fix: plugin warnings not showing warning.loc (#3824)

* fix: plugin warnings not showing warning.loc

Plugin warnings without warning.id but with warning.loc were not emitting loc information
loc information emitting is fundamental for user experience (to locate the source of the error/warning)

* Update batchWarnings.ts

* Add test

Co-authored-by: Lukas Taegert-Atkinson <lukas.taegert-atkinson@tngtech.com>
Co-authored-by: Lukas Taegert-Atkinson <lukastaegert@users.noreply.github.com>

cli/run/batchWarnings.ts

@@ -189,8 +189,9 @@ const deferredHandlers: {
 				for (const warning of items) {
 					if (warning.url && warning.url !== lastUrl) info((lastUrl = warning.url));
 
-					if (warning.id) {
-						let loc = relativeId(warning.id);
+					const id = warning.id || warning.loc?.file;
+					if (id) {
+						let loc = relativeId(id);
 						if (warning.loc) {
 							loc += `: (${warning.loc.line}:${warning.loc.column})`;
 						}

test/cli/samples/warn-plugin-loc/_config.js

@@ -0,0 +1,17 @@
+const { assertIncludes } = require('../../../utils.js');
+
+module.exports = {
+	description: 'correctly adds locations to plugin warnings',
+	command: 'rollup -c',
+	stderr: stderr => {
+		assertIncludes(
+			stderr,
+			'(!) Plugin test: Warning with file and id\n' +
+				'file1: (1:2)\n' +
+				'(!) Plugin test: Warning with file\n' +
+				'file2: (2:3)\n' +
+				'(!) Plugin test: Warning with id\n' +
+				'file-id3: (3:4)\n'
+		);
+	}
+};

test/cli/samples/warn-plugin-loc/main.js

@@ -0,0 +1 @@
+console.log("everyday I'm throwing");

test/cli/samples/warn-plugin-loc/rollup.config.js

@@ -0,0 +1,29 @@
+const path = require('path');
+
+module.exports = {
+	input: 'main.js',
+	output: {
+		format: 'cjs'
+	},
+	plugins: [
+		{
+			name: 'test',
+			buildStart() {
+				this.warn({
+					message: 'Warning with file and id',
+					file: path.join(__dirname, 'file-id1'),
+					loc: { file: path.join(__dirname, 'file1'), line: 1, column: 2 }
+				});
+				this.warn({
+					message: 'Warning with file',
+					loc: { file: path.join(__dirname, 'file2'), line: 2, column: 3 }
+				});
+				this.warn({
+					message: 'Warning with id',
+					id: path.join(__dirname, 'file-id3'),
+					loc: { line: 3, column: 4 }
+				});
+			}
+		}
+	]
+};