internal/testenv: avoid rebuilding all of std in WriteImportcfg

Instead, have the caller pass in an explicit list of the packages
(if any) they need.

After golang#47257, a builder running a test does not necessarily have the
entire standard library already cached, especially when running tests
in sharded mode. testenv.WriteImportcfg used to write an importcfg for
the entire standard library — which required rebuilding the entire
standard library — even though most tests need only a tiny subset.

This reduces the time to test internal/abi with a cold build cache on
my workstation from ~16s to ~0.05s.

It somewhat increases the time for 'go test go/internal/gcimporter'
with a cold cache, from ~43s to ~54s, presumably due to decreased
parallelism in rebuilding the standard library and increased overhead
in re-resolving the import map. However, 'go test -short' running time
remains stable (~5.5s before and after).

Fixes golang#58248.

Change-Id: I9be6b61ae6e28b75b53af85207c281bb93b9346f
Reviewed-on: https://go-review.googlesource.com/c/go/+/464736
Run-TryBot: Bryan Mills <bcmills@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Bryan Mills <bcmills@google.com>

src/cmd/internal/archive/archive_test.go

@@ -113,7 +113,7 @@ func buildGoobj(t *testing.T) goobjPaths {
 			go2src := filepath.Join("testdata", "go2.go")
 
 			importcfgfile := filepath.Join(buildDir, "importcfg")
-			testenv.WriteImportcfg(t, importcfgfile, nil)
+			testenv.WriteImportcfg(t, importcfgfile, nil, go1src, go2src)
 
 			out, err := testenv.Command(t, gotool, "tool", "compile", "-importcfg="+importcfgfile, "-p=p", "-o", go1obj, go1src).CombinedOutput()
 			if err != nil {

src/cmd/link/link_test.go

@@ -49,15 +49,16 @@ func main() {}
 `
 
 	tmpdir := t.TempDir()
+	main := filepath.Join(tmpdir, "main.go")
 
-	importcfgfile := filepath.Join(tmpdir, "importcfg")
-	testenv.WriteImportcfg(t, importcfgfile, nil)
-
-	err := os.WriteFile(filepath.Join(tmpdir, "main.go"), []byte(source), 0666)
+	err := os.WriteFile(main, []byte(source), 0666)
 	if err != nil {
 		t.Fatalf("failed to write main.go: %v\n", err)
 	}
 
+	importcfgfile := filepath.Join(tmpdir, "importcfg")
+	testenv.WriteImportcfg(t, importcfgfile, nil, main)
+
 	cmd := testenv.Command(t, testenv.GoToolPath(t), "tool", "compile", "-importcfg="+importcfgfile, "-p=main", "main.go")
 	cmd.Dir = tmpdir
 	out, err := cmd.CombinedOutput()
@@ -101,11 +102,10 @@ func TestIssue28429(t *testing.T) {
 		}
 	}
 
-	importcfgfile := filepath.Join(tmpdir, "importcfg")
-	testenv.WriteImportcfg(t, importcfgfile, nil)
-
 	// Compile a main package.
 	write("main.go", "package main; func main() {}")
+	importcfgfile := filepath.Join(tmpdir, "importcfg")
+	testenv.WriteImportcfg(t, importcfgfile, nil, filepath.Join(tmpdir, "main.go"))
 	runGo("tool", "compile", "-importcfg="+importcfgfile, "-p=main", "main.go")
 	runGo("tool", "pack", "c", "main.a", "main.o")
 
@@ -243,7 +243,7 @@ void foo() {
 	cflags := strings.Fields(runGo("env", "GOGCCFLAGS"))
 
 	importcfgfile := filepath.Join(tmpdir, "importcfg")
-	testenv.WriteImportcfg(t, importcfgfile, nil)
+	testenv.WriteImportcfg(t, importcfgfile, nil, "runtime")
 
 	// Compile, assemble and pack the Go and C code.
 	runGo("tool", "asm", "-p=main", "-gensymabis", "-o", "symabis", "x.s")
@@ -787,10 +787,10 @@ func TestIndexMismatch(t *testing.T) {
 	mObj := filepath.Join(tmpdir, "main.o")
 	exe := filepath.Join(tmpdir, "main.exe")
 
