-				(result.map as ExistingRawSourceMap).mappings
-			);
-		}
-
-		// strict null check allows 'null' maps to not be pushed to the chain, while 'undefined' gets the missing map warning
-		sourcemapChain.push(result.map || { missing: true, plugin: plugin.name });
+		const map = decodedSourcemap(result.map);
+		sourcemapChain.push(map || { missing: true, plugin: plugin.name });
 
 		ast = result.ast;
 

From 9d54e5ccc3edfa342f0759e00d677a3aa6ba5e1c Mon Sep 17 00:00:00 2001
From: Justin Ridgewell <jridgewell@google.com>
Date: Thu, 4 Jul 2019 01:42:58 -0400
Subject: [PATCH 04/17] Fix collapseSourcemaps types

---
 src/utils/collapseSourcemaps.ts | 25 +++++++++----------------
 1 file changed, 9 insertions(+), 16 deletions(-)

diff --git a/src/utils/collapseSourcemaps.ts b/src/utils/collapseSourcemaps.ts
index d492ad35f53..d84befd5e24 100644
--- a/src/utils/collapseSourcemaps.ts
+++ b/src/utils/collapseSourcemaps.ts
@@ -173,33 +173,26 @@ export default function collapseSourcemaps(
 	const moduleSources = modules
 		.filter(module => !module.excludeFromSourcemap)
 		.map(module => {
-			let sourcemapChain = module.sourcemapChain;
-
 			let source: Source;
-			const originalSourcemap = module.originalSourcemap as ExistingRawSourceMap;
+			const originalSourcemap = module.originalSourcemap;
 			if (!originalSourcemap) {
 				source = new Source(module.id, module.originalCode);
 			} else {
 				const sources = originalSourcemap.sources;
 				const sourcesContent = originalSourcemap.sourcesContent || [];
 
-				if (sources == null || (sources.length <= 1 && sources[0] == null)) {
-					source = new Source(module.id, sourcesContent[0]);
-					sourcemapChain = [originalSourcemap].concat(sourcemapChain);
-				} else {
-					// TODO indiscriminately treating IDs and sources as normal paths is probably bad.
-					const directory = dirname(module.id) || '.';
-					const sourceRoot = originalSourcemap.sourceRoot || '.';
+				// TODO indiscriminately treating IDs and sources as normal paths is probably bad.
+				const directory = dirname(module.id) || '.';
+				const sourceRoot = originalSourcemap.sourceRoot || '.';
 
-					const baseSources = sources.map(
-						(source, i) => new Source(resolve(directory, sourceRoot, source), sourcesContent[i])
-					);
+				const baseSources = sources.map(
+					(source, i) => new Source(resolve(directory, sourceRoot, source), sourcesContent[i])
+				);
 
-					source = new Link(originalSourcemap as any, baseSources) as any;
-				}
+				source = new Link(originalSourcemap as any, baseSources) as any;
 			}
 
-			source = sourcemapChain.reduce(linkMap as any, source);
+			source = module.sourcemapChain.reduce(linkMap as any, source);
 
 			return source;
 		});

From 5aa3542810006d4a5ac5555320c2b43fb2afa904 Mon Sep 17 00:00:00 2001
From: Justin Ridgewell <jridgewell@google.com>
Date: Thu, 4 Jul 2019 01:45:00 -0400
Subject: [PATCH 05/17] Specify Link|Source type

---
 src/Module.ts                   |  1 -
 src/utils/collapseSourcemaps.ts | 15 +++++++++------
 2 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/src/Module.ts b/src/Module.ts
index 1d272f7162c..bf30ec88ff2 100644
--- a/src/Module.ts
+++ b/src/Module.ts
@@ -204,7 +204,6 @@ export default class Module {
 	reexports: { [name: string]: ReexportDescription } = Object.create(null);
 	resolvedIds!: ResolvedIdMap;
 	scope!: ModuleScope;
-	// TODO(jridgewell)
 	sourcemapChain!: DecodedSourceMapOrMissing[];
 	sources: string[] = [];
 	transformAssets?: Asset[];
diff --git a/src/utils/collapseSourcemaps.ts b/src/utils/collapseSourcemaps.ts
index d84befd5e24..fe8f665da98 100644
--- a/src/utils/collapseSourcemaps.ts
+++ b/src/utils/collapseSourcemaps.ts
@@ -35,9 +35,12 @@ interface SourceMapSegmentObject {
 class Link {
 	mappings: SourceMapSegmentVector[][];
 	names: string[];
-	sources: Source[];
+	sources: (Source | Link)[];
 
-	constructor(map: { mappings: SourceMapSegmentVector[][]; names: string[] }, sources: Source[]) {
+	constructor(
+		map: { mappings: SourceMapSegmentVector[][]; names: string[] },
+		sources: (Source | Link)[]
+	) {
 		this.sources = sources;
 		this.names = map.names;
 		this.mappings = map.mappings;
@@ -108,7 +111,7 @@ class Link {
 		return { sources, sourcesContent, names, mappings };
 	}
 
-	traceSegment(line: number, column: number, name: string) {
+	traceSegment(line: number, column: number, name: string): SourceMapSegmentObject | null {
 		const segments = this.mappings[line];
 		if (!segments) return null;
 
