fix: set sourcemap root to the workspace relative root_dir

examples/filegroup/BUILD.bazel

@@ -5,6 +5,7 @@ filegroup(
     srcs = [
         "a.ts",
         "b.ts",
+        "sub/c.ts",
     ],
 )
 

examples/filegroup/check_outputs.sh

@@ -5,10 +5,17 @@ cd "$TEST_SRCDIR/$TEST_WORKSPACE/$(dirname $TEST_TARGET)"
 
 grep "export var a" filegroup/a.js
 grep "sourceMappingURL=a.js.map" filegroup/a.js
-grep --fixed-strings '"sourceRoot":"examples/filegroup"' filegroup/a.js.map
+grep --fixed-strings '"sourceRoot":""' filegroup/a.js.map
 grep --fixed-strings '"sources":["a.ts"]' filegroup/a.js.map
 
 grep "export var b" filegroup/b.js
 grep "sourceMappingURL=b.js.map" filegroup/b.js
-grep --fixed-strings '"sourceRoot":"examples/filegroup"' filegroup/b.js.map
-grep --fixed-strings '"sources":["b.ts"]' filegroup/b.js.map
+grep --fixed-strings '"sourceRoot":""' filegroup/b.js.map
+grep --fixed-strings '"sources":["b.ts"]' filegroup/b.js.map
+
+grep "export var c" filegroup/sub/c.js
+grep "sourceMappingURL=c.js.map" filegroup/sub/c.js
+grep --fixed-strings '"sourceRoot":""' filegroup/sub/c.js.map
+grep --fixed-strings '"sources":["c.ts"]' filegroup/sub/c.js.map
+
+echo "SUCCESS"

examples/filegroup/sub/c.ts

@@ -0,0 +1 @@
+export const c: string = "c";

examples/package.json

@@ -1,3 +1,6 @@
 {
-  "private": true
+  "private": true,
+  "dependencies": {
+    "source-map-support": "^0.5.21"
+  }
 }

examples/root_dir/BUILD.bazel

@@ -1,28 +1,26 @@
+load("@aspect_bazel_lib//lib:write_source_files.bzl", "write_source_files")
 load("@aspect_rules_swc//swc:defs.bzl", "swc")
-load("@aspect_bazel_lib//lib:testing.bzl", "assert_outputs")
 
 swc(
     name = "compile",
     srcs = [
         "src/a.ts",
         "src/b.ts",
+        "src/sub/c.ts",
     ],
     out_dir = "out",
     root_dir = "src",
     source_maps = True,
 )
 
-# Since the srcs were in a filegroup, the swc macro cannot pre-declare the outputs.
-# So there is no label ":a.js" that we can reference from the build file.
-# However, a.js is still produced as one of the default outputs of the compile rule.
-# We can verify this in an action that depends on the ":compile" rule and reads the files.
-assert_outputs(
-    name = "check_outputs",
-    actual = "compile",
-    expected = [
-        "examples/root_dir/out/a.js",
-        "examples/root_dir/out/a.js.map",
-        "examples/root_dir/out/b.js",
-        "examples/root_dir/out/b.js.map",
-    ],
-)
+write_source_files(
+    name = "test",
+    files = {
+        "expected/a.js": ":out/a.js",
+        "expected/a.js.map": ":out/a.js.map",
+        "expected/b.js": ":out/b.js",
+        "expected/b.js.map": ":out/b.js.map",
+        "expected/sub/c.js": ":out/sub/c.js",
+        "expected/sub/c.js.map": ":out/sub/c.js.map",
+    },
+)

examples/root_dir/src/sub/c.ts

@@ -0,0 +1 @@
+export const c: string = "c";

examples/source_map_support/BUILD.bazel

@@ -0,0 +1,11 @@
+load("@aspect_bazel_lib//lib:copy_to_bin.bzl", "copy_to_bin")
+
+exports_files([
+    "defs.bzl",
+])
+
+copy_to_bin(
+    name = "stack-trace-support",
+    srcs = ["stack-trace-support.js"],
+    visibility = ["//visibility:public"],
+)

