[lldb] Don't emit a warning when using Objective-C getters in expressions

[teemperor]

Summary

Clang emits a warning when accessing an Objective-C getter but not using the result.
This gets triggered when just trying to print a getter value in the expression parser (where
Clang just sees a normal expression like obj.getter while parsing).

This patch just disables the warning in the expression parser (similar to what we do with
the C++ equivalent of just accessing a member variable but not doing anything with it).

[kastiglione]

lldb/test/API/lang/objc/warnings-in-expr-parser/main.m

3–10

property getters and setters are automatically generated, this could be an empty @implementation.

15

I don't think the pool is necessary, the MyClass instance isn't using it.

You could compile this file with -fobjc-arc and then it would do automatic memory management, tho for this file it really doesn't matter.

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

 }
 
 /// Configures Clang diagnostics for the expression parser.
 static void SetupDefaultClangDiagnostics(CompilerInstance &compiler) {
   // List of Clang warning groups that are not useful when parsing expressions.
   const std::vector<const char *> groupsToIgnore = {
       "unused-value",
       "odr",
+      "unused-getter-return-value",
   };
   for (const char *group : groupsToIgnore) {
     compiler.getDiagnostics().setSeverityForGroup(
         clang::diag::Flavor::WarningOrError, group,
         clang::diag::Severity::Ignored, SourceLocation());
   }
 }
 

lldb/test/API/lang/objc/warnings-in-expr-parser/Makefile

+OBJC_SOURCES := main.m
+LD_EXTRAS := -framework Foundation
+
+include Makefile.rules

lldb/test/API/lang/objc/warnings-in-expr-parser/TestObjCWarningsInExprParser.py

+"""
+Test the warnings that LLDB emits when parsing Objective-C expressions.
+"""
+
+import lldb
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+
+class TestCase(TestBase):
+
+    mydir = TestBase.compute_mydir(__file__)
+
+    @skipUnlessDarwin
+    @no_debug_info_test
+    def test(self):
+        self.build()
+        lldbutil.run_to_source_breakpoint(self, "// break here", lldb.SBFileSpec("main.m"))
+
+        # Don't warn about not using the result of getters. This is perfectly
+        # fine in the expression parser and LLDB shouldn't warn the user about that.
+        result = self.frame().EvaluateExpression("m.m; unknown_var_to_cause_an_error")
+        self.assertNotIn("getters should not be used for side effects", str(result.GetError()))

lldb/test/API/lang/objc/warnings-in-expr-parser/main.m

+#include <Foundation/Foundation.h>
+
+@interface MyClass : NSObject
+@property(getter=getM) int m;
+@end
+
+@implementation MyClass {
+}
+- (int)getM {
+  return 1;
+}
+@end
+
+int main() {
+  NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
+  MyClass *m = [[MyClass alloc] init];
+  m.m; // break here
+  [pool drain];
+  return 0; // break here
+}