@@ -149,7 +152,7 @@ export default function collapseSourcemaps(
 	bundleSourcemapChain: DecodedSourceMapOrMissing[],
 	excludeContent: boolean
 ) {
-	function linkMap(source: Source, map: any) {
+	function linkMap(source: Source | Link, map: any) {
 		// TODO(jridgewell): missing
 		if (map.missing) {
 			bundle.graph.warn({
@@ -173,7 +176,7 @@ export default function collapseSourcemaps(
 	const moduleSources = modules
 		.filter(module => !module.excludeFromSourcemap)
 		.map(module => {
-			let source: Source;
+			let source: Source | Link;
 			const originalSourcemap = module.originalSourcemap;
 			if (!originalSourcemap) {
 				source = new Source(module.id, module.originalCode);
@@ -189,7 +192,7 @@ export default function collapseSourcemaps(
 					(source, i) => new Source(resolve(directory, sourceRoot, source), sourcesContent[i])
 				);
 
-				source = new Link(originalSourcemap as any, baseSources) as any;
+				source = new Link(originalSourcemap as any, baseSources);
 			}
 
 			source = module.sourcemapChain.reduce(linkMap as any, source);

From 93ee458890b5eb7e58850b6061102bec9b903a71 Mon Sep 17 00:00:00 2001
From: Justin Ridgewell <jridgewell@google.com>
Date: Thu, 4 Jul 2019 01:48:53 -0400
Subject: [PATCH 06/17] Handle missing map in collapseSourcemaps

---
 src/utils/collapseSourcemaps.ts | 43 ++++++++++++++++-----------------
 1 file changed, 21 insertions(+), 22 deletions(-)

diff --git a/src/utils/collapseSourcemaps.ts b/src/utils/collapseSourcemaps.ts
index fe8f665da98..48d8fb3e479 100644
--- a/src/utils/collapseSourcemaps.ts
+++ b/src/utils/collapseSourcemaps.ts
@@ -37,13 +37,10 @@ class Link {
 	names: string[];
 	sources: (Source | Link)[];
 
-	constructor(
-		map: { mappings: SourceMapSegmentVector[][]; names: string[] },
-		sources: (Source | Link)[]
-	) {
+	constructor(map: { mappings: number[][][]; names: string[] }, sources: (Source | Link)[]) {
 		this.sources = sources;
 		this.names = map.names;
-		this.mappings = map.mappings;
+		this.mappings = map.mappings as SourceMapSegmentVector[][];
 	}
 
 	traceMappings() {
@@ -152,25 +149,27 @@ export default function collapseSourcemaps(
 	bundleSourcemapChain: DecodedSourceMapOrMissing[],
 	excludeContent: boolean
 ) {
-	function linkMap(source: Source | Link, map: any) {
-		// TODO(jridgewell): missing
-		if (map.missing) {
-			bundle.graph.warn({
-				code: 'SOURCEMAP_BROKEN',
-				message: `Sourcemap is likely to be incorrect: a plugin${
-					map.plugin ? ` ('${map.plugin}')` : ``
-				} was used to transform files, but didn't generate a sourcemap for the transformation. Consult the plugin documentation for help`,
-				plugin: map.plugin,
-				url: `https://rollupjs.org/guide/en/#warning-sourcemap-is-likely-to-be-incorrect`
-			});
-
-			map = {
-				mappings: '',
-				names: []
-			};
+	function linkMap(source: Source | Link, map: DecodedSourceMapOrMissing) {
+		if (map.mappings) {
+			return new Link(map, [source]);
 		}
 
-		return new Link(map, [source]);
+		bundle.graph.warn({
+			code: 'SOURCEMAP_BROKEN',
+			message: `Sourcemap is likely to be incorrect: a plugin${
+				map.plugin ? ` ('${map.plugin}')` : ``
+			} was used to transform files, but didn't generate a sourcemap for the transformation. Consult the plugin documentation for help`,
+			plugin: map.plugin,
+			url: `https://rollupjs.org/guide/en/#warning-sourcemap-is-likely-to-be-incorrect`
+		});
+
+		return new Link(
+			{
+				mappings: [],
+				names: []
+			},
+			[source]
+		);
 	}
 
 	const moduleSources = modules

From 2eeed53f661f5521e01a560405c391a6725dcfa9 Mon Sep 17 00:00:00 2001
From: Justin Ridgewell <jridgewell@google.com>
Date: Thu, 4 Jul 2019 01:50:17 -0400
Subject: [PATCH 07/17] Remove remaining any casts

---
 src/utils/collapseSourcemaps.ts | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/src/utils/collapseSourcemaps.ts b/src/utils/collapseSourcemaps.ts
index 48d8fb3e479..097fd3fdffd 100644
--- a/src/utils/collapseSourcemaps.ts
+++ b/src/utils/collapseSourcemaps.ts
@@ -140,7 +140,6 @@ class Link {
 	}
 }
 
-// TODO TypeScript: Fix <any> typecasts
 export default function collapseSourcemaps(
 	bundle: Chunk,
 	file: string,
@@ -191,17 +190,17 @@ export default function collapseSourcemaps(
 					(source, i) => new Source(resolve(directory, sourceRoot, source), sourcesContent[i])
 				);
 
-				source = new Link(originalSourcemap as any, baseSources);
+				source = new Link(originalSourcemap, baseSources);
 			}
 
-			source = module.sourcemapChain.reduce(linkMap as any, source);
+			source = module.sourcemapChain.reduce(linkMap, source);
 
 			return source;
 		});
 
-	let source = new Link(map as any, moduleSources);
+	let source = new Link(map, moduleSources);
 
-	source = bundleSourcemapChain.reduce(linkMap as any, source);
+	source = bundleSourcemapChain.reduce(linkMap, source);
 
 	let { sources, sourcesContent, names, mappings } = source.traceMappings();
 