examples/source_map_support/defs.bzl

@@ -0,0 +1,28 @@
+"""
+Macro wrappers around rules_js's `js_binary` and `js_test` that improve the DX of stack traces by automatically
+registering source-map-support and removing the runfiles directory prefix.
+
+Use them wherever you would use rules_js's `js_binary` and `js_test`.
+"""
+
+load("@aspect_rules_js//js:defs.bzl", _js_binary = "js_binary", _js_test = "js_test")
+
+def js_binary(data = [], node_options = [], **kwargs):
+    _js_binary(
+        data = [
+            "//examples:node_modules/source-map-support",
+            "//examples/source_map_support:stack-trace-support",
+        ] + data,
+        node_options = ["--require", "$$RUNFILES/aspect_rules_swc/examples/source_map_support/stack-trace-support"] + node_options,
+        **kwargs
+    )
+
+def js_test(data = [], node_options = [], **kwargs):
+    _js_test(
+        data = [
+            "//examples:node_modules/source-map-support",
+            "//examples/source_map_support:stack-trace-support",
+        ] + data,
+        node_options = ["--require", "$$RUNFILES/aspect_rules_swc/examples/source_map_support/stack-trace-support"] + node_options,
+        **kwargs
+    )

examples/source_map_support/stack-trace-support.js

@@ -0,0 +1,42 @@
+// See defs.bzl for where this is used and what it does.
+
+require('source-map-support/register')
+
+let basePath = process.env.RUNFILES
+  ? `${process.env.RUNFILES}/${process.env.JS_BINARY__WORKSPACE}`
+  : process.cwd()
+
+if (!basePath.endsWith('/')) {
+  basePath = basePath + '/'
+}
+
+/*
+Before:
+    Error: test
+        at foo (/private/var/tmp/_bazel_john/67beefda950d56283b98d96980e6e332/execroot/figma/bazel-out/darwin_arm64-fastbuild/bin/bazel/js/test/stack_trace_support.sh.runfiles/figma/bazel/js/test/b.js:2:11)
+        at Object.<anonymous> (/private/var/tmp/_bazel_john/67beefda950d56283b98d96980e6e332/execroot/figma/bazel-out/darwin_arm64-fastbuild/bin/bazel/js/test/stack_trace_support.sh.runfiles/figma/bazel/js/test/a.js:4:1)
+        ...
+
+After:
+    Error: test
+        at foo (bazel/js/test/b.ts:2:9)
+        at Object.<anonymous> (bazel/js/test/a.ts:5:1)
+        ...
+*/
+
+const basePathRegex = new RegExp(
+  `(at | \\()${basePath
+    .replace(/\\/g, '/')
+    // Escape regex meta-characters.
+    .replace(/[|\\{}()[\]^$+*?.]/g, '\\$&')
+    .replace(/-/g, '\\x2d')}`,
+  'g',
+)
+
+const prepareStackTrace = Error.prepareStackTrace
+Error.prepareStackTrace = function (error, stack) {
+  return prepareStackTrace(error, stack)
+    .split('\n')
+    .map((line) => line.replace(basePathRegex, '$1'))
+    .join('\n')
+}

examples/source_map_support/test/BUILD.bazel

@@ -0,0 +1,24 @@
+load("@aspect_rules_swc//swc:defs.bzl", "swc")
+load("//examples/source_map_support:defs.bzl", "js_test")
+
+swc(
+    name = "compile",
+    srcs = [
+        "a.ts",
+        "b.ts",
+    ],
+    source_maps = True,
+)
+
+js_test(
+    name = "stack_trace_support_test",
+    data = [":compile"],
+    entry_point = ":a.js",
+)
+
+js_test(
+    name = "stack_trace_support_with_chdir_test",
+    chdir = "examples",
+    data = [":compile"],
+    entry_point = ":a.js",
+)

examples/source_map_support/test/a.ts

@@ -0,0 +1,17 @@
+try {
+  require('./b')()
+} catch (e) {
+  const assert = require('assert')
+  const frames = e.stack
+    .split('\n')
+    .slice(1)
+    .map((s) => s.trim())
+  assert.deepEqual(
+    frames.filter((f) => f.includes('source_map_support/test/a')),
+    [`at Object.<anonymous> (examples/source_map_support/test/a.ts:2:11)`],
+  )
+  assert.deepEqual(
+    frames.filter((f) => f.includes('source_map_support/test/b')),
+    [`at foo (examples/source_map_support/test/b.ts:2:9)`],
+  )
+}

examples/source_map_support/test/b.ts

@@ -0,0 +1,3 @@
+module.exports = function foo() {
+  throw new Error('test')
+}

swc/private/swc.bzl

@@ -255,7 +255,7 @@ def _impl(ctx):
         for src in ctx.files.srcs:
             src_args = ctx.actions.args()
             src_args.add("--source-file-name", src.basename)
-            src_args.add("--source-root", src.dirname if ctx.attr.source_root == "" else ctx.attr.source_root)
+            src_args.add("--source-root", "" if ctx.attr.source_root == "" else ctx.attr.source_root)
 
             src_path = _relative_to_package(src.path, ctx)