go_test: change directory before use init() functions run

BUILD.bazel

@@ -33,6 +33,7 @@ load(
 # gazelle:exclude go/tools/coverdata
 # gazelle:exclude go/tools/fetch_repo
 # gazelle:exclude go/tools/windows-testrunner
+# gazelle:exclude go/tools/testinit
 # gazelle:exclude go/tools/testwrapper
 # gazelle:go_naming_convention import_alias
 

go/private/rules/test.bzl

@@ -93,7 +93,6 @@ def _go_test_impl(ctx):
 
     main_go = go.declare_file(go, path = "testmain.go")
     arguments = go.builder_args(go, "gentestmain")
-    arguments.add("-rundir", run_dir)
     arguments.add("-output", main_go)
     if ctx.configuration.coverage_enabled:
         arguments.add("-coverage")
@@ -115,16 +114,16 @@ def _go_test_impl(ctx):
         mnemonic = "GoTestGenTest",
         executable = go.toolchain._builder,
         arguments = [arguments],
-        env = {
-            "RUNDIR": ctx.label.package,
-        },
     )
 
     test_gc_linkopts = gc_linkopts(ctx)
     if not go.mode.debug:
         # Disable symbol table and DWARF generation for test binaries.
         test_gc_linkopts.extend(["-s", "-w"])
 
+    # Link in the run_dir global for testinit
+    test_gc_linkopts.extend(["-X", "github.com/bazelbuild/rules_go/go/tools/testinit.RunDir=" + run_dir])
+
     # Now compile the test binary itself
     test_library = GoLibrary(
         name = go._ctx.label.name + "~testmain",
@@ -136,7 +135,7 @@ def _go_test_impl(ctx):
         is_main = True,
         resolve = None,
     )
-    test_deps = external_archive.direct + [external_archive]
+    test_deps = external_archive.direct + [external_archive] + ctx.attr._testmain_additional_deps
     if ctx.configuration.coverage_enabled:
         test_deps.append(go.coverdata)
     test_source = go.library_to_source(go, struct(
@@ -200,6 +199,10 @@ _go_test_kwargs = {
             default = ["@io_bazel_rules_go//go/tools/testwrapper:srcs"],
             allow_files = go_exts,
         ),
+        "_testmain_additional_deps": attr.label_list(
+            providers = [GoLibrary],
+            default = ["@io_bazel_rules_go//go/tools/testinit"],
+        ),
         # Workaround for bazelbuild/bazel#6293. See comment in lcov_merger.sh.
         "_lcov_merger": attr.label(
             executable = True,

go/tools/BUILD.bazel

@@ -6,6 +6,7 @@ filegroup(
         "//go/tools/bazel_testing:all_files",
         "//go/tools/builders:all_files",
         "//go/tools/coverdata:all_files",
+        "//go/tools/testinit:all_files",
         "//go/tools/testwrapper:all_files",
     ],
     visibility = ["//visibility:public"],

go/tools/builders/generate_test_main.go

@@ -25,7 +25,6 @@ import (
 	"go/parser"
 	"go/token"
 	"os"
-	"path/filepath"
 	"sort"
 	"strings"
 	"text/template"
@@ -50,7 +49,6 @@ type Example struct {
 
 // Cases holds template data.
 type Cases struct {
-	RunDir     string
 	Imports    []*Import
 	Tests      []TestCase
 	Benchmarks []TestCase
@@ -62,13 +60,19 @@ type Cases struct {
 
 const testMainTpl = `
 package main
+// This package must be initialized before packages being tested.
+// NOTE: this relies on the order of package initialization, which is the spec
+// is somewhat unclear about-- it only clearly guarantees that imported packages
+// are initialized before their importers, though in practice (and implied) it
+// also respects declaration order, which we're relying on here.
+import (
+	_ "github.com/bazelbuild/rules_go/go/tools/testinit"
+)
 import (
 	"flag"
 	"log"
 	"os"
 	"os/exec"
-	"path/filepath"
-	"runtime"
 	"strconv"
 	"testing"
 	"testing/internal/testdeps"
@@ -131,23 +135,6 @@ func main() {
 		}
 	}
 
-	// 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 := os.Getenv("TEST_SRCDIR")
-	testWorkspace := os.Getenv("TEST_WORKSPACE")
-	if testSrcdir != "" && testWorkspace != "" {
-		abs := filepath.Join(testSrcdir, testWorkspace, {{printf "%q" .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" {
-			log.Fatalf("could not change to test directory: %v", err)
-		}
-		if err == nil {
-			os.Setenv("PWD", abs)
-		}
-	}
-
 	m := testing.MainStart(testdeps.TestDeps{}, testsInShard(), benchmarks, examples)
 
 	if filter := os.Getenv("TESTBRIDGE_TEST_ONLY"); filter != "" {
@@ -183,7 +170,6 @@ func genTestMain(args []string) error {
 	sources := multiFlag{}
 	flags := flag.NewFlagSet("GoTestGenTest", flag.ExitOnError)
 	goenv := envFlags(flags)
-	runDir := flags.String("rundir", ".", "Path to directory where tests should run.")
 	out := flags.String("output", "", "output file to write. Defaults to stdout.")
 	coverage := flags.Bool("coverage", false, "whether coverage is supported")
 	pkgname := flags.String("pkgname", "", "package name of test")
@@ -235,7 +221,6 @@ func genTestMain(args []string) error {
 	}
 
 	cases := Cases{
-		RunDir:   strings.Replace(filepath.FromSlash(*runDir), `\`, `\\`, -1),
 		Coverage: *coverage,
 		Pkgname:  *pkgname,
 	}

go/tools/testinit/BUILD.bazel

@@ -0,0 +1,15 @@
+load("@io_bazel_rules_go//go/private/rules:library.bzl", "go_tool_library")
+
+go_tool_library(
+    name = "testinit",
+    srcs = ["testinit.go"],
+    importpath = "github.com/bazelbuild/rules_go/go/tools/testinit",
+    visibility = ["//visibility:public"],
+)
+
+filegroup(
+    name = "all_files",
+    testonly = True,
+    srcs = glob(["**"]),
+    visibility = ["//visibility:public"],
+)

go/tools/testinit/testinit.go

@@ -0,0 +1,56 @@
+// 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 testinit
+
+// This package must have no deps beyond Go SDK.
+import (
+	"log"
+	"os"
+	"path/filepath"
+	"runtime"
+)
+
+var (
+	// Initialized by linker.
+	RunDir string
+)
+
+// This initializer runs before any user packages.
+func init() {
+	// 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 !filepath.IsAbs(RunDir) {
+			abs = filepath.Join(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" {
+			log.Fatalf("could not change to test directory: %v", err)
+		}
+		if err == nil {
+			_ = os.Setenv("PWD", abs)
+		}
+	}
+
+	// Setup the bazel tmpdir as the go tmpdir.
+	if tmpDir, ok := os.LookupEnv("TEST_TMPDIR"); ok {
+		_ = os.Setenv("TMPDIR", tmpDir)
+	}
+}