From 9027baf87fb0040c24501d974c7787c7013ffea9 Mon Sep 17 00:00:00 2001
From: Justin Ridgewell <jridgewell@google.com>
Date: Thu, 4 Jul 2019 01:54:20 -0400
Subject: [PATCH 08/17] Handle single item SourceMapSegmentVector

---
 src/utils/collapseSourcemaps.ts | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/src/utils/collapseSourcemaps.ts b/src/utils/collapseSourcemaps.ts
index 097fd3fdffd..8709edb7cf9 100644
--- a/src/utils/collapseSourcemaps.ts
+++ b/src/utils/collapseSourcemaps.ts
@@ -22,8 +22,9 @@ class Source {
 }
 
 type SourceMapSegmentVector =
-	| [number, number, number, number, number]
-	| [number, number, number, number];
+	| [number]
+	| [number, number, number, number]
+	| [number, number, number, number, number];
 
 interface SourceMapSegmentObject {
 	column: number;
@@ -54,6 +55,7 @@ class Link {
 			const tracedLine: SourceMapSegmentVector[] = [];
 
 			for (const segment of line) {
+				if (segment.length == 1) continue;
 				const source = this.sources[segment[1]];
 				if (!source) continue;
 
@@ -120,6 +122,7 @@ class Link {
 			const m = (i + j) >> 1;
 			const segment = segments[m];
 			if (segment[0] === column) {
+				if (segment.length == 1) return null;
 				const source = this.sources[segment[1]];
 				if (!source) return null;
 

From 417e76f2d1c467f69ca959c9789837291622e8b8 Mon Sep 17 00:00:00 2001
From: Justin Ridgewell <jridgewell@google.com>
Date: Thu, 4 Jul 2019 02:06:04 -0400
Subject: [PATCH 09/17] Fix tests

---
 .../transform-without-sourcemap/_config.js           | 12 ++++++++++++
 test/sourcemaps/samples/loaders/_config.js           |  4 +---
 .../_config.js                                       | 12 ++++++++++++
 3 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/test/sourcemaps/samples/deprecated/transform-without-sourcemap/_config.js b/test/sourcemaps/samples/deprecated/transform-without-sourcemap/_config.js
index 0e08b7d75fc..921c7fcb3f0 100644
--- a/test/sourcemaps/samples/deprecated/transform-without-sourcemap/_config.js
+++ b/test/sourcemaps/samples/deprecated/transform-without-sourcemap/_config.js
@@ -32,6 +32,18 @@ module.exports = {
 			plugin: 'fake plugin 1',
 			message: `Sourcemap is likely to be incorrect: a plugin ('fake plugin 1') was used to transform files, but didn't generate a sourcemap for the transformation. Consult the plugin documentation for help`,
 			url: `https://rollupjs.org/guide/en/#warning-sourcemap-is-likely-to-be-incorrect`
+		},
+		{
+			code: `SOURCEMAP_BROKEN`,
+			plugin: 'fake plugin 2',
+			message: `Sourcemap is likely to be incorrect: a plugin ('fake plugin 2') was used to transform files, but didn't generate a sourcemap for the transformation. Consult the plugin documentation for help`,
+			url: `https://rollupjs.org/guide/en/#warning-sourcemap-is-likely-to-be-incorrect`
+		},
+		{
+			code: `SOURCEMAP_BROKEN`,
+			plugin: 'fake plugin 2',
+			message: `Sourcemap is likely to be incorrect: a plugin ('fake plugin 2') was used to transform files, but didn't generate a sourcemap for the transformation. Consult the plugin documentation for help`,
+			url: `https://rollupjs.org/guide/en/#warning-sourcemap-is-likely-to-be-incorrect`
 		}
 	]
 };
diff --git a/test/sourcemaps/samples/loaders/_config.js b/test/sourcemaps/samples/loaders/_config.js
index 842e4f55a45..c8169ae1d10 100644
--- a/test/sourcemaps/samples/loaders/_config.js
+++ b/test/sourcemaps/samples/loaders/_config.js
@@ -24,9 +24,7 @@ module.exports = {
 						source: id
 					});
 
-					if (/main.js$/.test(id)) {
-						delete out.map.sources;
-					} else {
+					if (!/main.js$/.test(id)) {
 						const slash = out.map.sources[0].lastIndexOf('/') + 1;
 						out.map.sources = out.map.sources.map(source => '../' + source.slice(slash));
 						out.map.sourceRoot = 'fake';
diff --git a/test/sourcemaps/samples/transform-without-sourcemap-render-chunk/_config.js b/test/sourcemaps/samples/transform-without-sourcemap-render-chunk/_config.js
index 703d4c85cad..4588f70afe9 100644
--- a/test/sourcemaps/samples/transform-without-sourcemap-render-chunk/_config.js
+++ b/test/sourcemaps/samples/transform-without-sourcemap-render-chunk/_config.js
@@ -25,6 +25,18 @@ module.exports = {
 			plugin: 'fake plugin 1',
 			message: `Sourcemap is likely to be incorrect: a plugin ('fake plugin 1') was used to transform files, but didn't generate a sourcemap for the transformation. Consult the plugin documentation for help`,
 			url: `https://rollupjs.org/guide/en/#warning-sourcemap-is-likely-to-be-incorrect`
+		},
+		{
+			code: `SOURCEMAP_BROKEN`,
+			plugin: 'fake plugin 2',
+			message: `Sourcemap is likely to be incorrect: a plugin ('fake plugin 2') was used to transform files, but didn't generate a sourcemap for the transformation. Consult the plugin documentation for help`,
+			url: `https://rollupjs.org/guide/en/#warning-sourcemap-is-likely-to-be-incorrect`
+		},
+		{
+			code: `SOURCEMAP_BROKEN`,
+			plugin: 'fake plugin 2',
+			message: `Sourcemap is likely to be incorrect: a plugin ('fake plugin 2') was used to transform files, but didn't generate a sourcemap for the transformation. Consult the plugin documentation for help`,
+			url: `https://rollupjs.org/guide/en/#warning-sourcemap-is-likely-to-be-incorrect`
 		}
 	]
 };

