cache macOS sysroot discovery

Author: cpunion

internal/crosscompile/crosscompile.go

@@ -9,6 +9,7 @@ import (
 	"path/filepath"
 	"runtime"
 	"strings"
+	"sync"
 
 	"github.com/goplus/llgo/internal/crosscompile/compile"
 	"github.com/goplus/llgo/internal/env"
@@ -96,14 +97,35 @@ func getCanonicalArchName(triple string) string {
 	return arch
 }
 
-// getMacOSSysroot returns the macOS SDK path using xcrun
+var (
+	macOSSysrootMu     sync.Mutex
+	macOSSysrootCached string
+	macOSSysrootLookup = func() (string, error) {
+		cmd := exec.Command("xcrun", "--sdk", "macosx", "--show-sdk-path")
+		output, err := cmd.Output()
+		if err != nil {
+			return "", err
+		}
+		return strings.TrimSpace(string(output)), nil
+	}
+)
+
+// getMacOSSysroot returns the macOS SDK path using xcrun.
 func getMacOSSysroot() (string, error) {
-	cmd := exec.Command("xcrun", "--sdk", "macosx", "--show-sdk-path")
-	output, err := cmd.Output()
+	macOSSysrootMu.Lock()
+	defer macOSSysrootMu.Unlock()
+	if macOSSysrootCached != "" {
+		return macOSSysrootCached, nil
+	}
+
+	sysroot, err := macOSSysrootLookup()
 	if err != nil {
 		return "", err
 	}
-	return strings.TrimSpace(string(output)), nil
+	if sysroot != "" {
+		macOSSysrootCached = sysroot
+	}
+	return sysroot, nil
 }
 
 // getESPClangRoot returns the ESP Clang root directory, checking LLGoROOT first,

internal/crosscompile/crosscompile_test.go

@@ -4,6 +4,7 @@
 package crosscompile
 
 import (
+	"errors"
 	"os"
 	"path/filepath"
 	"runtime"
@@ -21,6 +22,69 @@ const (
 	libPrefix         = "-L"
 )
 
+func resetMacOSSysrootForTest(t *testing.T) {
+	t.Helper()
+	macOSSysrootMu.Lock()
+	oldCached := macOSSysrootCached
+	oldLookup := macOSSysrootLookup
+	macOSSysrootCached = ""
+	macOSSysrootMu.Unlock()
+	t.Cleanup(func() {
+		macOSSysrootMu.Lock()
+		macOSSysrootCached = oldCached
+		macOSSysrootLookup = oldLookup
+		macOSSysrootMu.Unlock()
+	})
+}
+
+func TestGetMacOSSysrootCachesSuccess(t *testing.T) {
+	resetMacOSSysrootForTest(t)
+	calls := 0
+	macOSSysrootLookup = func() (string, error) {
+		calls++
+		return "/test/sdk", nil
+	}
+	first, err := getMacOSSysroot()
+	if err != nil {
+		t.Fatalf("first getMacOSSysroot: %v", err)
+	}
+	second, err := getMacOSSysroot()
+	if err != nil {
+		t.Fatalf("second getMacOSSysroot: %v", err)
+	}
+	if first != "/test/sdk" || second != "/test/sdk" {
+		t.Fatalf("sysroots = %q, %q; want cached /test/sdk", first, second)
+	}
+	if calls != 1 {
+		t.Fatalf("lookup calls = %d, want 1", calls)
+	}
+}
+
+func TestGetMacOSSysrootDoesNotCacheErrors(t *testing.T) {
+	resetMacOSSysrootForTest(t)
+	calls := 0
+	macOSSysrootLookup = func() (string, error) {
+		calls++
+		if calls == 1 {
+			return "", errors.New("temporary xcrun failure")
+		}
+		return "/test/sdk", nil
+	}
+	if _, err := getMacOSSysroot(); err == nil {
+		t.Fatal("first getMacOSSysroot succeeded, want error")
+	}
+	got, err := getMacOSSysroot()
+	if err != nil {
+		t.Fatalf("second getMacOSSysroot: %v", err)
+	}
+	if got != "/test/sdk" {
+		t.Fatalf("sysroot = %q, want /test/sdk", got)
+	}
+	if calls != 2 {
+		t.Fatalf("lookup calls = %d, want retry after error", calls)
+	}
+}
+
 func TestUseCrossCompileSDK(t *testing.T) {
 	// Skip long-running tests unless explicitly enabled
 	if testing.Short() {