[include-fixer] Improve include paths' minimization.

[hokein]

Summary

The file path of a symbol in yaml database is an absolute
file path. However, HeaderSearch::suggestPathToFileForDiagnostics assumes that
the FileEntry::Name is a relative file path based on header search path,
otherwise, it returns an absolute file path.

This patch makes include-fixer follow this assumption, so that
include-fixer can get the most appropriate header path.

[hokein]

Minor update.

[hokein]

Update.

[bkramer]

Making one path relative to another part is a hard problem. We'd need to make this work on windows and possibly also have it working in presence of symlinks. I'd much prefer to make paths in the YAML file relative to the "directory" in the compilation database, which is always the working directory of any clang tool. Would that break something?

[hokein]

Abandon this, in favor of http://reviews.llvm.org/D20158.

include-fixer/IncludeFixer.cpp

 #define DEBUG_TYPE "include-fixer"
 
 using namespace clang;
 
 namespace clang {
 namespace include_fixer {
 namespace {
 
+// Returns a relative filepath to FilePath from Dir.
+// For example:
+//   RelativePath("/foo/bar", "/foo") => "bar"
+//   RelativePath("/foo/bar/test", "foo/bar/include") => "../test"
+std::string RelativePath(StringRef FilePath, StringRef Dir) {
+  SmallString<256> Result;
+  SmallVector<StringRef, 5> FilePathComponents;
+  SmallVector<StringRef, 5> DirComponents;
+  FilePath.split(FilePathComponents, '/');
+  Dir.split(DirComponents, '/');
+
+  for (size_t FI = 0, DI = 0, FE = FilePathComponents.size(),
+              DE = DirComponents.size();
+       FI < FE && DI < DE; ++FI, ++DI) {
+    if (FilePathComponents[FI] != DirComponents[DI]) {
+      for (size_t Count = DE - DI; Count > 0; --Count)
+        llvm::sys::path::append(Result, "..");
+      for (; FI < FE; ++FI)
+        llvm::sys::path::append(Result, FilePathComponents[FI]);
+      break;
+    }
+  }
+  return Result.str();
+}
+
 class Action;
 
 class PreprocessorHooks : public clang::PPCallbacks {
 public:
   explicit PreprocessorHooks(Action *EnclosingPass)
       : EnclosingPass(EnclosingPass), TrackedFile(nullptr) {}
 
   void FileChanged(clang::SourceLocation loc,
public:
   std::string minimizeInclude(StringRef Include,
                               clang::SourceManager &SourceManager,
                               clang::HeaderSearch &HeaderSearch) {
     if (!MinimizeIncludePaths)
       return Include;
 
     // Get the FileEntry for the include.
     StringRef StrippedInclude = Include.trim("\"<>");
+
+    auto BuildDir = SourceManager.getFileManager()
+                          .getVirtualFileSystem()
+                          ->getCurrentWorkingDirectory();
+    if (!BuildDir)
+      return Include;
+    StringRef PathRelativeToBuildDir = RelativePath(StrippedInclude, *BuildDir);
+
     const FileEntry *Entry =
-        SourceManager.getFileManager().getFile(StrippedInclude);
+        SourceManager.getFileManager().getFile(PathRelativeToBuildDir);
 
     // If the file doesn't exist return the path from the database.
     // FIXME: This should never happen.
     if (!Entry)
       return Include;
 
     bool IsSystem;
     std::string Suggestion =
         HeaderSearch.suggestPathToFileForDiagnostics(Entry, &IsSystem);
-
+    // Falls back to orignal file path if fails.
+    if (Suggestion == PathRelativeToBuildDir)
+      Suggestion = StrippedInclude;
     return IsSystem ? '<' + Suggestion + '>' : '"' + Suggestion + '"';
   }
 
   /// Generate replacements for the suggested includes.
   /// \return true if changes will be made, false otherwise.
   bool Rewrite(clang::SourceManager &SourceManager,
                clang::HeaderSearch &HeaderSearch,
                std::vector<clang::tooling::Replacement> &replacements) {

test/include-fixer/Inputs/database_template.json

+[
+{
+  "directory": "test_dir/build",
+  "command": "clang++ -I../include -o foo.o test_dir/src/foo.cpp",
+  "file": "test_dir/src/foo.cpp"
+}
+]

test/include-fixer/Inputs/yaml_db_template.yaml

+---
+Name:           foo
+Contexts:
+  - ContextType:     Namespace
+    ContextName:     a
+  - ContextType:     Namespace
+    ContextName:     b
+FilePath:        test_dir/foo.h
+LineNumber:      1
+Type:            Class
+...

test/include-fixer/include_path.cpp

+// REQUIRES: shell
+// RUN: mkdir -p %T/include-fixer/include
+// RUN: mkdir -p %T/include-fixer/build
+// RUN: mkdir -p %T/include-fixer/src
+// RUN: sed 's|test_dir|%T/include-fixer|g' %S/Inputs/database_template.json > %T/include-fixer/build/compile_commands.json
+// RUN: sed 's|test_dir|%T/include-fixer/include|g' %S/Inputs/yaml_db_template.yaml > %T/include-fixer/build/fake_yaml_db.yaml
+// RUN: echo 'b::a::foo f;' > %T/include-fixer/src/foo.cpp
+// RUN: touch %T/include-fixer/include/foo.h
+// RUN: cd %T/include-fixer/build
+// RUN: clang-include-fixer -db=yaml -input=fake_yaml_db.yaml -p=. %T/include-fixer/src/foo.cpp
+// RUN: FileCheck -input-file=%T/include-fixer/src/foo.cpp %s
+
+// CHECK: #include "foo.h"
+// CHECK: b::a::foo f;