From 38f52add9edc8fcf15cfc45166da6e92be82f7b1 Mon Sep 17 00:00:00 2001
From: Justin Ridgewell <jridgewell@google.com>
Date: Thu, 4 Jul 2019 02:11:58 -0400
Subject: [PATCH 10/17] Fix lint issues

---
 src/utils/collapseSourcemaps.ts | 2 +-
 src/utils/renderChunk.ts        | 1 -
 src/utils/transform.ts          | 2 --
 3 files changed, 1 insertion(+), 4 deletions(-)

diff --git a/src/utils/collapseSourcemaps.ts b/src/utils/collapseSourcemaps.ts
index 8709edb7cf9..dabbe02281a 100644
--- a/src/utils/collapseSourcemaps.ts
+++ b/src/utils/collapseSourcemaps.ts
@@ -1,7 +1,7 @@
 import { DecodedSourceMap, SourceMap } from 'magic-string';
 import Chunk from '../Chunk';
 import Module from '../Module';
-import { DecodedSourceMapOrMissing, ExistingRawSourceMap } from '../rollup/types';
+import { DecodedSourceMapOrMissing } from '../rollup/types';
 import { error } from './error';
 import { basename, dirname, relative, resolve } from './path';
 
diff --git a/src/utils/renderChunk.ts b/src/utils/renderChunk.ts
index 3b23060d5a7..c5e372f0a67 100644
--- a/src/utils/renderChunk.ts
+++ b/src/utils/renderChunk.ts
@@ -1,4 +1,3 @@
-import { decode } from 'sourcemap-codec';
 import Chunk from '../Chunk';
 import Graph from '../Graph';
 import {
diff --git a/src/utils/transform.ts b/src/utils/transform.ts
index a13000d12b1..a96dd3df13d 100644
--- a/src/utils/transform.ts
+++ b/src/utils/transform.ts
@@ -1,4 +1,3 @@
-import { decode } from 'sourcemap-codec';
 import Graph from '../Graph';
 import Module from '../Module';
 import {
@@ -6,7 +5,6 @@ import {
 	DecodedSourceMapOrMissing,
 	EmitAsset,
 	EmittedChunk,
-	ExistingRawSourceMap,
 	Plugin,
 	PluginCache,
 	PluginContext,

From 550dbeecf6bf5a6b24941e2c5ff607b7960561aa Mon Sep 17 00:00:00 2001
From: Justin Ridgewell <jridgewell@google.com>
Date: Thu, 4 Jul 2019 02:25:36 -0400
Subject: [PATCH 11/17] Handle null sourcemaps meaning no change in code

---
 src/rollup/types.d.ts                                | 12 +++++++-----
 src/utils/renderChunk.ts                             | 12 ++++++++----
 src/utils/transform.ts                               |  9 ++++++---
 .../transform-without-sourcemap/_config.js           | 12 ------------
 .../_config.js                                       | 12 ------------
 5 files changed, 21 insertions(+), 36 deletions(-)

diff --git a/src/rollup/types.d.ts b/src/rollup/types.d.ts
index da007f5dd86..83e5dcdc7f0 100644
--- a/src/rollup/types.d.ts
+++ b/src/rollup/types.d.ts
@@ -77,10 +77,12 @@ export interface SourceMap {
 	toUrl(): string;
 }
 
+export type SourceMapInput = ExistingRawSourceMap | string | null;
+
 export interface SourceDescription {
 	ast?: ESTree.Program;
 	code: string;
-	map?: string | ExistingRawSourceMap;
+	map?: SourceMapInput;
 	moduleSideEffects?: boolean | null;
 }
 
@@ -224,8 +226,8 @@ export type TransformChunkHook = (
 	code: string,
 	options: OutputOptions
 ) =>
-	| Promise<{ code: string; map?: ExistingRawSourceMap | string } | null | undefined>
-	| { code: string; map?: ExistingRawSourceMap | string }
+	| Promise<{ code: string; map?: SourceMapInput } | null | undefined>
+	| { code: string; map?: SourceMapInput }
 	| null
 	| undefined;
 
@@ -235,8 +237,8 @@ export type RenderChunkHook = (
 	chunk: RenderedChunk,
 	options: OutputOptions
 ) =>
-	| Promise<{ code: string; map?: ExistingRawSourceMap | string } | null>
-	| { code: string; map?: ExistingRawSourceMap | string }
+	| Promise<{ code: string; map?: SourceMapInput } | null>
+	| { code: string; map?: SourceMapInput }
 	| string
 	| null;
 
diff --git a/src/utils/renderChunk.ts b/src/utils/renderChunk.ts
index c5e372f0a67..8c2cb96189c 100644
--- a/src/utils/renderChunk.ts
+++ b/src/utils/renderChunk.ts
@@ -5,7 +5,8 @@ import {
 	ExistingRawSourceMap,
 	OutputOptions,
 	Plugin,
-	RenderedChunk
+	RenderedChunk,
+	SourceMapInput
 } from '../rollup/types';
 import { decodedSourcemap } from './decodedSourcemap';
 import { error } from './error';
@@ -27,7 +28,7 @@ export default function renderChunk({
 }): Promise<string> {
 	const renderChunkReducer = (
 		code: string,
-		result: { code: string; map?: ExistingRawSourceMap | string },
+		result: { code: string; map?: SourceMapInput },
 		plugin: Plugin
 	): string => {
 		if (result == null) return code;
@@ -38,8 +39,11 @@ export default function renderChunk({
 				map: undefined
 			};
 
