[lldb][Expression] Emit a 'Note' diagnostic that indicates the language used for expression evaluation

lldb/include/lldb/Target/Language.h

@@ -412,8 +412,15 @@ class Language : public PluginInterface {
   GetLanguageTypeFromString(const char *string) = delete;
   static lldb::LanguageType GetLanguageTypeFromString(llvm::StringRef string);
 
+  /// Returns the internal LLDB name for the specified language. When presenting
+  /// the language name to users, use \ref GetDisplayNameForLanguageType
+  /// instead.
   static const char *GetNameForLanguageType(lldb::LanguageType language);
 
+  /// Returns a user-friendly name for the specified language.
+  static llvm::StringRef
+  GetDisplayNameForLanguageType(lldb::LanguageType language);
+
   static void PrintAllLanguages(Stream &s, const char *prefix,
                                 const char *suffix);
 

lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionParser.cpp

@@ -74,6 +74,7 @@
 #include "lldb/Core/Debugger.h"
 #include "lldb/Core/Disassembler.h"
 #include "lldb/Core/Module.h"
+#include "lldb/Expression/DiagnosticManager.h"
 #include "lldb/Expression/IRExecutionUnit.h"
 #include "lldb/Expression/IRInterpreter.h"
 #include "lldb/Host/File.h"
@@ -96,6 +97,7 @@
 #include "Plugins/LanguageRuntime/ObjC/ObjCLanguageRuntime.h"
 #include "Plugins/Platform/MacOSX/PlatformDarwin.h"
 #include "lldb/Utility/XcodeSDK.h"
+#include "lldb/lldb-enumerations.h"
 
 #include <cctype>
 #include <memory>
@@ -570,7 +572,8 @@ static void SetupTargetOpts(CompilerInstance &compiler,
 
 static void SetupLangOpts(CompilerInstance &compiler,
                           ExecutionContextScope &exe_scope,
-                          const Expression &expr) {
+                          const Expression &expr,
+                          DiagnosticManager &diagnostic_manager) {
   Log *log = GetLog(LLDBLog::Expressions);
 
   // If the expression is being evaluated in the context of an existing stack
@@ -590,6 +593,9 @@ static void SetupLangOpts(CompilerInstance &compiler,
                      : lldb::eLanguageTypeUnknown),
         lldb_private::Language::GetNameForLanguageType(language));
 
+  lldb::LanguageType language_for_note = language;
+  std::string language_fallback_reason;
+
   LangOptions &lang_opts = compiler.getLangOpts();
 
   switch (language) {
@@ -603,13 +609,21 @@ static void SetupLangOpts(CompilerInstance &compiler,
     // family language, because the expression parser uses features of C++ to
     // capture values.
     lang_opts.CPlusPlus = true;
+
+    language_for_note = lldb::eLanguageTypeC_plus_plus;
+    language_fallback_reason =
+        "Expression evaluation in pure C not supported. ";
     break;
   case lldb::eLanguageTypeObjC:
     lang_opts.ObjC = true;
     // FIXME: the following language option is a temporary workaround,
     // to "ask for ObjC, get ObjC++" (see comment above).
     lang_opts.CPlusPlus = true;
 
+    language_for_note = lldb::eLanguageTypeObjC_plus_plus;
+    language_fallback_reason =
+        "Expression evaluation in pure Objective-C not supported. ";
+
     // Clang now sets as default C++14 as the default standard (with
     // GNU extensions), so we do the same here to avoid mismatches that
     // cause compiler error when evaluating expressions (e.g. nullptr not found
@@ -650,9 +664,27 @@ static void SetupLangOpts(CompilerInstance &compiler,
     lang_opts.CPlusPlus = true;
     lang_opts.CPlusPlus11 = true;
     compiler.getHeaderSearchOpts().UseLibcxx = true;
+
+    language_for_note = lldb::eLanguageTypeObjC_plus_plus;
+    if (language != language_for_note) {
+      if (language != lldb::eLanguageTypeUnknown)
+        language_fallback_reason = llvm::formatv(
+            "Expression evaluation in {0} not supported. ",
+            lldb_private::Language::GetDisplayNameForLanguageType(language));
+
+      language_fallback_reason +=
+          llvm::formatv("Falling back to default language. ");
+    }
     break;
   }
 
