resolve: passAsFile importcfg_entries (dynamic-mode link drv exceeds MAX_ARG_STRLEN on torture)

go/go2nix/pkg/resolve/builder.go

@@ -47,9 +47,9 @@ func compileScript(go2nixBin string) string {
 	b.WriteString("export HOME=\"$TMPDIR\"\n")
 	b.WriteString("mkdir -p \"$out\"\n\n")
 
-	// Write importcfg from env var (placeholders resolved by Nix at build time).
-	// Use absolute path since compile-package changes CWD to srcdir.
-	b.WriteString("printf '%s\\n' \"$importcfg_entries\" > \"$NIX_BUILD_TOP/importcfg\"\n\n")
+	// Write importcfg from passAsFile (placeholders resolved by Nix at build
+	// time). passAsFile keeps the derivation's exec env under MAX_ARG_STRLEN.
+	b.WriteString("cat \"$importcfg_entriesPath\" > \"$NIX_BUILD_TOP/importcfg\"\n\n")
 
 	// Write compile manifest from env var (JSON generated at derivation creation time).
 	// Replace @@IMPORTCFG@@ placeholder with the actual importcfg path so that
@@ -83,8 +83,9 @@ func linkScript(goStorePath, pname, buildMode string) string {
 	b.WriteString("export HOME=\"$TMPDIR\"\n")
 	b.WriteString("mkdir -p \"$out/bin\"\n\n")
 
-	// Write importcfg for all transitive deps
-	b.WriteString("printf '%s\\n' \"$importcfg_entries\" > \"$NIX_BUILD_TOP/importcfg\"\n\n")
+	// Write importcfg for all transitive deps. passAsFile keeps the exec
+	// env under MAX_ARG_STRLEN — torture's full closure is ~400KB.
+	b.WriteString("cat \"$importcfg_entriesPath\" > \"$NIX_BUILD_TOP/importcfg\"\n\n")
 
 	// Set GOROOT so the linker embeds it as runtime.defaultGOROOT,
 	// enabling runtime.GOROOT() in the resulting binary.

go/go2nix/pkg/resolve/builder_test.go

@@ -87,8 +87,8 @@ func TestCompileScript(t *testing.T) {
 	if !strings.Contains(script, "compile-package") {
 		t.Error("missing compile-package call")
 	}
-	if !strings.Contains(script, "$importcfg_entries") {
-		t.Error("missing importcfg_entries reference")
+	if !strings.Contains(script, "$importcfg_entriesPath") {
+		t.Error("missing importcfg_entriesPath reference")
 	}
 	if !strings.Contains(script, "${compileManifestJSON//@@IMPORTCFG@@/$NIX_BUILD_TOP/importcfg}") {
 		t.Error("missing compileManifestJSON with @@IMPORTCFG@@ expansion")
@@ -331,9 +331,9 @@ func TestBuildImportcfgMissingDrvPath(t *testing.T) {
 	}
 }
 
-// TestImportcfgEntriesBashWrite verifies that the multi-line importcfg_entries
-// env var is correctly written to a file by the bash printf in both
-// compileScript and linkScript.
+// TestImportcfgEntriesBashWrite verifies that the importcfg_entries content
+// (delivered via passAsFile) is correctly copied to NIX_BUILD_TOP/importcfg
+// by the bash snippet in both compileScript and linkScript.
 func TestImportcfgEntriesBashWrite(t *testing.T) {
 	entries := strings.Join([]string{
 		"packagefile fmt=/nix/store/stdlib/fmt.a",
@@ -342,13 +342,18 @@ func TestImportcfgEntriesBashWrite(t *testing.T) {
 	}, "\n")
 
 	tmpDir := t.TempDir()
+	inFile := filepath.Join(tmpDir, "passAsFile-importcfg_entries")
 	outFile := filepath.Join(tmpDir, "importcfg")
+	if err := os.WriteFile(inFile, []byte(entries), 0o644); err != nil {
+		t.Fatal(err)
+	}
 
 	// Run the same bash snippet used by both compileScript and linkScript.
-	script := `printf '%s\n' "$importcfg_entries" > "$outfile"`
+	script := `cat "$importcfg_entriesPath" > "$outfile"`
 	cmd := exec.Command("bash", "-c", script)
 	cmd.Env = []string{
-		"importcfg_entries=" + entries,
+		"PATH=" + os.Getenv("PATH"),
+		"importcfg_entriesPath=" + inFile,
 		"outfile=" + outFile,
 	}
 	if out, err := cmd.CombinedOutput(); err != nil {

go/go2nix/pkg/resolve/resolve.go

@@ -685,6 +685,7 @@ func buildPackageDrv(
 		return nil, fmt.Errorf("marshaling compile manifest: %w", err)
 	}
 	drv.SetEnv("compileManifestJSON", string(manifestJSON))
+	drv.SetEnv("passAsFile", "importcfg_entries")
 
 	if pkg.GoVersion != "" {
 		drv.SetEnv("goVersion", compile.LangVersion(pkg.GoVersion))
@@ -1030,6 +1031,7 @@ func buildLinkDrv(
 	}
 
 	drv.SetEnv("importcfg_entries", strings.Join(importcfgEntries, "\n"))
+	drv.SetEnv("passAsFile", "importcfg_entries")
 	drv.SetEnv("ldflags", cfg.LDFlags)
 
 	// Propagate sanitizer flags (-race, -msan, -asan) from gcflags to the