-		const map = decodedSourcemap(result.map);
-		sourcemapChain.push(map || { missing: true, plugin: plugin.name });
+		// null means code was not moved by the plugin.
+		if (result.map !== null) {
+			const map = decodedSourcemap(result.map);
+			sourcemapChain.push(map || { missing: true, plugin: plugin.name });
+		}
 
 		return result.code;
 	};
diff --git a/src/utils/transform.ts b/src/utils/transform.ts
index a96dd3df13d..2316b0ec37c 100644
--- a/src/utils/transform.ts
+++ b/src/utils/transform.ts
@@ -28,7 +28,7 @@ export default function transform(
 	const id = module.id;
 	const sourcemapChain: DecodedSourceMapOrMissing[] = [];
 
-	const originalSourcemap = decodedSourcemap(source.map);
+	const originalSourcemap = source.map === null ? null : decodedSourcemap(source.map);
 	const baseEmitAsset = graph.pluginDriver.emitAsset;
 	const originalCode = source.code;
 	let ast = source.ast;
@@ -92,8 +92,11 @@ export default function transform(
 			return code;
 		}
 
-		const map = decodedSourcemap(result.map);
-		sourcemapChain.push(map || { missing: true, plugin: plugin.name });
+		// null means code was not moved by the plugin.
+		if (result.map !== null) {
+			const map = decodedSourcemap(result.map);
+			sourcemapChain.push(map || { missing: true, plugin: plugin.name });
+		}
 
 		ast = result.ast;
 
diff --git a/test/sourcemaps/samples/deprecated/transform-without-sourcemap/_config.js b/test/sourcemaps/samples/deprecated/transform-without-sourcemap/_config.js
index 921c7fcb3f0..0e08b7d75fc 100644
--- a/test/sourcemaps/samples/deprecated/transform-without-sourcemap/_config.js
+++ b/test/sourcemaps/samples/deprecated/transform-without-sourcemap/_config.js
@@ -32,18 +32,6 @@ module.exports = {
 			plugin: 'fake plugin 1',
 			message: `Sourcemap is likely to be incorrect: a plugin ('fake plugin 1') was used to transform files, but didn't generate a sourcemap for the transformation. Consult the plugin documentation for help`,
 			url: `https://rollupjs.org/guide/en/#warning-sourcemap-is-likely-to-be-incorrect`
-		},
-		{
-			code: `SOURCEMAP_BROKEN`,
-			plugin: 'fake plugin 2',
-			message: `Sourcemap is likely to be incorrect: a plugin ('fake plugin 2') was used to transform files, but didn't generate a sourcemap for the transformation. Consult the plugin documentation for help`,
-			url: `https://rollupjs.org/guide/en/#warning-sourcemap-is-likely-to-be-incorrect`
-		},
-		{
-			code: `SOURCEMAP_BROKEN`,
-			plugin: 'fake plugin 2',
-			message: `Sourcemap is likely to be incorrect: a plugin ('fake plugin 2') was used to transform files, but didn't generate a sourcemap for the transformation. Consult the plugin documentation for help`,
-			url: `https://rollupjs.org/guide/en/#warning-sourcemap-is-likely-to-be-incorrect`
 		}
 	]
 };
diff --git a/test/sourcemaps/samples/transform-without-sourcemap-render-chunk/_config.js b/test/sourcemaps/samples/transform-without-sourcemap-render-chunk/_config.js
index 4588f70afe9..703d4c85cad 100644
--- a/test/sourcemaps/samples/transform-without-sourcemap-render-chunk/_config.js
+++ b/test/sourcemaps/samples/transform-without-sourcemap-render-chunk/_config.js
@@ -25,18 +25,6 @@ module.exports = {
 			plugin: 'fake plugin 1',
 			message: `Sourcemap is likely to be incorrect: a plugin ('fake plugin 1') was used to transform files, but didn't generate a sourcemap for the transformation. Consult the plugin documentation for help`,
 			url: `https://rollupjs.org/guide/en/#warning-sourcemap-is-likely-to-be-incorrect`
-		},
-		{
-			code: `SOURCEMAP_BROKEN`,
-			plugin: 'fake plugin 2',
-			message: `Sourcemap is likely to be incorrect: a plugin ('fake plugin 2') was used to transform files, but didn't generate a sourcemap for the transformation. Consult the plugin documentation for help`,
-			url: `https://rollupjs.org/guide/en/#warning-sourcemap-is-likely-to-be-incorrect`
-		},
-		{
-			code: `SOURCEMAP_BROKEN`,
-			plugin: 'fake plugin 2',
-			message: `Sourcemap is likely to be incorrect: a plugin ('fake plugin 2') was used to transform files, but didn't generate a sourcemap for the transformation. Consult the plugin documentation for help`,
-			url: `https://rollupjs.org/guide/en/#warning-sourcemap-is-likely-to-be-incorrect`
 		}
 	]
 };

From ae28f186b1cf4ace740e8622c4c051fb75b26898 Mon Sep 17 00:00:00 2001
From: Justin Ridgewell <jridgewell@google.com>
Date: Thu, 4 Jul 2019 02:48:04 -0400
Subject: [PATCH 12/17] Handle a no-mappings sourcemap