+  diagnostic_manager.AddDiagnostic(
+      llvm::formatv("{0}Ran expression as '{1}'.", language_fallback_reason,
+                    lldb_private::Language::GetDisplayNameForLanguageType(
+                        language_for_note))
+          .str(),
+      lldb::Severity::eSeverityInfo, DiagnosticOrigin::eDiagnosticOriginLLDB);
+
   lang_opts.Bool = true;
   lang_opts.WChar = true;
   lang_opts.Blocks = true;
@@ -736,8 +768,8 @@ static void SetupImportStdModuleLangOpts(CompilerInstance &compiler,
 
 ClangExpressionParser::ClangExpressionParser(
     ExecutionContextScope *exe_scope, Expression &expr,
-    bool generate_debug_info, std::vector<std::string> include_directories,
-    std::string filename)
+    bool generate_debug_info, DiagnosticManager &diagnostic_manager,
+    std::vector<std::string> include_directories, std::string filename)
     : ExpressionParser(exe_scope, expr, generate_debug_info), m_compiler(),
       m_pp_callbacks(nullptr),
       m_include_directories(std::move(include_directories)),
@@ -801,7 +833,7 @@ ClangExpressionParser::ClangExpressionParser(
   }
 
   // 4. Set language options.
-  SetupLangOpts(*m_compiler, *exe_scope, expr);
+  SetupLangOpts(*m_compiler, *exe_scope, expr, diagnostic_manager);
   auto *clang_expr = dyn_cast<ClangUserExpression>(&m_expr);
   if (clang_expr && clang_expr->DidImportCxxModules()) {
     LLDB_LOG(log, "Adding lang options for importing C++ modules");

lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionParser.h

@@ -65,6 +65,7 @@ class ClangExpressionParser : public ExpressionParser {
   ///     diagnostics (i.e. errors, warnings or notes from Clang).
   ClangExpressionParser(ExecutionContextScope *exe_scope, Expression &expr,
                         bool generate_debug_info,
+                        DiagnosticManager &diagnostic_manager,
                         std::vector<std::string> include_directories = {},
                         std::string filename = "<clang expression>");
 

lldb/source/Plugins/ExpressionParser/Clang/ClangFunctionCaller.cpp

@@ -189,8 +189,8 @@ ClangFunctionCaller::CompileFunction(lldb::ThreadSP thread_to_use_sp,
   lldb::ProcessSP jit_process_sp(m_jit_process_wp.lock());
   if (jit_process_sp) {
     const bool generate_debug_info = true;
-    auto *clang_parser = new ClangExpressionParser(jit_process_sp.get(), *this,
-                                                   generate_debug_info);
+    auto *clang_parser = new ClangExpressionParser(
+        jit_process_sp.get(), *this, generate_debug_info, diagnostic_manager);
     num_errors = clang_parser->Parse(diagnostic_manager);
     m_parser.reset(clang_parser);
   } else {

lldb/source/Plugins/ExpressionParser/Clang/ClangUserExpression.cpp

@@ -574,7 +574,7 @@ bool ClangUserExpression::TryParse(
 
   m_parser = std::make_unique<ClangExpressionParser>(
       exe_ctx.GetBestExecutionContextScope(), *this, generate_debug_info,
-      m_include_directories, m_filename);
+      diagnostic_manager, m_include_directories, m_filename);
 
   unsigned num_errors = m_parser->Parse(diagnostic_manager);
 
@@ -818,7 +818,7 @@ bool ClangUserExpression::Complete(ExecutionContext &exe_ctx,
   }
 
   ClangExpressionParser parser(exe_ctx.GetBestExecutionContextScope(), *this,
-                               false);
+                               false, diagnostic_manager);
 
   // We have to find the source code location where the user text is inside
   // the transformed expression code. When creating the transformed text, we

lldb/source/Plugins/ExpressionParser/Clang/ClangUtilityFunction.cpp

@@ -120,7 +120,7 @@ bool ClangUtilityFunction::Install(DiagnosticManager &diagnostic_manager,
 
   const bool generate_debug_info = true;
   ClangExpressionParser parser(exe_ctx.GetBestExecutionContextScope(), *this,
-                               generate_debug_info);
+                               generate_debug_info, diagnostic_manager);
 
   unsigned num_errors = parser.Parse(diagnostic_manager);
 

lldb/source/Target/Language.cpp

@@ -272,6 +272,10 @@ const char *Language::GetNameForLanguageType(LanguageType language) {
     return language_names[eLanguageTypeUnknown].name;
 }
 
