Go patch committed: Better error message for unknown package name

[Ian Lance Taylor via Gcc-patches]

This patch to the Go frontend gives a  better error message for an
unknown package name, saying "undefined reference" rather than
"expected package".  This requires updating a test.  This fixes
https://go.dev/issue/51237.  Bootstrapped and ran Go testsuite on
x86_64-pc-linux-gnu.  Committed to mainline.

Ian

db1256cfb4620c4d52175002940347d399148502
diff --git a/gcc/go/gofrontend/MERGE b/gcc/go/gofrontend/MERGE
index 7b1d3011fff..461e2fdf271 100644
--- a/gcc/go/gofrontend/MERGE
+++ b/gcc/go/gofrontend/MERGE
@@ -1,4 +1,4 @@
-6479d5976c5d848ec6f5843041275723a00006b0
+a209dca9ec918535977dcab99fd9bb60986ffacd
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.
diff --git a/gcc/go/gofrontend/parse.cc b/gcc/go/gofrontend/parse.cc
index a3c6f630a09..c93d82bba39 100644
--- a/gcc/go/gofrontend/parse.cc
+++ b/gcc/go/gofrontend/parse.cc
@@ -191,7 +191,11 @@ Parse::qualified_ident(std::string* pname, Named_object** 
ppackage)
   Named_object* package = this->gogo_->lookup(name, NULL);
   if (package == NULL || !package->is_package())
     {
-      go_error_at(this->location(), "expected package");
+      if (package == NULL)
+       go_error_at(this->location(), "reference to undefined name %qs",
+                   Gogo::message_name(name).c_str());
+      else
+       go_error_at(this->location(), "expected package");
       // We expect . IDENTIFIER; skip both.
       if (this->advance_token()->is_identifier())
        this->advance_token();
diff --git a/gcc/testsuite/go.test/test/fixedbugs/issue27938.go 
b/gcc/testsuite/go.test/test/fixedbugs/issue27938.go
index ed974e642df..aecc67678ac 100644
--- a/gcc/testsuite/go.test/test/fixedbugs/issue27938.go
+++ b/gcc/testsuite/go.test/test/fixedbugs/issue27938.go
@@ -11,13 +11,13 @@
 package p
 
 type _ struct {
-       F sync.Mutex // ERROR "undefined: sync|expected package"
+       F sync.Mutex // ERROR "undefined: sync|expected package|reference to 
undefined name"
 }
 
 type _ struct {
-       sync.Mutex // ERROR "undefined: sync|expected package"
+       sync.Mutex // ERROR "undefined: sync|expected package|reference to 
undefined name"
 }
 
 type _ interface {
-       sync.Mutex // ERROR "undefined: sync|expected package|expected 
signature or type name"
+       sync.Mutex // ERROR "undefined: sync|expected package|expected 
signature or type name|reference to undefined name"
 }