[PATCH 2/2] gdb/c++: Detect ambiguous variables in imported namespaces

[Bruno Larsen <blarsen@redhat.com>]

When running gdb.cp/nsusing.cc and stopping at line 17, we can ask GDB
to print x and get a compiler-dependent answer. Using gcc 12.2.1, GDB
will print M::x, and using clang 16.0.0 prints N::x. Not only is this
behavior confusing to users, it is also not consistent with compiler
behaviors, which would warn that using x is ambiguous at this point.

This commit makes it so instead of exiting early when finding any symbol
with the correct name, GDB continues searching through include
directives until it finds another symbol with the same name but a
different mangled name - returning an ambiguous variable - or goes
through all imported namespaces and returns zero or one matching symbols.

The commit also changes gdb.cp/nsusing.exp to test the ambiguous
detection.
---
 gdb/cp-namespace.c               | 35 ++++++++++++++++++++++++++++----
 gdb/testsuite/gdb.cp/nsusing.exp | 19 +++++++++++++----
 2 files changed, 46 insertions(+), 8 deletions(-)

diff --git a/gdb/cp-namespace.c b/gdb/cp-namespace.c
index c1b6978b7c8..7a07a8dbe75 100644
--- a/gdb/cp-namespace.c
+++ b/gdb/cp-namespace.c
@@ -383,6 +383,8 @@ cp_lookup_symbol_via_imports (const char *scope,
 {
   struct using_direct *current;
   struct block_symbol sym = {};
+  struct block_symbol saved_sym = {};
+  const char* sym_name = nullptr;
   int len;
   int directive_match;
 
@@ -392,7 +394,11 @@ cp_lookup_symbol_via_imports (const char *scope,
 					 block, domain, 1);
 
   if (sym.symbol != NULL)
-    return sym;
+    {
+      saved_sym = sym;
+      sym_name = saved_sym.symbol->m_name;
+      sym = {};
+    }
 
   /* Due to a GCC bug, we need to know the boundaries of the current block
      to know if a certain using directive is valid.  */
@@ -446,7 +452,16 @@ cp_lookup_symbol_via_imports (const char *scope,
 	  if (declaration_only || sym.symbol != NULL || current->declaration)
 	    {
 	      if (sym.symbol != NULL)
-		return sym;
+		{
+		  if(sym_name == nullptr)
+		    {
+		      saved_sym = sym;
+		      sym_name = saved_sym.symbol->m_name;
+		      sym = {};
+		    }
+		  else if (strcmp(sym_name, sym.symbol->m_name) != 0)
+		    error (_("reference to \"%s\" is ambiguous"), name);
+		}
 
 	      continue;
 	    }
@@ -479,11 +494,23 @@ cp_lookup_symbol_via_imports (const char *scope,
 	    }
 
 	  if (sym.symbol != NULL)
-	    return sym;
+	    {
+	      if(sym_name == nullptr)
+		{
+		  saved_sym = sym;
+		  sym_name = saved_sym.symbol->m_name;
+		  sym = {};
+		}
+	      else if (strcmp(sym_name, sym.symbol->m_name) != 0)
+		error (_("reference to \"%s\" is ambiguous"), name);
+	    }
 	}
     }
 
-  return {};
+  if (sym_name != nullptr)
+    return saved_sym;
+  else
+    return {};
 }
 
 /* Helper function that searches an array of symbols for one named NAME.  */
diff --git a/gdb/testsuite/gdb.cp/nsusing.exp b/gdb/testsuite/gdb.cp/nsusing.exp
index bce6e30adc1..363ae862953 100644
--- a/gdb/testsuite/gdb.cp/nsusing.exp
+++ b/gdb/testsuite/gdb.cp/nsusing.exp
@@ -123,15 +123,26 @@ if { [test_compiler_info {gcc-[0-3]-*}] ||
     return
 }
 
+    # GCC doesn't properly set the decl_line for namespaces, so GDB believes
+    # that both using directives are valid as long as we are in this scope.
+exp_internal 1
 gdb_test_multiple "print x" "print x, before using statement" {
     -re -wrap "No symbol .x. in current context.*" {
 	pass $gdb_test_name
     }
-    # GCC doesn't properly set the decl_line for namespaces, so GDB believes
-    # that the "using namespace M" line has already passed at this point.
-    -re -wrap "= 911.*" {
+    -re -wrap "reference to .x. is ambiguous.*" {
 	xfail $gdb_test_name
     }
 }
+exp_internal 0
 gdb_test "next" ".*" "using namespace M"
-gdb_test "print x" "= 911" "print x, only using M"
+gdb_test_multiple "print x" "print x, only using M" {
+    -re -wrap "= 911.*" {
+	pass $gdb_test_name
+    }
+    -re -wrap "reference to .x. is ambiguous.*" {
+	xfail $gdb_test_name
+    }
+}
+gdb_test "next" ".*" "using namespace N"
+gdb_test "print x"  "reference to .x. is ambiguous" "print x, with M and N"
-- 
2.37.3