feat(terser): support source map files (#1195)

Author: gregmagolan

packages/terser/src/terser_minified.bzl

@@ -40,7 +40,7 @@ Can be a .js file, a rule producing .js files as its default output, or a rule p
 
 Note that you can pass multiple files to terser, which it will bundle together.
 If you want to do this, you can pass a filegroup here.""",
-        allow_files = [".js"],
+        allow_files = [".js", ".map", ".mjs"],
         mandatory = True,
     ),
     "config_file": attr.label(
@@ -95,6 +95,9 @@ so that it only affects the current build.
     ),
 }
 
+def _filter_js(files):
+    return [f for f in files if f.is_directory or f.extension == "js" or f.extension == "mjs"]
+
 def _terser(ctx):
     "Generate actions to create terser config run terser"
 
@@ -103,17 +106,19 @@ def _terser(ctx):
     inputs = ctx.files.src[:]
     outputs = []
 
-    directory_srcs = [s for s in ctx.files.src if s.is_directory]
+    sources = _filter_js(inputs)
+    sourcemaps = [f for f in inputs if f.extension == "map"]
+    directory_srcs = [s for s in sources if s.is_directory]
     if len(directory_srcs) > 0:
-        if len(ctx.files.src) > 1:
+        if len(sources) > 1:
             fail("When directories are passed to terser_minified, there should be only one input")
         outputs.append(ctx.actions.declare_directory(ctx.label.name))
     else:
         outputs.append(ctx.actions.declare_file("%s.js" % ctx.label.name))
         if ctx.attr.sourcemap:
             outputs.append(ctx.actions.declare_file("%s.js.map" % ctx.label.name))
 
-    args.add_all([s.path for s in ctx.files.src])
+    args.add_all([s.path for s in sources])
     args.add_all(["--output", outputs[0].path])
 
     debug = ctx.attr.debug or "DEBUG" in ctx.var.keys()
@@ -126,9 +131,12 @@ def _terser(ctx):
         # see https://github.com/terser-js/terser#command-line-usage
         source_map_opts = ["includeSources", "base=" + ctx.bin_dir.path]
 
-        # We support only inline sourcemaps for now.
-        # It's hard to pair up the .js inputs with corresponding .map files
-        source_map_opts.append("content=inline")
+        if len(sourcemaps) == 0:
+            source_map_opts.append("content=inline")
+        elif len(sourcemaps) == 1:
+            source_map_opts.append("content='%s'" % sourcemaps[0].path)
+        else:
+            fail("When sourcemap is True, there should only be one or none input sourcemaps")
 
         # This option doesn't work in the config file, only on the CLI
         args.add_all(["--source-map", ",".join(source_map_opts)])

packages/terser/test/sourcemap/BUILD.bazel

@@ -0,0 +1,26 @@
+load("@npm_bazel_jasmine//:index.from_src.bzl", "jasmine_node_test")
+load("@npm_bazel_terser//:index.from_src.bzl", "terser_minified")
+
+filegroup(
+    name = "src1_and_map",
+    srcs = [
+        "src1.js",
+        "src1.js.map",
+    ],
+)
+
+terser_minified(
+    name = "src1.min",
+    src = ":src1_and_map",
+)
+
+jasmine_node_test(
+    name = "test",
+    srcs = [
+        "terser_spec.js",
+    ],
+    data = ["@npm//source-map"],
+    deps = [
+        ":src1.min",
+    ],
+)

packages/terser/test/sourcemap/README.md

@@ -0,0 +1 @@
+The src1.js{,.map} files were generated from running `tsc --lib es2015,dom --sourcemap --noImplicitUseStrict src1.ts`.

packages/terser/test/sourcemap/src1.js

@@ -0,0 +1,7 @@
+// clang-format off
+/*a comment*/ export class MyClass {
+  constructor(s: string) {
+    console.log(s);
+  }
+  field: string|undefined;
+}

packages/terser/test/sourcemap/src1.js.map

@@ -0,0 +1,20 @@
+const fs = require('fs');
+const sm = require('source-map');
+const DIR = 'build_bazel_rules_nodejs/packages/terser/test/sourcemap';
+
+describe('terser sourcemap handling', () => {
+  it('should produce a sourcemap output', async () => {
+    const file = require.resolve(DIR + '/src1.min.js.map');
+    const rawSourceMap = JSON.parse(fs.readFileSync(file, 'utf-8'));
+    await sm.SourceMapConsumer.with(rawSourceMap, null, consumer => {
+      const pos = consumer.originalPositionFor(
+          // position of MyClass in terser_minified output src1.min.js
+          // depends on DEBUG flag
+          !process.env['DEBUG'] ? {line: 1, column: 18} : {line: 3, column: 5});
+      expect(pos.source).toBe('src1.ts');
+      expect(pos.line).toBe(2);
+      expect(pos.column).toBe(14);
+      expect(pos.name).toBe('MyClass');
+    });
+  });
+});