Emit constexpr-initialized fields as candidates for exclusion.

After this CL, the rewriter will detect fields that are initialized
with non-nullptr value in constexpr constructors.  Such fields will
be emitted as candidates for exclusion via --exclude-fields cmdline
parameter.

This CL should help ensure that the build is successful, once we
stop excluding |const char* fields| from the rewrite.  In particular,
performance_manager::PriorityAndReason::reason_ field needs to be
excluded in practice.  Additionally, this CL should help to automate
excluding of the various base::FeatureParam fields/scenarios (they
are currently covered via manual-fields-to-ignore.txt).

Bug: 1069567
Change-Id: I122a329577f77d8172e26f189b5155af742a33c2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2495719
Auto-Submit: Łukasz Anforowicz <lukasza@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#820840}

tools/clang/rewrite_raw_ptr_fields/RewriteRawPtrFields.cpp

@@ -1050,6 +1050,18 @@ int main(int argc, const char* argv[]) {
   match_finder.addMatcher(overlapping_field_decl_matcher,
                           &overlapping_field_decl_writer);
 
+  // Matches fields initialized with a non-nullptr value in a constexpr
+  // constructor.  See also the testcase in tests/gen-constexpr-ctor-test.cc.
+  auto constexpr_ctor_initialized_field_matcher = cxxConstructorDecl(allOf(
+      isConstexpr(),
+      forEachConstructorInitializer(allOf(
+          forField(field_decl_matcher), withInitializer(unless(ignoringImplicit(
+                                            cxxNullPtrLiteralExpr())))))));
+  FilteredExprWriter constexpr_ctor_initialized_field_writer(
+      &output_helper, "constexpr-ctor-initializer");
+  match_finder.addMatcher(constexpr_ctor_initialized_field_matcher,
+                          &constexpr_ctor_initialized_field_writer);
+
   // See the doc comment for the isInMacroLocation matcher
   // and the testcases in tests/gen-macro-test.cc.
   auto macro_field_decl_matcher =

tools/clang/rewrite_raw_ptr_fields/tests/gen-constexpr-ctor-expected.txt

+==== BEGIN EDITS ====
+include-user-header:::/usr/local/google/home/lukasza/src/chromium4/src/tools/clang/rewrite_raw_ptr_fields/tests/gen-constexpr-ctor-actual.cc:::-1:::-1:::base/memory/checked_ptr.h
+r:::/usr/local/google/home/lukasza/src/chromium4/src/tools/clang/rewrite_raw_ptr_fields/tests/gen-constexpr-ctor-actual.cc:::1045:::5:::CheckedPtr<int> 
+r:::/usr/local/google/home/lukasza/src/chromium4/src/tools/clang/rewrite_raw_ptr_fields/tests/gen-constexpr-ctor-actual.cc:::1153:::5:::CheckedPtr<int> 
+r:::/usr/local/google/home/lukasza/src/chromium4/src/tools/clang/rewrite_raw_ptr_fields/tests/gen-constexpr-ctor-actual.cc:::1271:::5:::CheckedPtr<int> 
+==== END EDITS ====
+==== BEGIN FIELD FILTERS ====
+Foo::ptr2_  # constexpr-ctor-initializer
+Foo::ptr_  # constexpr-ctor-initializer
+==== END FIELD FILTERS ====

tools/clang/rewrite_raw_ptr_fields/tests/gen-constexpr-ctor-test.cc

+// Copyright 2020 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// This file (and other gen-*-test.cc files) tests generation of output for
+// --field-filter-file and therefore the expectations file
+// (gen-char-expected.txt) needs to be compared against the raw output of the
+// rewriter (rather than against the actual edits result).  This makes the test
+// incompatible with other tests, which require passing --apply-edits switch to
+// test_tool.py and so to disable the test it is named *-test.cc rather than
+// *-original.cc.
+//
+// To run the test use tools/clang/rewrite_raw_ptr_fields/tests/run_all_tests.py
+
+class Foo {
+ public:
+  constexpr explicit Foo(int* ptr) : ptr_(ptr), ptr2_(ptr), null_(nullptr) {}
+
+ private:
+  // CheckedPtr(T*) constructor is non-constexpr and therefore CheckedPtr fields
+  // cannot be initialized in constexpr constructors - such fields should be
+  // emitted as candidates for the --field-filter-file.
+  int* ptr_;
+
+  // Testing that all initializers and fields are covered (i.e. not just the
+  // first one).
+  int* ptr2_;
+
+  // CheckedPtr(nullptr_t) is constexpr and therefore the field below doesn't
+  // need to be skipped.
+  int* null_;
+};