LSC: C++ DebugString to AbslStringify

In this LSC, we replace calls to C++ Protobuf DebugString APIs with implicit AbslStringify conversions or absl::StrCat. This makes debug information incompatible with TextFormat parsers (go/explicit-debug-string), redacts Datapol-annotated SPII values (go/redact-debug-string), and introduces per-process-randomized syntax.

Background:
DebugString callers should not rely on DebugString output (go/no-more-debugstring). proto2::Message DebugString APIs will be deprecated by Protobuf's AbslStringify in order to support SPII redaction. We are incrementally migrating DebugString calls to the new API whenever we are confident it is safe to do so. If this CL causes breakage, please roll back and notify us (orrery-debug-string@).

LSC proposal: go/cpp-debug-string-to-absl-stringify
ISE LSC checklist: go/cpp-debugstring-to-stringify-checklist

Tested:
    TAP --sample ran all affected tests and none failed
    http://test/OCL:598320114:BASE:598306044:1705216156011:87332a0f
PiperOrigin-RevId: 598836189

clif/backend/BUILD

@@ -62,6 +62,7 @@ cc_library(
         "//clif/protos:ast_cc_proto",
         "@com_google_absl//absl/container:btree",
         "@com_google_absl//absl/log",
+        "@com_google_absl//absl/strings",
         "@com_google_googletest//:gtest_prod",
         "@llvm-project//clang:ast",
         "@llvm-project//clang:sema",

clif/backend/code_builder.cc

@@ -79,6 +79,7 @@
 #include <unordered_map>
 #include <vector>
 
+#include "absl/strings/str_cat.h"
 #include "clif/backend/strutil.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
@@ -390,7 +391,7 @@ const std::string& CodeBuilder::BuildCode(
     current_line_.pop_back();
     current_file_.pop_back();
   }
-  LLVM_DEBUG(llvm::dbgs() << clif_ast->DebugString());
+  LLVM_DEBUG(llvm::dbgs() << absl::StrCat(*clif_ast));
   LLVM_DEBUG(llvm::dbgs() << code_);
   return code_;
 }

clif/backend/matcher.cc

@@ -28,6 +28,7 @@
 
 #include "absl/container/btree_map.h"
 #include "absl/log/log.h"
+#include "absl/strings/str_cat.h"
 #include "clif/backend/strutil.h"
 #include "clang/AST/Expr.h"
 #include "clang/AST/Mangle.h"
@@ -351,7 +352,7 @@ bool ClifMatcher::CompileMatchAndSet(
     const std::string& input_file_name,
     const AST& clif_ast,
     AST* modified_clif_ast) {
-  LLVM_DEBUG(llvm::dbgs() << clif_ast.DebugString());
+  LLVM_DEBUG(llvm::dbgs() << absl::StrCat(clif_ast));
   *modified_clif_ast = clif_ast;
   modified_clif_ast->set_clif_matcher_argv0(clif_matcher_argv0_);
   modified_clif_ast->set_clif_matcher_version_stamp(kMatcherVersionStamp);
@@ -406,7 +407,7 @@ std::string ClifMatcher::GetQualTypeClifName(QualType qual_type) const {
 bool ClifMatcher::MatchAndSetAST(AST* clif_ast) {
   assert(ast_ != nullptr && "RunCompiler must be called prior to this.");
   int num_unmatched = MatchAndSetDecls(clif_ast->mutable_decls());
-  LLVM_DEBUG(llvm::dbgs() << "Matched proto:\n" << clif_ast->DebugString());
+  LLVM_DEBUG(llvm::dbgs() << "Matched proto:\n" << absl::StrCat(*clif_ast));
   return num_unmatched == 0;
 }
 
@@ -1172,7 +1173,7 @@ bool ClifMatcher::MatchAndSetEnum(EnumDecl* enum_decl) {
       clif_name->set_native(result.GetFirst()->getNameAsString());
     }
   }
-  LLVM_DEBUG(llvm::dbgs() << enum_decl->DebugString());
+  LLVM_DEBUG(llvm::dbgs() << absl::StrCat(*enum_decl));
   return true;
 }