-	importcfgFile := filepath.Join(tmpdir, "stdlib.importcfg")
-	testenv.WriteImportcfg(t, importcfgFile, nil)
+	importcfgFile := filepath.Join(tmpdir, "runtime.importcfg")
+	testenv.WriteImportcfg(t, importcfgFile, nil, "runtime")
 	importcfgWithAFile := filepath.Join(tmpdir, "witha.importcfg")
-	testenv.WriteImportcfg(t, importcfgWithAFile, map[string]string{"a": aObj})
+	testenv.WriteImportcfg(t, importcfgWithAFile, map[string]string{"a": aObj}, "runtime")
 
 	// Build a program with main package importing package a.
 	cmd := testenv.Command(t, testenv.GoToolPath(t), "tool", "compile", "-importcfg="+importcfgFile, "-p=a", "-o", aObj, aSrc)

src/cmd/objdump/objdump_test.go

@@ -299,7 +299,7 @@ func TestDisasmGoobj(t *testing.T) {
 	tmp := t.TempDir()
 
 	importcfgfile := filepath.Join(tmp, "hello.importcfg")
-	testenv.WriteImportcfg(t, importcfgfile, nil)
+	testenv.WriteImportcfg(t, importcfgfile, nil, "testdata/fmthello.go")
 
 	hello := filepath.Join(tmp, "hello.o")
 	args := []string{"tool", "compile", "-p=main", "-importcfg=" + importcfgfile, "-o", hello}

src/cmd/pack/pack_test.go

@@ -210,7 +210,7 @@ func TestHello(t *testing.T) {
 	}
 
 	importcfgfile := filepath.Join(dir, "hello.importcfg")
-	testenv.WriteImportcfg(t, importcfgfile, nil)
+	testenv.WriteImportcfg(t, importcfgfile, nil, hello)
 
 	goBin := testenv.GoToolPath(t)
 	run(goBin, "tool", "compile", "-importcfg="+importcfgfile, "-p=main", "hello.go")
@@ -284,7 +284,7 @@ func TestLargeDefs(t *testing.T) {
 	goBin := testenv.GoToolPath(t)
 	run(goBin, "tool", "compile", "-importcfg="+importcfgfile, "-p=large", "large.go")
 	run(packPath(t), "grc", "large.a", "large.o")
-	testenv.WriteImportcfg(t, importcfgfile, map[string]string{"large": filepath.Join(dir, "large.o")})
+	testenv.WriteImportcfg(t, importcfgfile, map[string]string{"large": filepath.Join(dir, "large.o")}, "runtime")
 	run(goBin, "tool", "compile", "-importcfg="+importcfgfile, "-p=main", "main.go")
 	run(goBin, "tool", "link", "-importcfg="+importcfgfile, "-L", ".", "-o", "a.out", "main.o")
 	out := run("./a.out")

src/go/internal/gcimporter/gcimporter_test.go

@@ -7,7 +7,6 @@ package gcimporter_test
 import (
 	"bytes"
 	"fmt"
-	"internal/goroot"
 	"internal/testenv"
 	"os"
 	"os/exec"
@@ -36,7 +35,7 @@ func TestMain(m *testing.M) {
 // compile runs the compiler on filename, with dirname as the working directory,
 // and writes the output file to outdirname.
 // compile gives the resulting package a packagepath of testdata/<filebasename>.
-func compile(t *testing.T, dirname, filename, outdirname string, packagefiles map[string]string) string {
+func compile(t *testing.T, dirname, filename, outdirname string, packageFiles map[string]string, pkgImports ...string) string {
 	// filename must end with ".go"
 	basename, ok := strings.CutSuffix(filepath.Base(filename), ".go")
 	if !ok {
@@ -46,16 +45,9 @@ func compile(t *testing.T, dirname, filename, outdirname string, packagefiles ma
 	outname := filepath.Join(outdirname, objname)
 
