[lldb][DataFormatter] Unwrap reference type when formatting std::unordered_map (#145872)

Desugar any potential references/typedefs before checking
`isStdTemplate`. Previously, the typename might've been:
```
const std::unordered_map<...> &
```
for references. This patch gets the pointee type before grabbing the
canonical type. `GetNonReferenceType` will unwrap typedefs too, so we
should always end up with a non-reference before we get to
`GetCanonicalType`.

#145847

Author: Michael137

lldb/source/Plugins/Language/CPlusPlus/LibCxxUnorderedMap.cpp

@@ -113,8 +113,10 @@ CompilerType lldb_private::formatters::LibcxxStdUnorderedMapSyntheticFrontEnd::
   // wraps a std::pair. Peel away the internal wrapper type - whose structure is
   // of no value to users, to expose the std::pair. This matches the structure
   // returned by the std::map synthetic provider.
-  if (isUnorderedMap(
-          m_backend.GetCompilerType().GetCanonicalType().GetTypeName())) {
+  if (isUnorderedMap(m_backend.GetCompilerType()
+                         .GetNonReferenceType()
+                         .GetCanonicalType()
+                         .GetTypeName())) {
     std::string name;
     CompilerType field_type =
         element_type.GetFieldAtIndex(0, name, nullptr, nullptr, nullptr);

lldb/test/API/functionalities/data-formatter/data-formatter-stl/libcxx/unordered_map/TestDataFormatterLibccUnorderedMap.py

@@ -9,6 +9,22 @@
 
 
 class LibcxxUnorderedMapDataFormatterTestCase(TestBase):
+    def check_reference(self, var_name: str, expected_type: str):
+        self.expect_var_path(
+            var_name,
+            summary="size=1",
+            type=expected_type,
+            children=[
+                ValueCheck(
+                    name="[0]",
+                    children=[
+                        ValueCheck(name="first", summary='"Hello"'),
+                        ValueCheck(name="second", summary='"World"'),
+                    ],
+                ),
+            ],
+        )
+
     @add_test_categories(["libc++"])
     def test_iterator_formatters(self):
         """Test that std::unordered_map related structures are formatted correctly when printed.
@@ -64,3 +80,20 @@ def test_iterator_formatters(self):
                 ValueCheck(name="second", summary='"Qux"'),
             ],
         )
+
+        lldbutil.continue_to_breakpoint(process, bkpt)
+
+        # Test references to std::unordered_map
+        self.check_reference("ref1", "const StringMapT &")
+        self.check_reference("ref2", "StringMapT &")
+        self.check_reference("ref3", "StringMapTRef")
+        self.check_reference("ref4", "const StringMapT &")
+        self.check_reference("ref5", "const StringMapT &&")
+        self.check_reference("ref6", "StringMapT &&")
+
+        # FIXME: we're getting this wrong.
+        self.expect_var_path(
+            "ref7",
+            summary="size=0",
+            type="const StringMapT *const &",
+        )

lldb/test/API/functionalities/data-formatter/data-formatter-stl/libcxx/unordered_map/main.cpp

@@ -3,6 +3,14 @@
 #include <unordered_map>
 
 using StringMapT = std::unordered_map<std::string, std::string>;
+using StringMapTRef = const StringMapT &;
+
+static void check_references(const StringMapT &ref1, StringMapT &ref2,
+                             StringMapTRef ref3, StringMapTRef &ref4,
+                             const StringMapT &&ref5, StringMapT &&ref6,
+                             const StringMapT *const &ref7) {
+  std::printf("Break here");
+}
 
 int main() {
   StringMapT string_map;
@@ -21,7 +29,12 @@ int main() {
     StringMapT::const_iterator const_baz = string_map.find("Baz");
     auto bucket_it = string_map.begin(string_map.bucket("Baz"));
     auto const_bucket_it = string_map.cbegin(string_map.bucket("Baz"));
+
     std::printf("Break here");
+
+    StringMapT tmp{{"Hello", "World"}};
+    check_references(tmp, tmp, tmp, tmp, StringMapT{tmp}, StringMapT{tmp},
+                     &tmp);
   }
 
   return 0;