bzltestutil: move os.Chdir call into new package

go/private/rules/test.bzl

@@ -132,7 +132,7 @@ def _go_test_impl(ctx):
     # We add "+initfirst/" to the package path so the package is initialized
     # before user code. See comment above the init function
     # in bzltestutil/init.go.
-    test_gc_linkopts.extend(["-X", "+initfirst/github.com/bazelbuild/rules_go/go/tools/bzltestutil.RunDir=" + run_dir])
+    test_gc_linkopts.extend(["-X", "+initfirst/github.com/bazelbuild/rules_go/go/tools/bzltestutil/chdir.RunDir=" + run_dir])
 
     # Now compile the test binary itself
     test_library = GoLibrary(

go/tools/bzltestutil/BUILD.bazel

@@ -3,17 +3,15 @@ load("//go:def.bzl", "go_test", "go_tool_library")
 go_tool_library(
     name = "bzltestutil",
     srcs = [
-        "init.go",
         "lcov.go",
         "test2json.go",
         "wrap.go",
         "xml.go",
     ],
-    # We add "+initfirst/" to the package path so this package is initialized
-    # before user code. See comment above the init function in init.go.
     importmap = "+initfirst/github.com/bazelbuild/rules_go/go/tools/bzltestutil",
     importpath = "github.com/bazelbuild/rules_go/go/tools/bzltestutil",
     visibility = ["//visibility:public"],
+    deps = ["//go/tools/bzltestutil/chdir"],
 )
 
 go_test(
@@ -34,7 +32,7 @@ go_test(
 filegroup(
     name = "all_files",
     testonly = True,
-    srcs = glob(
+    srcs = ["//go/tools/bzltestutil/chdir:all_files"] + glob(
         ["**"],
         exclude = ["testdata/*"],
     ),

go/tools/bzltestutil/chdir/BUILD.bazel

@@ -0,0 +1,21 @@
+load("//go:def.bzl", "go_tool_library")
+
+go_tool_library(
+    name = "chdir",
+    srcs = ["init.go"],
+    # We add "+initfirst/" to the package path so this package is initialized
+    # before user code. See comment above the init function in init.go.
+    importmap = "+initfirst/github.com/bazelbuild/rules_go/go/tools/bzltestutil/chdir",
+    importpath = "github.com/bazelbuild/rules_go/go/tools/bzltestutil/chdir",
+    visibility = ["//go/tools/bzltestutil:__pkg__"],
+)
+
+filegroup(
+    name = "all_files",
+    testonly = True,
+    srcs = glob(
+        ["**"],
+        exclude = ["testdata/*"],
+    ),
+    visibility = ["//visibility:public"],
+)