---
 src/rollup/types.d.ts                          |  2 +-
 src/utils/decodedSourcemap.ts                  | 14 +++++++++++---
 .../_config.js                                 | 18 ++++++++++++++++++
 .../main.js                                    |  1 +
 4 files changed, 31 insertions(+), 4 deletions(-)
 create mode 100644 test/function/samples/handles-empty-string-sourcemap-mappings/_config.js
 create mode 100644 test/function/samples/handles-empty-string-sourcemap-mappings/main.js

diff --git a/src/rollup/types.d.ts b/src/rollup/types.d.ts
index 83e5dcdc7f0..c63653e4b82 100644
--- a/src/rollup/types.d.ts
+++ b/src/rollup/types.d.ts
@@ -77,7 +77,7 @@ export interface SourceMap {
 	toUrl(): string;
 }
 
-export type SourceMapInput = ExistingRawSourceMap | string | null;
+export type SourceMapInput = ExistingRawSourceMap | string | null | { mappings: '' };
 
 export interface SourceDescription {
 	ast?: ESTree.Program;
diff --git a/src/utils/decodedSourcemap.ts b/src/utils/decodedSourcemap.ts
index 3b9316695d8..ecc54f17cab 100644
--- a/src/utils/decodedSourcemap.ts
+++ b/src/utils/decodedSourcemap.ts
@@ -1,7 +1,7 @@
 import { decode } from 'sourcemap-codec';
-import { ExistingDecodedSourceMap, ExistingRawSourceMap } from '../rollup/types';
+import { ExistingDecodedSourceMap, ExistingRawSourceMap, SourceMapInput } from '../rollup/types';
 
-type Input = ExistingRawSourceMap | ExistingDecodedSourceMap | string | undefined;
+type Input = SourceMapInput | ExistingDecodedSourceMap | undefined;
 
 export function decodedSourcemap(map: Input): ExistingDecodedSourceMap | null {
 	if (!map) return null;
@@ -9,6 +9,14 @@ export function decodedSourcemap(map: Input): ExistingDecodedSourceMap | null {
 	if (typeof map === 'string') {
 		map = JSON.parse(map) as ExistingRawSourceMap;
 	}
+	if (map.mappings === '') {
+		return {
+			mappings: [],
+			names: [],
+			sources: [],
+			version: 3
+		};
+	}
 
 	let mappings: number[][][];
 	if (typeof map.mappings === 'string') {
@@ -17,5 +25,5 @@ export function decodedSourcemap(map: Input): ExistingDecodedSourceMap | null {
 		mappings = map.mappings;
 	}
 
-	return { ...map, mappings };
+	return { ...(map as ExistingRawSourceMap | ExistingDecodedSourceMap), mappings };
 }
diff --git a/test/function/samples/handles-empty-string-sourcemap-mappings/_config.js b/test/function/samples/handles-empty-string-sourcemap-mappings/_config.js
new file mode 100644
index 00000000000..764c77a324a
--- /dev/null
+++ b/test/function/samples/handles-empty-string-sourcemap-mappings/_config.js
@@ -0,0 +1,18 @@
+module.exports = {
+	description: 'handles transforms that return sourcemap with empty mappings',
+
+	options: {
+		plugins: [
+			{
+				transform(code) {
+					return {
+						code,
+						map: { mappings: '' }
+					};
+				}
+			}
+		],
+		// ensure source maps are generated
+		output: { sourcemap: true }
+	}
+};
diff --git a/test/function/samples/handles-empty-string-sourcemap-mappings/main.js b/test/function/samples/handles-empty-string-sourcemap-mappings/main.js
new file mode 100644
index 00000000000..7a4e8a723a4
--- /dev/null
+++ b/test/function/samples/handles-empty-string-sourcemap-mappings/main.js
@@ -0,0 +1 @@
+export default 42;

From 4de681a2f449e4a2b5e3dd7ba14f88e4889d5d47 Mon Sep 17 00:00:00 2001
From: Justin Ridgewell <jridgewell@google.com>
Date: Thu, 4 Jul 2019 15:48:35 -0400
Subject: [PATCH 13/17] Remove sourcemap-coded declaration

It has types now
---
 src/utils/renderChunk.ts  | 1 -
 typings/declarations.d.ts | 3 ---
 2 files changed, 4 deletions(-)

diff --git a/src/utils/renderChunk.ts b/src/utils/renderChunk.ts
index 8c2cb96189c..c2d98106c41 100644
--- a/src/utils/renderChunk.ts
+++ b/src/utils/renderChunk.ts
@@ -2,7 +2,6 @@ import Chunk from '../Chunk';
 import Graph from '../Graph';
 import {
 	DecodedSourceMapOrMissing,
-	ExistingRawSourceMap,
 	OutputOptions,
 	Plugin,
 	RenderedChunk,
diff --git a/typings/declarations.d.ts b/typings/declarations.d.ts
index 5a94638f7ee..100ca939fa2 100644
--- a/typings/declarations.d.ts
+++ b/typings/declarations.d.ts
@@ -12,9 +12,6 @@ declare module 'signal-exit';
 declare module 'date-time';
 declare module 'locate-character';
 declare module 'is-reference';
-declare module 'sourcemap-codec' {
-	export function decode(mappings: string): number[][][];
-}
 declare module 'require-relative';
 declare module 'acorn-dynamic-import';
 declare module 'acorn-import-meta';

From aaa055867497cafffb8344c57c482fe609a3eb2f Mon Sep 17 00:00:00 2001
From: Justin Ridgewell <jridgewell@google.com>
Date: Thu, 4 Jul 2019 15:51:45 -0400
Subject: [PATCH 14/17] Undo comment changes