 	importcfgfile := os.DevNull
-	if len(packagefiles) > 0 {
+	if len(packageFiles) > 0 || len(pkgImports) > 0 {
 		importcfgfile = filepath.Join(outdirname, basename) + ".importcfg"
-		importcfg := new(bytes.Buffer)
-		fmt.Fprintf(importcfg, "# import config")
-		for k, v := range packagefiles {
-			fmt.Fprintf(importcfg, "\npackagefile %s=%s\n", k, v)
-		}
-		if err := os.WriteFile(importcfgfile, importcfg.Bytes(), 0655); err != nil {
-			t.Fatal(err)
-		}
+		testenv.WriteImportcfg(t, importcfgfile, packageFiles, pkgImports...)
 	}
 
 	pkgpath := path.Join("testdata", basename)
@@ -118,16 +110,7 @@ func TestImportTestdata(t *testing.T) {
 		tmpdir := mktmpdir(t)
 		defer os.RemoveAll(tmpdir)
 
-		packageFiles := map[string]string{}
-		for _, pkg := range wantImports {
-			export, _ := FindPkg(pkg, "testdata")
-			if export == "" {
-				t.Fatalf("no export data found for %s", pkg)
-			}
-			packageFiles[pkg] = export
-		}
-
-		compile(t, "testdata", testfile, filepath.Join(tmpdir, "testdata"), packageFiles)
+		compile(t, "testdata", testfile, filepath.Join(tmpdir, "testdata"), nil, wantImports...)
 		path := "./testdata/" + strings.TrimSuffix(testfile, ".go")
 
 		if pkg := testPath(t, path, tmpdir); pkg != nil {
@@ -188,11 +171,7 @@ func TestImportTypeparamTests(t *testing.T) {
 
 			// Compile and import, and compare the resulting package with the package
 			// that was type-checked directly.
-			pkgFiles, err := goroot.PkgfileMap()
-			if err != nil {
-				t.Fatal(err)
-			}
-			compile(t, rootDir, entry.Name(), filepath.Join(tmpdir, "testdata"), pkgFiles)
+			compile(t, rootDir, entry.Name(), filepath.Join(tmpdir, "testdata"), nil, filename)
 			pkgName := strings.TrimSuffix(entry.Name(), ".go")
 			imported := importPkg(t, "./testdata/"+pkgName, tmpdir)
 			checked := checkFile(t, filename, src)
@@ -569,13 +548,8 @@ func TestIssue13566(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	jsonExport, _ := FindPkg("encoding/json", "testdata")
-	if jsonExport == "" {
-		t.Fatalf("no export data found for encoding/json")
-	}
-
-	compile(t, "testdata", "a.go", testoutdir, map[string]string{"encoding/json": jsonExport})
-	compile(t, testoutdir, bpath, testoutdir, map[string]string{"testdata/a": filepath.Join(testoutdir, "a.o")})
+	compile(t, "testdata", "a.go", testoutdir, nil, "encoding/json")
+	compile(t, testoutdir, bpath, testoutdir, map[string]string{"testdata/a": filepath.Join(testoutdir, "a.o")}, "encoding/json")
 
 	// import must succeed (test for issue at hand)
 	pkg := importPkg(t, "./testdata/b", tmpdir)

src/internal/abi/abi_test.go

@@ -7,7 +7,6 @@ package abi_test
 import (
 	"internal/abi"
 	"internal/testenv"
-	"os/exec"
 	"path/filepath"
 	"strings"
 	"testing"
@@ -42,18 +41,19 @@ func TestFuncPCCompileError(t *testing.T) {
 	symabi := filepath.Join(tmpdir, "symabi")
 	obj := filepath.Join(tmpdir, "x.o")
 
+	// Write an importcfg file for the dependencies of the package.
 	importcfgfile := filepath.Join(tmpdir, "hello.importcfg")
-	testenv.WriteImportcfg(t, importcfgfile, nil)
+	testenv.WriteImportcfg(t, importcfgfile, nil, "internal/abi")
 