go/tools/bzltestutil/chdir/init.go

@@ -0,0 +1,138 @@
+// Copyright 2020 The Bazel Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package chdir provides an init function that changes the current working
+// directory to RunDir when the test executable is started by Bazel
+// (when TEST_SRCDIR and TEST_WORKSPACE are set).
+//
+// This hides a difference between Bazel and 'go test': 'go test' starts test
+// executables in the package source directory, while Bazel starts test
+// executables in a directory made to look like the repository root directory.
+// Tests frequently refer to testdata files using paths relative to their
+// package directory, so open source tests frequently break unless they're
+// written with Bazel specifically in mind (using go/runfiles).
+//
+// For this init function to work, it must be called before init functions
+// in all user packages.
+//
+// In Go 1.20 and earlier, the package initialization order was underspecified,
+// other than a requirement that each package is initialized after all its
+// transitively imported packages. We relied on the linker initializing
+// packages in the order their imports appeared in source, so we import
+// bzltestutil (and transitively, this package) from the generated test main
+// before other packages.
+//
+// In Go 1.21, the package initialization order was clarified, and the
+// linker implementation was changed. See
+// https://go.dev/ref/spec#Program_initialization or
+// https://go.dev/doc/go1.21#language.
+//
+// > Given the list of all packages, sorted by import path, in each step the
+// > first uninitialized package in the list for which all imported packages
+// > (if any) are already initialized is initialized. This step is repeated
+// > until all packages are initialized.
+//
+// To ensure this package is initialized before user code without injecting
+// edges into the dependency graph, we implement the following hack:
+//
+// 1. Add the prefix '+initfirst/' to this package's path with the 'importmap'
+//    attribute. '+' is the first allowed character that sorts higher than
+//    letters. Because we're using 'importmap' and not 'importpath', this
+//    package may be imported in .go files without the prefix.
+// 2. Put this init function in a separate package that only imports "os".
+//    Previously, this function was in bzltestutil, but bzltest util imports
+//    several other std packages may be get initialized later. For example,
+//    the "sync" package is initialized after a user package named
+//    "github.com/a/b" that only imports "os", and because bzltestutil imports
+//    "sync", it would get initialized even later. A user package that imports
+//    nothing may still be initialized before "os", but we assume "os"
+//    is needed to observe the current directory.
+package chdir
+
+// This package should import nothing other than "os"
+// and packages imported by "os".
+import (
+	"os"
+	"runtime"
+)
+
+var (
+	// Initialized by linker.
+	RunDir string
+
+	// Initial working directory.
+	TestExecDir string
+)
+
+func init() {
+	var err error
+	TestExecDir, err = os.Getwd()
+	if err != nil {
+		panic(err)
+	}
+
+	// Check if we're being run by Bazel and change directories if so.
+	// TEST_SRCDIR and TEST_WORKSPACE are set by the Bazel test runner, so that makes a decent proxy.
+	testSrcDir, hasSrcDir := os.LookupEnv("TEST_SRCDIR")
+	testWorkspace, hasWorkspace := os.LookupEnv("TEST_WORKSPACE")
+	if hasSrcDir && hasWorkspace && RunDir != "" {
+		abs := RunDir
+		if !filepathIsAbs(RunDir) {
+			abs = filepathJoin(testSrcDir, testWorkspace, RunDir)
+		}
+		err := os.Chdir(abs)
+		// Ignore the Chdir err when on Windows, since it might have have runfiles symlinks.
+		// https://github.com/bazelbuild/rules_go/pull/1721#issuecomment-422145904
+		if err != nil && runtime.GOOS != "windows" {
+			panic("could not change to test directory: " + err.Error())
+		}
+		if err == nil {
+			os.Setenv("PWD", abs)
+		}
+	}
+}
+
+func filepathIsAbs(path string) bool {
+	if runtime.GOOS == "windows" {
+		// Drive-letter path
+		if len(path) >= 3 &&
+			('A' <= path[0] && path[0] <= 'Z' || 'a' <= path[0] && path[0] <= 'z') &&
+			path[1] == ':' &&
+			(path[2] == '\\' || path[2] == '/') {
+			return true
+		}
+
+		// UNC path
+		if len(path) >= 2 && path[0] == '\\' && path[1] == '\\' {
+			return true
+		}
+		return false
+	}
+
+	return len(path) > 0 && path[0] == '/'
+}
+
+func filepathJoin(base string, parts ...string) string {
+	n := len(base)
+	for _, part := range parts {
+		n += 1 + len(part)
+	}
+	buf := make([]byte, 0, n)
+	buf = append(buf, []byte(base)...)
+	for _, part := range parts {
+		buf = append(buf, os.PathSeparator)
+		buf = append(buf, []byte(part)...)
+	}
+	return string(buf)
+}

go/tools/bzltestutil/wrap.go

@@ -27,6 +27,8 @@ import (
 	"strconv"
 	"strings"
 	"sync"
+
+	"github.com/bazelbuild/rules_go/go/tools/bzltestutil/chdir"
 )
 
 // TestWrapperAbnormalExit is used by Wrap to indicate the child
@@ -117,8 +119,8 @@ func Wrap(pkg string) error {
 		args = append([]string{"-test.v"}, args...)
 	}
 	exePath := os.Args[0]
-	if !filepath.IsAbs(exePath) && strings.ContainsRune(exePath, filepath.Separator) && testExecDir != "" {
-		exePath = filepath.Join(testExecDir, exePath)
+	if !filepath.IsAbs(exePath) && strings.ContainsRune(exePath, filepath.Separator) && chdir.TestExecDir != "" {
+		exePath = filepath.Join(chdir.TestExecDir, exePath)
 	}
 	cmd := exec.Command(exePath, args...)
 	cmd.Env = append(os.Environ(), "GO_TEST_WRAP=0")