---
 src/utils/renderChunk.ts | 2 +-
 src/utils/transform.ts   | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/utils/renderChunk.ts b/src/utils/renderChunk.ts
index c2d98106c41..d53be7c376b 100644
--- a/src/utils/renderChunk.ts
+++ b/src/utils/renderChunk.ts
@@ -38,7 +38,7 @@ export default function renderChunk({
 				map: undefined
 			};
 
-		// null means code was not moved by the plugin.
+		// strict null check allows 'null' maps to not be pushed to the chain, while 'undefined' gets the missing map warning
 		if (result.map !== null) {
 			const map = decodedSourcemap(result.map);
 			sourcemapChain.push(map || { missing: true, plugin: plugin.name });
diff --git a/src/utils/transform.ts b/src/utils/transform.ts
index 2316b0ec37c..3bf570fbd6d 100644
--- a/src/utils/transform.ts
+++ b/src/utils/transform.ts
@@ -92,7 +92,7 @@ export default function transform(
 			return code;
 		}
 
-		// null means code was not moved by the plugin.
+		// strict null check allows 'null' maps to not be pushed to the chain, while 'undefined' gets the missing map warning
 		if (result.map !== null) {
 			const map = decodedSourcemap(result.map);
 			sourcemapChain.push(map || { missing: true, plugin: plugin.name });

From f936eeb1ac3e5ff753c95082d9ee9996f44cecb8 Mon Sep 17 00:00:00 2001
From: Justin Ridgewell <jridgewell@google.com>
Date: Thu, 4 Jul 2019 16:12:42 -0400
Subject: [PATCH 15/17] Use sourcemap-codec's types

---
 src/utils/collapseSourcemaps.ts | 16 ++++++----------
 1 file changed, 6 insertions(+), 10 deletions(-)

diff --git a/src/utils/collapseSourcemaps.ts b/src/utils/collapseSourcemaps.ts
index dabbe02281a..5face4b5eb1 100644
--- a/src/utils/collapseSourcemaps.ts
+++ b/src/utils/collapseSourcemaps.ts
@@ -1,4 +1,5 @@
 import { DecodedSourceMap, SourceMap } from 'magic-string';
+import { SourceMapLine, SourceMapMappings, SourceMapSegment } from 'sourcemap-codec';
 import Chunk from '../Chunk';
 import Module from '../Module';
 import { DecodedSourceMapOrMissing } from '../rollup/types';
@@ -21,11 +22,6 @@ class Source {
 	}
 }
 
-type SourceMapSegmentVector =
-	| [number]
-	| [number, number, number, number]
-	| [number, number, number, number, number];
-
 interface SourceMapSegmentObject {
 	column: number;
 	line: number;
@@ -34,14 +30,14 @@ interface SourceMapSegmentObject {
 }
 
 class Link {
-	mappings: SourceMapSegmentVector[][];
+	mappings: SourceMapMappings;
 	names: string[];
 	sources: (Source | Link)[];
 
 	constructor(map: { mappings: number[][][]; names: string[] }, sources: (Source | Link)[]) {
 		this.sources = sources;
 		this.names = map.names;
-		this.mappings = map.mappings as SourceMapSegmentVector[][];
+		this.mappings = map.mappings as SourceMapMappings;
 	}
 
 	traceMappings() {
@@ -52,7 +48,7 @@ class Link {
 		const mappings = [];
 
 		for (const line of this.mappings) {
-			const tracedLine: SourceMapSegmentVector[] = [];
+			const tracedLine: SourceMapLine = [];
 
 			for (const segment of line) {
 				if (segment.length == 1) continue;
@@ -83,7 +79,7 @@ class Link {
 						});
 					}
 
-					const tracedSegment: SourceMapSegmentVector = [
+					const tracedSegment: SourceMapSegment = [
 						segment[0],
 						sourceIndex,
 						traced.line,
@@ -97,7 +93,7 @@ class Link {
 							names.push(traced.name);
 						}
 
-						(tracedSegment as SourceMapSegmentVector)[4] = nameIndex;
+						(tracedSegment as SourceMapSegment)[4] = nameIndex;
 					}
 
 					tracedLine.push(tracedSegment);

From 597ad003253c5ce4b0bfb48f84835b6a02b88dbd Mon Sep 17 00:00:00 2001
From: Justin Ridgewell <jridgewell@google.com>
Date: Fri, 5 Jul 2019 15:00:11 -0400
Subject: [PATCH 16/17] Get rid of TODO

---
 src/rollup/types.d.ts | 1 -
 1 file changed, 1 deletion(-)

diff --git a/src/rollup/types.d.ts b/src/rollup/types.d.ts
index c63653e4b82..987c08f3e59 100644
--- a/src/rollup/types.d.ts
+++ b/src/rollup/types.d.ts
@@ -99,7 +99,6 @@ export interface TransformModuleJSON {
 	originalCode: string;
 	originalSourcemap: ExistingDecodedSourceMap | null;
 	resolvedIds?: ResolvedIdMap;
-	// TODO(jridewell)
 	sourcemapChain: DecodedSourceMapOrMissing[];
 	transformDependencies: string[] | null;
 }

From 37ac3e97d72f59cfd5803a3febb745480e2d34e6 Mon Sep 17 00:00:00 2001
From: Justin Ridgewell <justin@ridgewell.name>
Date: Sat, 6 Jul 2019 15:01:37 -0400
Subject: [PATCH 17/17] Use our own SourceMapSegment tuple type