+llvm::StringRef Language::GetDisplayNameForLanguageType(LanguageType language) {
+  return SourceLanguage(language).GetDescription();
+}
+
 void Language::PrintSupportedLanguagesForExpressions(Stream &s,
                                                      llvm::StringRef prefix,
                                                      llvm::StringRef suffix) {
@@ -544,9 +548,26 @@ Language::Language() = default;
 // Destructor
 Language::~Language() = default;
 
+static std::optional<llvm::dwarf::SourceLanguage>
+ToDwarfSourceLanguage(lldb::LanguageType language_type) {
+  if (language_type < lldb::eLanguageTypeLastStandardLanguage)
+    return static_cast<llvm::dwarf::SourceLanguage>(language_type);
+
+  switch (language_type) {
+  case eLanguageTypeMipsAssembler:
+    return llvm::dwarf::DW_LANG_Mips_Assembler;
+  default:
+    return std::nullopt;
+  }
+}
+
 SourceLanguage::SourceLanguage(lldb::LanguageType language_type) {
-  auto lname =
-      llvm::dwarf::toDW_LNAME((llvm::dwarf::SourceLanguage)language_type);
+  std::optional<llvm::dwarf::SourceLanguage> dwarf_lang =
+      ToDwarfSourceLanguage(language_type);
+  if (!dwarf_lang)
+    return;
+
+  auto lname = llvm::dwarf::toDW_LNAME(*dwarf_lang);
   if (!lname)
     return;
   name = lname->first;
@@ -561,11 +582,8 @@ lldb::LanguageType SourceLanguage::AsLanguageType() const {
 }
 
 llvm::StringRef SourceLanguage::GetDescription() const {
-  LanguageType type = AsLanguageType();
-  if (type)
-    return Language::GetNameForLanguageType(type);
   return llvm::dwarf::LanguageDescription(
-      (llvm::dwarf::SourceLanguageName)name);
+      static_cast<llvm::dwarf::SourceLanguageName>(name));
 }
 bool SourceLanguage::IsC() const { return name == llvm::dwarf::DW_LNAME_C; }
 

lldb/test/API/commands/expression/diagnostics/TestExprDiagnostics.py

@@ -215,8 +215,22 @@ def check_error(diags):
 
             details = diags.GetValueForKey("details")
 
-            # Detail 1/2: undeclared 'a'
+            # Detail 1/3: note: requested expression language
             diag = details.GetItemAtIndex(0)
+            self.assertEqual(str(diag.GetValueForKey("severity")), "note")
+            self.assertIn(
+                "Ran expression as 'C++", str(diag.GetValueForKey("message"))
+            )
+            self.assertIn(
+                "Ran expression as 'C++", str(diag.GetValueForKey("rendered"))
+            )
+            self.assertEqual(str(diag.GetValueForKey("source_location")), "")
+            self.assertEqual(str(diag.GetValueForKey("file")), "")
+            self.assertFalse(diag.GetValueForKey("hidden").GetBooleanValue())
+            self.assertFalse(diag.GetValueForKey("in_user_input").GetBooleanValue())
+
+            # Detail 2/3: undeclared 'a'
+            diag = details.GetItemAtIndex(1)
 
             severity = diag.GetValueForKey("severity")
             message = diag.GetValueForKey("message")
@@ -234,8 +248,8 @@ def check_error(diags):
             self.assertFalse(hidden.GetBooleanValue())
             self.assertTrue(in_user_input.GetBooleanValue())
 
-            # Detail 1/2: undeclared 'b'
-            diag = details.GetItemAtIndex(1)
+            # Detail 3/3: undeclared 'b'
+            diag = details.GetItemAtIndex(2)
             message = diag.GetValueForKey("message")
             self.assertIn("undeclared identifier 'b'", str(message))
 

lldb/test/API/python_api/interpreter/TestCommandInterpreterAPI.py

@@ -1,4 +1,4 @@
-"""Test the SBCommandInterpreter APIs."""
+"""tESt the SBCommandInterpreter APIs."""
 
