Modernize DeclTest

[hlopko]

Summary

This patch removes a call to the old ASTUnit::findFileRegionDecls and
replaces it with ast matchers.

[hlopko]

Rebase

clang/unittests/AST/DeclTest.cpp

 //===- unittests/AST/DeclTest.cpp --- Declaration tests -------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 // Unit tests for Decl nodes in the AST.
 //
 //===----------------------------------------------------------------------===//
 
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/Mangle.h"
 #include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/ASTMatchers/ASTMatchers.h"
 #include "clang/Basic/LLVM.h"
 #include "clang/Basic/TargetInfo.h"
 #include "clang/Tooling/Tooling.h"
 #include "llvm/IR/DataLayout.h"
 #include "gtest/gtest.h"
 
 using namespace clang::ast_matchers;
 using namespace clang::tooling;
StringRef Code = R"(
     };
   )";
   auto AST =
       tooling::buildASTFromCodeWithArgs(Code, {"-target", "i386-apple-darwin"});
   ASTContext &Ctx = AST->getASTContext();
   assert(Ctx.getTargetInfo().getDataLayout().getGlobalPrefix() &&
          "Expected target to have a global prefix");
   DiagnosticsEngine &Diags = AST->getDiagnostics();
-  SourceManager &SM = AST->getSourceManager();
-  FileID MainFileID = SM.getMainFileID();
 
-  // Find the method decls within the AST.
-  SmallVector<Decl *, 1> Decls;
-  AST->findFileRegionDecls(MainFileID, Code.find('{'), 0, Decls);
-  ASSERT_TRUE(Decls.size() == 1);
-  CXXRecordDecl *DeclS = cast<CXXRecordDecl>(Decls[0]);
+  auto *DeclS =
+      selectFirst<CXXRecordDecl>("d", match(cxxRecordDecl().bind("d"), Ctx));
   NamedDecl *DeclF = *DeclS->method_begin();
   NamedDecl *DeclG = *(++DeclS->method_begin());
 
   // Attach asm labels to the decls: one literal, and one not.
   DeclF->addAttr(::new (Ctx) AsmLabelAttr(Ctx, SourceLocation(), "foo",
                                           /*LiteralLabel=*/true));
   DeclG->addAttr(::new (Ctx) AsmLabelAttr(Ctx, SourceLocation(), "goo",
                                           /*LiteralLabel=*/false));