[NFC] Minimize header includes (llvm#66339)

Minimize the headers included in header files to reduce the number of
files that need recompiled after a change.

Author: bwendling

clang/include/clang/Basic/AttrSubjectMatchRules.h

@@ -9,10 +9,12 @@
 #ifndef LLVM_CLANG_BASIC_ATTRSUBJECTMATCHRULES_H
 #define LLVM_CLANG_BASIC_ATTRSUBJECTMATCHRULES_H
 
-#include "clang/Basic/SourceLocation.h"
 #include "llvm/ADT/DenseMap.h"
 
 namespace clang {
+
+class SourceRange;
+
 namespace attr {
 
 /// A list of all the recognized kinds of attributes.

clang/include/clang/Basic/AttributeCommonInfo.h

@@ -13,12 +13,14 @@
 
 #ifndef LLVM_CLANG_BASIC_ATTRIBUTECOMMONINFO_H
 #define LLVM_CLANG_BASIC_ATTRIBUTECOMMONINFO_H
+
 #include "clang/Basic/SourceLocation.h"
 #include "clang/Basic/TokenKinds.h"
 
 namespace clang {
-class IdentifierInfo;
+
 class ASTRecordWriter;
+class IdentifierInfo;
 
 class AttributeCommonInfo {
 public:

clang/include/clang/Basic/Attributes.h

@@ -10,12 +10,12 @@
 #define LLVM_CLANG_BASIC_ATTRIBUTES_H
 
 #include "clang/Basic/AttributeCommonInfo.h"
-#include "clang/Basic/LangOptions.h"
-#include "clang/Basic/TargetInfo.h"
 
 namespace clang {
 
 class IdentifierInfo;
+class LangOptions;
+class TargetInfo;
 
 /// Return the version number associated with the attribute if we
 /// recognize and implement the attribute specified by the given information.

clang/lib/Basic/Attributes.cpp

@@ -1,8 +1,22 @@
+//===--- Attributes.cpp ---------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the AttributeCommonInfo interface.
+//
+//===----------------------------------------------------------------------===//
+
 #include "clang/Basic/Attributes.h"
 #include "clang/Basic/AttrSubjectMatchRules.h"
-#include "clang/Basic/AttributeCommonInfo.h"
 #include "clang/Basic/IdentifierTable.h"
+#include "clang/Basic/LangOptions.h"
 #include "clang/Basic/ParsedAttrInfo.h"
+#include "clang/Basic/TargetInfo.h"
+
 using namespace clang;
 
 static int hasAttributeImpl(AttributeCommonInfo::Syntax Syntax, StringRef Name,

clang/lib/Basic/IdentifierTable.cpp

@@ -25,7 +25,6 @@
 #include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/Allocator.h"
-#include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/raw_ostream.h"
 #include <cassert>
 #include <cstdio>
@@ -52,8 +51,7 @@ namespace {
 
 /// A simple identifier lookup iterator that represents an
 /// empty sequence of identifiers.
-class EmptyLookupIterator : public IdentifierIterator
-{
+class EmptyLookupIterator : public IdentifierIterator {
 public:
   StringRef Next() override { return StringRef(); }
 };

clang/lib/Parse/ParseStmt.cpp

@@ -14,6 +14,7 @@
 #include "clang/AST/PrettyDeclStackTrace.h"
 #include "clang/Basic/Attributes.h"
 #include "clang/Basic/PrettyStackTrace.h"
+#include "clang/Basic/TargetInfo.h"
 #include "clang/Basic/TokenKinds.h"
 #include "clang/Parse/LoopHint.h"
 #include "clang/Parse/Parser.h"