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 #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 #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>

1 files changed, 11 insertions, 11 deletions

diff --git a/src/cmd/link/link_test.go b/src/cmd/link/link_test.go
index 4dca2e20d6..b4ef9ada17 100644
--- a/src/cmd/link/link_test.go
+++ b/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)