x/text: fix nil dereference in gotext extract

Ident.Obj may be nil if the referenced declaration is in another file.

Fixes golang/go#60555

Change-Id: I730af89c7f52540b305b3da8c19448d089e9744c
Reviewed-on: https://go-review.googlesource.com/c/text/+/545055
Reviewed-by: Emmanuel Odeke <[email protected]>
Reviewed-by: Junyang Shao <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Sean Liao <[email protected]>
Auto-Submit: Emmanuel Odeke <[email protected]>
Reviewed-by: Michael Knyszek <[email protected]>

Author: drakkan

message/pipeline/extract.go

@@ -597,9 +597,13 @@ func (px packageExtracter) handleCall(call *ast.CallExpr) bool {
 	key := []string{}
 	if ident, ok := format.(*ast.Ident); ok {
 		key = append(key, ident.Name)
-		if v, ok := ident.Obj.Decl.(*ast.ValueSpec); ok && v.Comment != nil {
-			// TODO: get comment above ValueSpec as well
-			comment = v.Comment.Text()
+		// Ident.Obj may be nil if the referenced declaration is in another
+		// file.
+		if ident.Obj != nil {
+			if v, ok := ident.Obj.Decl.(*ast.ValueSpec); ok && v.Comment != nil {
+				// TODO: get comment above ValueSpec as well
+				comment = v.Comment.Text()
+			}
 		}
 	}
 	if c := px.getComment(call.Args[0]); c != "" {

message/pipeline/testdata/test60555/catalog_gen.go

@@ -0,0 +1,15 @@
+{
+    "language": "en-US",
+    "messages": [
+        {
+            "id": [
+                "testMessage",
+                "Test message"
+            ],
+            "key": "Test message",
+            "message": "Test message",
+            "translation": "",
+            "position": "testdata/test60555/main.go:17:10"
+        }
+    ]
+}

message/pipeline/testdata/test60555/extracted.gotext.json.want

@@ -0,0 +1,18 @@
+// Copyright 2025 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"golang.org/x/text/language"
+	"golang.org/x/text/message"
+)
+
+// Ensures that we can catch any regressions with nil dereferences
+// from const declarations in other files within the same package.
+// See issue https://golang.org/issues/60555
+func main() {
+	p := message.NewPrinter(language.English)
+	p.Printf(testMessage)
+}

message/pipeline/testdata/test60555/main.go

@@ -0,0 +1,7 @@
+// Copyright 2025 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+const testMessage = "Test message"