---
 src/rollup/types.d.ts            |  7 ++++++-
 src/utils/collapseSourcemaps.ts  | 26 +++++++++++++++++---------
 src/utils/decodedSourcemap.ts    |  2 +-
 src/utils/getOriginalLocation.ts |  6 +++---
 4 files changed, 27 insertions(+), 14 deletions(-)

diff --git a/src/rollup/types.d.ts b/src/rollup/types.d.ts
index 987c08f3e59..c24a7dded59 100644
--- a/src/rollup/types.d.ts
+++ b/src/rollup/types.d.ts
@@ -38,9 +38,14 @@ export interface RollupLogProps {
 	url?: string;
 }
 
+export type SourceMapSegment =
+	| [number]
+	| [number, number, number, number]
+	| [number, number, number, number, number];
+
 export interface ExistingDecodedSourceMap {
 	file?: string;
-	mappings: number[][][];
+	mappings: SourceMapSegment[][];
 	names: string[];
 	sourceRoot?: string;
 	sources: string[];
diff --git a/src/utils/collapseSourcemaps.ts b/src/utils/collapseSourcemaps.ts
index 5face4b5eb1..a240190b501 100644
--- a/src/utils/collapseSourcemaps.ts
+++ b/src/utils/collapseSourcemaps.ts
@@ -1,8 +1,11 @@
 import { DecodedSourceMap, SourceMap } from 'magic-string';
-import { SourceMapLine, SourceMapMappings, SourceMapSegment } from 'sourcemap-codec';
 import Chunk from '../Chunk';
 import Module from '../Module';
-import { DecodedSourceMapOrMissing } from '../rollup/types';
+import {
+	DecodedSourceMapOrMissing,
+	ExistingDecodedSourceMap,
+	SourceMapSegment
+} from '../rollup/types';
 import { error } from './error';
 import { basename, dirname, relative, resolve } from './path';
 
@@ -30,14 +33,17 @@ interface SourceMapSegmentObject {
 }
 
 class Link {
-	mappings: SourceMapMappings;
+	mappings: SourceMapSegment[][];
 	names: string[];
 	sources: (Source | Link)[];
 
-	constructor(map: { mappings: number[][][]; names: string[] }, sources: (Source | Link)[]) {
+	constructor(
+		map: { mappings: SourceMapSegment[][]; names: string[] },
+		sources: (Source | Link)[]
+	) {
 		this.sources = sources;
 		this.names = map.names;
-		this.mappings = map.mappings as SourceMapMappings;
+		this.mappings = map.mappings;
 	}
 
 	traceMappings() {
@@ -48,7 +54,7 @@ class Link {
 		const mappings = [];
 
 		for (const line of this.mappings) {
-			const tracedLine: SourceMapLine = [];
+			const tracedLine: SourceMapSegment[] = [];
 
 			for (const segment of line) {
 				if (segment.length == 1) continue;
@@ -58,7 +64,7 @@ class Link {
 				const traced = source.traceSegment(
 					segment[2],
 					segment[3],
-					this.names[segment[4] as number]
+					segment.length === 5 ? this.names[segment[4]] : ''
 				);
 
 				if (traced) {
@@ -125,7 +131,7 @@ class Link {
 				return source.traceSegment(
 					segment[2],
 					segment[3],
-					this.names[segment[4] as number] || name
+					segment.length === 5 ? this.names[segment[4]] : name
 				);
 			}
 			if (segment[0] > column) {
@@ -197,7 +203,9 @@ export default function collapseSourcemaps(
 			return source;
 		});
 
-	let source = new Link(map, moduleSources);
+	// DecodedSourceMap (from magic-string) uses a number[] instead of the more
+	// correct SourceMapSegment tuples. Cast it here to gain type safety.
+	let source = new Link(map as ExistingDecodedSourceMap, moduleSources);
 
 	source = bundleSourcemapChain.reduce(linkMap, source);
 
diff --git a/src/utils/decodedSourcemap.ts b/src/utils/decodedSourcemap.ts
index ecc54f17cab..3b4acfcf6a4 100644
--- a/src/utils/decodedSourcemap.ts
+++ b/src/utils/decodedSourcemap.ts
@@ -18,7 +18,7 @@ export function decodedSourcemap(map: Input): ExistingDecodedSourceMap | null {
 		};
 	}
 
-	let mappings: number[][][];
+	let mappings;
 	if (typeof map.mappings === 'string') {
 		mappings = decode(map.mappings);
 	} else {
diff --git a/src/utils/getOriginalLocation.ts b/src/utils/getOriginalLocation.ts
index 0a84fe71184..1da1d7aa7e5 100644
--- a/src/utils/getOriginalLocation.ts
+++ b/src/utils/getOriginalLocation.ts
@@ -11,17 +11,17 @@ export function getOriginalLocation(
 
 	while (filteredSourcemapChain.length > 0) {
 		const sourcemap = filteredSourcemapChain.pop()!;
-		const line: any = sourcemap.mappings[location.line - 1];
+		const line = sourcemap.mappings[location.line - 1];
 		let locationFound = false;
 
 		if (line !== undefined) {
 			for (const segment of line) {
 				if (segment[0] >= location.column) {
-					if (segment.length < 4) break;
+					if (segment.length === 1) break;
 					location = {
 						column: segment[3],
 						line: segment[2] + 1,
-						name: sourcemap.names[segment[4]],
+						name: segment.length === 5 ? sourcemap.names[segment[4]] : undefined,
 						source: sourcemap.sources[segment[1]]
 					};
 					locationFound = true;