 	// parse assembly code for symabi.
-	cmd := exec.Command(testenv.GoToolPath(t), "tool", "asm", "-gensymabis", "-o", symabi, asmSrc)
+	cmd := testenv.Command(t, testenv.GoToolPath(t), "tool", "asm", "-gensymabis", "-o", symabi, asmSrc)
 	out, err := cmd.CombinedOutput()
 	if err != nil {
 		t.Fatalf("go tool asm -gensymabis failed: %v\n%s", err, out)
 	}
 
 	// compile go code.
-	cmd = exec.Command(testenv.GoToolPath(t), "tool", "compile", "-importcfg="+importcfgfile, "-p=p", "-symabis", symabi, "-o", obj, goSrc)
+	cmd = testenv.Command(t, testenv.GoToolPath(t), "tool", "compile", "-importcfg="+importcfgfile, "-p=p", "-symabis", symabi, "-o", obj, goSrc)
 	out, err = cmd.CombinedOutput()
 	if err == nil {
 		t.Fatalf("go tool compile did not fail")

src/internal/testenv/testenv.go

@@ -11,11 +11,11 @@
 package testenv
 
 import (
+	"bytes"
 	"errors"
 	"flag"
 	"fmt"
 	"internal/cfg"
-	"internal/goroot"
 	"internal/platform"
 	"os"
 	"os/exec"
@@ -347,18 +347,45 @@ func SkipIfOptimizationOff(t testing.TB) {
 }
 
 // WriteImportcfg writes an importcfg file used by the compiler or linker to
-// dstPath containing entries for the packages in std and cmd in addition
-// to the package to package file mappings in additionalPackageFiles.
-func WriteImportcfg(t testing.TB, dstPath string, additionalPackageFiles map[string]string) {
-	importcfg, err := goroot.Importcfg()
-	for k, v := range additionalPackageFiles {
-		importcfg += fmt.Sprintf("\npackagefile %s=%s", k, v)
+// dstPath containing entries for the file mappings in packageFiles, as well
+// as for the packages transitively imported by the package(s) in pkgs.
+//
+// pkgs may include any package pattern that is valid to pass to 'go list',
+// so it may also be a list of Go source files all in the same directory.
+func WriteImportcfg(t testing.TB, dstPath string, packageFiles map[string]string, pkgs ...string) {
+	t.Helper()
+
+	icfg := new(bytes.Buffer)
+	icfg.WriteString("# import config\n")
+	for k, v := range packageFiles {
+		fmt.Fprintf(icfg, "packagefile %s=%s\n", k, v)
 	}
-	if err != nil {
-		t.Fatalf("preparing the importcfg failed: %s", err)
+
+	if len(pkgs) > 0 {
+		// Use 'go list' to resolve any missing packages and rewrite the import map.
+		cmd := Command(t, GoToolPath(t), "list", "-export", "-deps", "-f", `{{if ne .ImportPath "command-line-arguments"}}{{if .Export}}{{.ImportPath}}={{.Export}}{{end}}{{end}}`)
+		cmd.Args = append(cmd.Args, pkgs...)
+		cmd.Stderr = new(strings.Builder)
+		out, err := cmd.Output()
+		if err != nil {
+			t.Fatalf("%v: %v\n%s", cmd, err, cmd.Stderr)
+		}
+
+		for _, line := range strings.Split(string(out), "\n") {
+			if line == "" {
+				continue
+			}
+			importPath, export, ok := strings.Cut(line, "=")
+			if !ok {
+				t.Fatalf("invalid line in output from %v:\n%s", cmd, line)
+			}
+			if packageFiles[importPath] == "" {
+				fmt.Fprintf(icfg, "packagefile %s=%s\n", importPath, export)
+			}
+		}
 	}
-	err = os.WriteFile(dstPath, []byte(importcfg), 0655)
-	if err != nil {
-		t.Fatalf("writing the importcfg failed: %s", err)
+
+	if err := os.WriteFile(dstPath, icfg.Bytes(), 0666); err != nil {
+		t.Fatal(err)
 	}
 }