swift-module-digester: refactor the ABI/API diagnostics to use DiagnosticEngine. NFC (#18957)

Before this patch, we used to define tooling-specific diagnostics. With adding more
checking logics, we found this mechanism hard to extend. This patch
eliminates the home-made diagnostics model to use the one from compiler, which provides
several benefits: less boiler-templates, better integration with DiagnosticConsumer,
and easy ordering of detected issues.

tools/swift-api-digester/ModuleDiagsConsumer.cpp

@@ -0,0 +1,94 @@
+//===--- ModuleDiagsConsumer.cpp - Print module differ diagnostics --*- C++ -*-===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+//
+//  This file implements the ModuleDifferDiagsConsumer class, which displays
+//  diagnostics from the module differ as text to an output.
+//
+//===----------------------------------------------------------------------===//
+
+#include "swift/AST/DiagnosticEngine.h"
+#include "swift/AST/DiagnosticsModuleDiffer.h"
+#include "ModuleDiagsConsumer.h"
+
+using namespace swift;
+
+namespace {
+// Reproduce the DiagIDs, as we want both the size and access to the raw ids
+// themselves.
+enum LocalDiagID : uint32_t {
+#define DIAG(KIND, ID, Options, Text, Signature) ID,
+#include "swift/AST/DiagnosticsAll.def"
+  NumDiags
+};
+
+static StringRef getCategoryName(uint32_t ID) {
+  switch(ID) {
+  case LocalDiagID::removed_decl:
+    return "/* Removed Decls */";
+  case LocalDiagID::moved_decl:
+    return "/* Moved Decls */";
+  case LocalDiagID::renamed_decl:
+    return "/* Renamed Decls */";
+  case LocalDiagID::decl_attr_change:
+  case LocalDiagID::decl_new_attr:
+    return "/* Decl Attribute changes */";
+  case LocalDiagID::decl_type_change:
+    return "/* Type Changes */";
+  case LocalDiagID::raw_type_change:
+    return "/* RawRepresentable Changes */";
+  case LocalDiagID::generic_sig_change:
+    return "/* Generic Signature Changes */";
+  default:
+    return StringRef();
+  }
+}
+}
+
+swift::ide::api::
+ModuleDifferDiagsConsumer::ModuleDifferDiagsConsumer():
+    PrintingDiagnosticConsumer(llvm::errs()) {
+#define DIAG(KIND, ID, Options, Text, Signature)                              \
+  auto ID = getCategoryName(LocalDiagID::ID);                                 \
+  assert(!ID.empty());                                                        \
+  AllDiags[ID] = std::set<std::string>();
+#include "swift/AST/DiagnosticsModuleDiffer.def"
+}
+
+void swift::ide::api::
+ModuleDifferDiagsConsumer::handleDiagnostic(SourceManager &SM, SourceLoc Loc,
+                        DiagnosticKind Kind,
+                        StringRef FormatString,
+                        ArrayRef<DiagnosticArgument> FormatArgs,
+                        const DiagnosticInfo &Info) {
+  auto Category = getCategoryName((uint32_t)Info.ID);
+  if (Category.empty()) {
+    PrintingDiagnosticConsumer::handleDiagnostic(SM, Loc, Kind, FormatString,
+      FormatArgs, Info);
+    return;
+  }
+  llvm::SmallString<256> Text;
+  {
+    llvm::raw_svector_ostream Out(Text);
+    DiagnosticEngine::formatDiagnosticText(Out, FormatString, FormatArgs);
+  }
+  AllDiags[Category].insert(Text.str().str());
+}
+
+swift::ide::api::ModuleDifferDiagsConsumer::~ModuleDifferDiagsConsumer() {
+  for (auto &Pair: AllDiags) {
+    llvm::outs() << "\n";
+    llvm::outs() << Pair.first << "\n";
+    for (auto &Item: Pair.second) {
+      llvm::outs() << Item << "\n";
+    }
+  }
+}