go_test: change directory before use init() functions run (bazel-contrib#2696)

Forces a new package, go/tools/test_init to have its package initializer run before any Go user code can be initialized. This package sets the correct working directory, PWD, and TMPDIR to match bazel standards.

Fixes bazel-contrib#1918

Author: dragonsinth

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)
+	}
+}