[LLDB] Fix type formatting empty c-strings (#68924)

The type formatter code is effectively considering empty strings as read
errors, which is wrong. The fix is very simple. We should rely on the
error object and stop checking the size. I also added a test.

Author: walter-erquinigo

lldb/source/DataFormatters/TypeFormat.cpp

@@ -81,9 +81,9 @@ bool TypeFormatImpl_Format::FormatObject(ValueObject *valobj,
               WritableDataBufferSP buffer_sp(
                   new DataBufferHeap(max_len + 1, 0));
               Address address(valobj->GetPointerValue());
-              if (target_sp->ReadCStringFromMemory(
-                      address, (char *)buffer_sp->GetBytes(), max_len, error) &&
-                  error.Success())
+              target_sp->ReadCStringFromMemory(
+                  address, (char *)buffer_sp->GetBytes(), max_len, error);
+              if (error.Success())
                 data.SetData(buffer_sp);
             }
           }

lldb/test/API/functionalities/data-formatter/builtin-formats/TestBuiltinFormats.py

@@ -3,9 +3,9 @@
 """
 
 import lldb
+from lldbsuite.test import lldbutil
 from lldbsuite.test.decorators import *
 from lldbsuite.test.lldbtest import *
-from lldbsuite.test import lldbutil
 
 
 class TestCase(TestBase):
@@ -19,6 +19,20 @@ def getFormatted(self, format, expr):
         self.assertTrue(result.Succeeded(), result.GetError())
         return result.GetOutput()
 
+    @no_debug_info_test
+    @skipIfWindows
+    def testAllPlatforms(self):
+        self.build()
+        lldbutil.run_to_source_breakpoint(
+            self, "// break here", lldb.SBFileSpec("main.cpp")
+        )
+        # We can dump correctly non char* c-strings with explicit formatting.
+        self.assertIn(' = ""', self.getFormatted("c-string", "void_empty_cstring"))
+        self.assertIn(' = ""', self.getFormatted("c-string", "empty_cstring"))
+
+    # TODO: Move as many asserts as possible within this function to `testAllPlatforms`.
+    # Currently `arm` is being skipped even though many asserts would effectively
+    # pass.
     @no_debug_info_test
     @skipIfWindows
     # uint128_t not available on arm.

lldb/test/API/functionalities/data-formatter/builtin-formats/main.cpp

@@ -1,8 +1,10 @@
 #include <cstdint>
 
 const char cstring[15] = " \033\a\b\f\n\r\t\vaA09\0";
+const char *empty_cstring = "";
 
 int main() {
   int use = *cstring;
+  void *void_empty_cstring = (void *)empty_cstring;
   return use; // break here
 }