build: patch terser to create proper source-maps [do not merge]

WORKSPACE

@@ -20,7 +20,12 @@ http_archive(
     name = "build_bazel_rules_nodejs",
     patch_args = ["-p1"],
     # Patch https://github.com/bazelbuild/rules_nodejs/pull/903
-    patches = ["//tools:rollup_bundle_commonjs_ignoreGlobal.patch"],
+    # Patch "terser" used by the rollup bazel rule to create proper
+    # source-maps: https://github.com/terser-js/terser/pull/342
+    patches = [
+        "//tools:rollup_bundle_commonjs_ignoreGlobal.patch",
+        "//tools:rollup_terser_incorrect_source_maps.patch",
+    ],
     sha256 = "da217044d24abd16667324626a33581f3eaccabf80985b2688d6a08ed2f864be",
     urls = ["https://github.com/bazelbuild/rules_nodejs/releases/download/0.37.1/rules_nodejs-0.37.1.tar.gz"],
 )

tools/rollup_terser_incorrect_source_maps.patch

@@ -0,0 +1,25 @@
+diff --git a/internal/rollup/postinstall-patches.js b/internal/rollup/postinstall-patches.js
+index 3e0720e..0f6f8e7 100644
+--- a/internal/rollup/postinstall-patches.js
++++ b/internal/rollup/postinstall-patches.js
+@@ -43,3 +43,20 @@ console.log(
+     '\n# patch: @buxlabs/amd-to-es6 to generate namespace imports instead of default imports');
+ sed('-i', 'ImportDefaultSpecifier', 'ImportNamespaceSpecifier',
+     'node_modules/@buxlabs/amd-to-es6/src/lib/getImportDeclaration.js');
++
++// Fix terser bug where generated code (e.g. from rollup) is incorrectly mapped to
++// source files. See: https://github.com/terser-js/terser/pull/342
++const terminateSegmentSnippet = `
++  var generatedPos = { line: gen_line + options.dest_line_diff, column: gen_col };
++  if (generatedPos.column !== 0) {
++    generator.addMapping({
++        generated: generatedPos,
++        original: null,
++        source: null,
++        name: null
++    });
++  }
++`
++sed('-i', /if \(info.source === null\) {/, `$& ${terminateSegmentSnippet}`,
++    'node_modules/terser/dist/bundle.js');
++sed('-i', 'process.env.TERSER_NO_BUNDLE', 'true', 'node_modules/terser/bin/uglifyjs');