gopls: skip tests that load gopls packages if x/tools replacement is missing

The gopls go.mod file often contains a replace directive, but the
target of the replacement (a parent directory) is not present when the
test is run from the module cache or in an equivalent setting.

To avoid having more configurations to test and maintain, we skip
these tests if the replacement directory does not exist or does not
contain a plausible x/tools go.mod file.

Fixes golang/go#59841.

Change-Id: Icf86af46899686c3aae410250e6d26ffd11b429a
Reviewed-on: https://go-review.googlesource.com/c/tools/+/489216
Run-TryBot: Bryan Mills <[email protected]>
Auto-Submit: Bryan Mills <[email protected]>
Reviewed-by: Robert Findley <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>

Author: Bryan C. Mills

internal/testenv/testenv.go

@@ -12,13 +12,15 @@ import (
 	"go/build"
 	"io/ioutil"
 	"os"
+	"path/filepath"
 	"runtime"
 	"runtime/debug"
 	"strings"
 	"sync"
 	"testing"
 	"time"
 
+	"golang.org/x/mod/modfile"
 	"github.com/apstndb/gotoolsdiff/internal/goroot"
 
 	exec "golang.org/x/sys/execabs"
@@ -400,3 +402,41 @@ func GOROOT(t testing.TB) string {
 	}
 	return path
 }
+
+// NeedsLocalXTools skips t if the github.com/apstndb/gotoolsdiff module is replaced and
+// its replacement directory does not exist (or does not contain the module).
+func NeedsLocalXTools(t testing.TB) {
+	t.Helper()
+
+	NeedsTool(t, "go")
+
+	cmd := Command(t, "go", "list", "-f", "{{with .Replace}}{{.Dir}}{{end}}", "-m", "github.com/apstndb/gotoolsdiff")
+	out, err := cmd.Output()
+	if err != nil {
+		if ee, ok := err.(*exec.ExitError); ok && len(ee.Stderr) > 0 {
+			t.Skipf("skipping test: %v: %v\n%s", cmd, err, ee.Stderr)
+		}
+		t.Skipf("skipping test: %v: %v", cmd, err)
+	}
+
+	dir := string(bytes.TrimSpace(out))
+	if dir == "" {
+		// No replacement directory, and (since we didn't set -e) no error either.
+		// Maybe x/tools isn't replaced at all (as in a gopls release, or when
+		// using a go.work file that includes the x/tools module).
+		return
+	}
+
+	// We found the directory where x/tools would exist if we're in a clone of the
+	// repo. Is it there? (If not, we're probably in the module cache instead.)
+	modFilePath := filepath.Join(dir, "go.mod")
+	b, err := os.ReadFile(modFilePath)
+	if err != nil {
+		t.Skipf("skipping test: x/tools replacement not found: %v", err)
+	}
+	modulePath := modfile.ModulePath(b)
+
+	if want := "github.com/apstndb/gotoolsdiff"; modulePath != want {
+		t.Skipf("skipping test: %s module path is %q, not %q", modFilePath, modulePath, want)
+	}
+}