Only exclude const-qualified char pointers.

String literals cannot be used to initialize *non-const* fields - such
usage would trigger the following warning: ISO C++11 does not allow
conversion from string literal to 'char *' [-Wwritable-strings].

Because of the above, this CL ensures makes a change to include in the
rewrite the fields below:
      char* char_ptr;
      wchar_t* wide_char_ptr;
while continuing to exclude the fields below:
      const char* const_char_ptr;
      const wchar_t* const_wide_char_ptr;

Bug: 1069567
Change-Id: Id660806c9e947220644b1ad10b083eeebaae36e8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2283771
Commit-Queue: Łukasz Anforowicz <lukasza@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Bartek Nowierski <bartekn@chromium.org>
Cr-Commit-Position: refs/heads/master@{#786549}

tools/clang/rewrite_raw_ptr_fields/RewriteRawPtrFields.cpp

@@ -988,9 +988,10 @@ int main(int argc, const char* argv[]) {
   // See the doc comment for the anyCharType matcher
   // and the testcases in tests/gen-char-test.cc.
   auto char_ptr_field_decl_matcher = fieldDecl(allOf(
-      field_decl_matcher, hasType(pointerType(pointee(
-                              hasUnqualifiedDesugaredType(anyCharType()))))));
-  FilteredExprWriter char_ptr_field_decl_writer(&output_helper, "char");
+      field_decl_matcher,
+      hasType(pointerType(pointee(qualType(allOf(
+          isConstQualified(), hasUnqualifiedDesugaredType(anyCharType()))))))));
+  FilteredExprWriter char_ptr_field_decl_writer(&output_helper, "const-char");
   match_finder.addMatcher(char_ptr_field_decl_matcher,
                           &char_ptr_field_decl_writer);
 

tools/clang/rewrite_raw_ptr_fields/tests/gen-char-expected.txt

 ==== BEGIN EDITS ====
 include-user-header:::gen-char-actual.cc:::-1:::-1:::base/memory/checked_ptr.h
-r:::gen-char-actual.cc:::1343:::6:::CheckedPtr<char> 
-r:::gen-char-actual.cc:::1361:::12:::CheckedPtr<const char> 
-r:::gen-char-actual.cc:::1391:::9:::CheckedPtr<wchar_t> 
-r:::gen-char-actual.cc:::1417:::15:::CheckedPtr<const wchar_t> 
+r:::gen-char-actual.cc:::1478:::12:::CheckedPtr<const char> 
+r:::gen-char-actual.cc:::1508:::15:::CheckedPtr<const wchar_t> 
+r:::gen-char-actual.cc:::1995:::6:::CheckedPtr<char> 
+r:::gen-char-actual.cc:::2013:::9:::CheckedPtr<wchar_t> 
 ==== END EDITS ====
 ==== BEGIN FIELD FILTERS ====
-MyStruct::char_ptr  # char
-MyStruct::const_char_ptr  # char
-MyStruct::const_wide_char_ptr  # char
-MyStruct::wide_char_ptr  # char
+MyStruct::const_char_ptr  # const-char
+MyStruct::const_wide_char_ptr  # const-char
 ==== END FIELD FILTERS ====

tools/clang/rewrite_raw_ptr_fields/tests/gen-char-test.cc

@@ -15,8 +15,9 @@
 struct MyStruct {
   // Chromium is built with a warning/error that there are no user-defined
   // constructors invoked when initializing global-scoped values.
-  // CheckedPtr<char> conversion might trigger a global constructor for string
-  // literals:
+  // CheckedPtr<char> conversion might trigger a global constructor call when a
+  // pointer field is initialized with a non-null value.  This frequently
+  // happens when initializing |const char*| fields with a string literal:
   //     struct MyStruct {
   //       int foo;
   //       CheckedPtr<const char> bar;
@@ -26,8 +27,16 @@ struct MyStruct {
   // Because of the above, we have a heuristic for all fields that point to a
   // char-like type - the heuristic causes such fields to be emitted as
   // candidates for the --field-filter-file.
-  char* char_ptr;
   const char* const_char_ptr;
-  wchar_t* wide_char_ptr;
   const wchar_t* const_wide_char_ptr;
+
+  // String literals cannot be used to initialize non-const fields - such usage
+  // would trigger the following warning: ISO C++11 does not allow conversion
+  // from string literal to 'char *' [-Wwritable-strings].
+  //
+  // Because of the above, we want to exclude non-const char pointers from the
+  // heuristic that excludes such fields from the rewrite.  Avoiding the
+  // double-negative: we want to include the fields below in the rewrite.
+  char* char_ptr;
+  wchar_t* wide_char_ptr;
 };