Merge pull request #17665 from allevato/debug-prefix-map-wip

Implement -debug-prefix-map flag.

include/swift/Basic/PathRemapper.h

@@ -0,0 +1,63 @@
+//===--- PathRemapper.h - Transforms path prefixes --------------*- C++ -*-===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2018 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 defines a data structure that stores a string-to-string
+//  mapping used to transform file paths based on a prefix mapping. It
+//  is optimized for the common case, which is that there will be
+//  extremely few mappings (i.e., one or two).
+//
+//  Remappings are stored such that they are applied in the order they
+//  are passed on the command line. This would only matter if one
+//  source mapping was a prefix of another.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef SWIFT_BASIC_PATHREMAPPER_H
+#define SWIFT_BASIC_PATHREMAPPER_H
+
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Twine.h"
+
+#include <string>
+#include <utility>
+
+namespace swift {
+
+class PathRemapper {
+  SmallVector<std::pair<std::string, std::string>, 2> PathMappings;
+
+public:
+  /// Adds a mapping such that any paths starting with `FromPrefix` have that
+  /// portion replaced with `ToPrefix`.
+  void addMapping(StringRef FromPrefix, StringRef ToPrefix) {
+    PathMappings.emplace_back(FromPrefix, ToPrefix);
+  }
+
+  /// Returns a remapped `Path` if it starts with a prefix in the map; otherwise
+  /// the original path is returned.
+  std::string remapPath(StringRef Path) const {
+    // Clang's implementation of this feature also compares the path string
+    // directly instead of treating path segments as indivisible units. The
+    // latter would arguably be more accurate, but we choose to preserve
+    // compatibility with Clang (especially because we propagate the flag to
+    // ClangImporter as well).
+    for (const auto &Mapping : PathMappings)
+      if (Path.startswith(Mapping.first))
+        return (Twine(Mapping.second) +
+                Path.substr(Mapping.first.size())).str();
+    return Path.str();
+  }
+};
+
+} // end namespace swift
+
+#endif // SWIFT_BASIC_PATHREMAPPER_H