1 files changed, 119 insertions, 0 deletions
diff --git a/clang/lib/Tooling/Inclusions/HeaderAnalysis.cpp b/clang/lib/Tooling/Inclusions/HeaderAnalysis.cpp
new file mode 100644
index 000000000000..49d23908d33b
--- /dev/null
+++ b/clang/lib/Tooling/Inclusions/HeaderAnalysis.cpp
@@ -0,0 +1,119 @@
+//===--- HeaderAnalysis.cpp -------------------------------------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "clang/Tooling/Inclusions/HeaderAnalysis.h"
+#include "clang/Basic/SourceLocation.h"
+#include "clang/Lex/HeaderSearch.h"
+
+namespace clang::tooling {
+namespace {
+
+// Is Line an #if or #ifdef directive?
+// FIXME: This makes headers with #ifdef LINUX/WINDOWS/MACOS marked as non
+// self-contained and is probably not what we want.
+bool isIf(llvm::StringRef Line) {
+  Line = Line.ltrim();
+  if (!Line.consume_front("#"))
+    return false;
+  Line = Line.ltrim();
+  return Line.startswith("if");
+}
+
+// Is Line an #error directive mentioning includes?
+bool isErrorAboutInclude(llvm::StringRef Line) {
+  Line = Line.ltrim();
+  if (!Line.consume_front("#"))
+    return false;
+  Line = Line.ltrim();
+  if (!Line.startswith("error"))
+    return false;
+  return Line.contains_insensitive(
+      "includ"); // Matches "include" or "including".
+}
+
+// Heuristically headers that only want to be included via an umbrella.
+bool isDontIncludeMeHeader(StringRef Content) {
+  llvm::StringRef Line;
+  // Only sniff up to 100 lines or 10KB.
+  Content = Content.take_front(100 * 100);
+  for (unsigned I = 0; I < 100 && !Content.empty(); ++I) {
+    std::tie(Line, Content) = Content.split('\n');
+    if (isIf(Line) && isErrorAboutInclude(Content.split('\n').first))
+      return true;
+  }
+  return false;
+}
+
+bool isImportLine(llvm::StringRef Line) {
+  Line = Line.ltrim();
+  if (!Line.consume_front("#"))
+    return false;
+  Line = Line.ltrim();
+  return Line.startswith("import");
+}
+
+llvm::StringRef getFileContents(const FileEntry *FE, const SourceManager &SM) {
+  return const_cast<SourceManager &>(SM)
+      .getMemoryBufferForFileOrNone(FE)
+      .value_or(llvm::MemoryBufferRef())
+      .getBuffer();
+}
+
+} // namespace
+
+bool isSelfContainedHeader(const FileEntry *FE, const SourceManager &SM,
+                           HeaderSearch &HeaderInfo) {
+  assert(FE);
+  if (!HeaderInfo.isFileMultipleIncludeGuarded(FE) &&
+      !HeaderInfo.hasFileBeenImported(FE) &&
+      // Any header that contains #imports is supposed to be #import'd so no
+      // need to check for anything but the main-file.
+      (SM.getFileEntryForID(SM.getMainFileID()) != FE ||
+       !codeContainsImports(getFileContents(FE, SM))))
+    return false;
+  // This pattern indicates that a header can't be used without
+  // particular preprocessor state, usually set up by another header.
+  return !isDontIncludeMeHeader(getFileContents(FE, SM));
+}
+
+bool codeContainsImports(llvm::StringRef Code) {
+  // Only sniff up to 100 lines or 10KB.
+  Code = Code.take_front(100 * 100);
+  llvm::StringRef Line;
+  for (unsigned I = 0; I < 100 && !Code.empty(); ++I) {
+    std::tie(Line, Code) = Code.split('\n');
+    if (isImportLine(Line))
+      return true;
+  }
+  return false;
+}
+
+std::optional<StringRef> parseIWYUPragma(const char *Text) {
+  // Skip the comment start, // or /*.
+  if (Text[0] != '/' || (Text[1] != '/' && Text[1] != '*'))
+    return std::nullopt;
+  bool BlockComment = Text[1] == '*';
+  Text += 2;
+
+  // Per spec, direcitves are whitespace- and case-sensitive.
+  constexpr llvm::StringLiteral IWYUPragma = " IWYU pragma: ";
+  if (strncmp(Text, IWYUPragma.data(), IWYUPragma.size()))
+    return std::nullopt;
+  Text += IWYUPragma.size();
+  const char *End = Text;
+  while (*End != 0 && *End != '\n')
+    ++End;
+  StringRef Rest(Text, End - Text);
+  // Strip off whitespace and comment markers to avoid confusion. This isn't
+  // fully-compatible with IWYU, which splits into whitespace-delimited tokens.
+  if (BlockComment)
+    Rest.consume_back("*/");
+  return Rest.trim();
+}
+
+} // namespace clang::tooling