 import json
 import lldb
@@ -156,13 +156,15 @@ def test_get_transcript(self):
         self.assertEqual(transcript[0]["error"], "")
 
         # (lldb) an-unknown-command
-        self.assertEqual(transcript[1],
+        self.assertEqual(
+            transcript[1],
             {
                 "command": "an-unknown-command",
                 # Unresolved commands don't have "commandName"/"commandArguments"
                 "output": "",
                 "error": "error: 'an-unknown-command' is not a valid command.\n",
-            })
+            },
+        )
 
         # (lldb) br s -f main.c -l <line>
         self.assertEqual(transcript[2]["command"], "br s -f main.c -l %d" % self.line)
@@ -175,14 +177,17 @@ def test_get_transcript(self):
         self.assertEqual(transcript[2]["error"], "")
 
         # (lldb) p a
-        self.assertEqual(transcript[3],
+        self.assertEqual(
+            transcript[3],
             {
                 "command": "p a",
                 "commandName": "dwim-print",
                 "commandArguments": "-- a",
                 "output": "",
-                "error": "error: <user expression 0>:1:1: use of undeclared identifier 'a'\n    1 | a\n      | ^\n",
-            })
+                "error": "note: Falling back to default language. Ran expression as 'Objective C++'.\n"
+                "error: <user expression 0>:1:1: use of undeclared identifier 'a'\n    1 | a\n      | ^\n",
+            },
+        )
 
         # (lldb) statistics dump
         self.assertEqual(transcript[4]["command"], "statistics dump")
@@ -203,7 +208,10 @@ def test_save_transcript_setting_default(self):
         self.assertTrue(ci, VALID_COMMAND_INTERPRETER)
 
         # The setting's default value should be "false"
-        self.runCmd("settings show interpreter.save-transcript", "interpreter.save-transcript (boolean) = false\n")
+        self.runCmd(
+            "settings show interpreter.save-transcript",
+            "interpreter.save-transcript (boolean) = false\n",
+        )
 
     def test_save_transcript_setting_off(self):
         ci = self.dbg.GetCommandInterpreter()
@@ -250,17 +258,37 @@ def test_get_transcript_returns_copy(self):
         structured_data_1 = ci.GetTranscript()
         self.assertTrue(structured_data_1.IsValid())
         self.assertEqual(structured_data_1.GetSize(), 1)
-        self.assertEqual(structured_data_1.GetItemAtIndex(0).GetValueForKey("command").GetStringValue(100), "version")
+        self.assertEqual(
+            structured_data_1.GetItemAtIndex(0)
+            .GetValueForKey("command")
+            .GetStringValue(100),
+            "version",
+        )
 
         # Run some more commands and get the transcript as structured data again
         self.runCmd("help")
         structured_data_2 = ci.GetTranscript()
         self.assertTrue(structured_data_2.IsValid())
         self.assertEqual(structured_data_2.GetSize(), 2)
-        self.assertEqual(structured_data_2.GetItemAtIndex(0).GetValueForKey("command").GetStringValue(100), "version")
-        self.assertEqual(structured_data_2.GetItemAtIndex(1).GetValueForKey("command").GetStringValue(100), "help")
+        self.assertEqual(
+            structured_data_2.GetItemAtIndex(0)
+            .GetValueForKey("command")
+            .GetStringValue(100),
+            "version",
+        )
+        self.assertEqual(
+            structured_data_2.GetItemAtIndex(1)
+            .GetValueForKey("command")
+            .GetStringValue(100),
+            "help",
+        )
 
         # Now, the first structured data should remain unchanged
         self.assertTrue(structured_data_1.IsValid())
         self.assertEqual(structured_data_1.GetSize(), 1)
-        self.assertEqual(structured_data_1.GetItemAtIndex(0).GetValueForKey("command").GetStringValue(100), "version")
+        self.assertEqual(
+            structured_data_1.GetItemAtIndex(0)
+            .GetValueForKey("command")
+            .GetStringValue(100),
+            "version",
+        )