[incrParse] Fix bug in translation of post-edit to pre-edit positions

Author: ahoppen

include/swift/Parse/SyntaxParsingCache.h

@@ -18,7 +18,9 @@
 #include "llvm/Support/raw_ostream.h"
 #include <unordered_set>
 
-namespace {
+namespace swift {
+
+using namespace swift::syntax;
 
 /// A single edit to the original source file in which a continuous range of
 /// characters have been replaced by a new string
@@ -42,12 +44,6 @@ struct SourceEdit {
   }
 };
 
-} // anonymous namespace
-
-namespace swift {
-
-using namespace swift::syntax;
-
 struct SyntaxReuseRegion {
   AbsolutePosition Start;
   AbsolutePosition End;
@@ -89,6 +85,13 @@ class SyntaxParsingCache {
   std::vector<SyntaxReuseRegion>
   getReusedRegions(const SourceFileSyntax &SyntaxTree) const;
 
+  /// Translates a post-edit position to a pre-edit position by undoing the
+  /// specified edits.
+  /// Should not be invoked externally. Only public for testing purposes.
+  static size_t
+  translateToPreEditPosition(size_t PostEditPosition,
+                             llvm::SmallVector<SourceEdit, 4> Edits);
+
 private:
   llvm::Optional<Syntax> lookUpFrom(const Syntax &Node, size_t NodeStart,
                                     size_t Position, SyntaxKind Kind);

lib/Parse/SyntaxParsingCache.cpp

@@ -79,17 +79,21 @@ llvm::Optional<Syntax> SyntaxParsingCache::lookUpFrom(const Syntax &Node,
   return llvm::None;
 }
 
-llvm::Optional<Syntax> SyntaxParsingCache::lookUp(size_t NewPosition,
-                                                  SyntaxKind Kind) {
-  // Undo the edits in reverse order
-  size_t OldPosition = NewPosition;
-  for (auto I = Edits.rbegin(), E = Edits.rend(); I != E; ++I) {
+size_t SyntaxParsingCache::translateToPreEditPosition(
+    size_t PostEditPosition, llvm::SmallVector<SourceEdit, 4> Edits) {
+  size_t Position = PostEditPosition;
+  for (auto I = Edits.begin(), E = Edits.end(); I != E; ++I) {
     auto Edit = *I;
-    if (Edit.End < OldPosition) {
-      OldPosition =
-          OldPosition - Edit.ReplacementLength + Edit.originalLength();
+    if (Edit.End + Edit.ReplacementLength - Edit.originalLength() <= Position) {
+      Position = Position - Edit.ReplacementLength + Edit.originalLength();
     }
   }
+  return Position;
+}
+
+llvm::Optional<Syntax> SyntaxParsingCache::lookUp(size_t NewPosition,
+                                                  SyntaxKind Kind) {
+  size_t OldPosition = translateToPreEditPosition(NewPosition, Edits);
 
   auto Node = lookUpFrom(OldSyntaxTree, /*NodeStart=*/0, OldPosition, Kind);
   if (Node.hasValue()) {

unittests/Parse/CMakeLists.txt

@@ -2,6 +2,7 @@ add_swift_unittest(SwiftParseTests
   BuildConfigTests.cpp
   LexerTests.cpp
   LexerTriviaTests.cpp
+  SyntaxParsingCacheTests.cpp
   TokenizerTests.cpp
 )
 

unittests/Parse/SyntaxParsingCacheTests.cpp

@@ -0,0 +1,119 @@
+#include "swift/Parse/SyntaxParsingCache.h"
+#include "gtest/gtest.h"
+
+using namespace swift;
+using namespace llvm;
+
+class TranslateToPreEditPositionTest : public ::testing::Test {};
+
+TEST_F(TranslateToPreEditPositionTest, SingleEditBefore) {
+  // Old: ab_xy
+  // New: a1b_xy
+  //
+  // Edits:
+  // (1) 1-2: a -> a1
+  //
+  // Lookup for _ at new position 4
+
+  llvm::SmallVector<SourceEdit, 4> Edits = {
+      {1, 2, 2}
+  };
+
+  size_t PreEditPos = SyntaxParsingCache::translateToPreEditPosition(4, Edits);
+  EXPECT_EQ(PreEditPos, 3u);
+}
+
+TEST_F(TranslateToPreEditPositionTest, SingleEditDirectlyBefore) {
+  // Old: ab_xy
+  // New: ablah_xy
+  //
+  // Edits:
+  // (1) 2-3: b -> blah
+  //
+  // Lookup for _ at new position 6
+
+  llvm::SmallVector<SourceEdit, 4> Edits = {
+      {2, 3, 4}
+  };
+
+  size_t PreEditPos = SyntaxParsingCache::translateToPreEditPosition(6, Edits);
+  EXPECT_EQ(PreEditPos, 3u);
+}
+
+TEST_F(TranslateToPreEditPositionTest, SingleMultiCharacterEdit) {
+  // Old: ab_xy
+  // New: abcdef_xy
+  //
+  // Edits:
+  // (1) 1-3: ab -> abcdef
+  //
+  // Lookup for _ at new position 7
+
+  llvm::SmallVector<SourceEdit, 4> Edits = {
+      {1, 3, 6}
+  };
+
+  size_t PreEditPos = SyntaxParsingCache::translateToPreEditPosition(7, Edits);
+  EXPECT_EQ(PreEditPos, 3u);
+}
+
+TEST_F(TranslateToPreEditPositionTest, EditAfterLookup) {
+  // Old: ab_xy
+  // New: ab_xyz
+  //
+  // Edits:
+  // (1) 4-6: xy -> xyz
+  //
+  // Lookup for _ at new position 3
+
+  llvm::SmallVector<SourceEdit, 4> Edits = {{4, 6, 4}};
+
+  size_t PreEditPos = SyntaxParsingCache::translateToPreEditPosition(3, Edits);
+  EXPECT_EQ(PreEditPos, 3u);
+}
+
+TEST_F(TranslateToPreEditPositionTest, SimpleMultiEdit) {
+  // Old: ab_xy
+  // New: a1b2_x3y4
+  //
+  // Edits:
+  // (1) 1-2: a -> a1
+  // (2) 2-3: b -> b2
+  // (3) 4-5: x -> x3
+  // (4) 5-6: y -> y4
+  //
+  // Lookup for _ at new position 5
+
+  llvm::SmallVector<SourceEdit, 4> Edits = {
+      {1, 2, 2},
+      {2, 3, 2},
+      {4, 5, 2},
+      {5, 6, 2},
+  };
+
+  size_t PreEditPos = SyntaxParsingCache::translateToPreEditPosition(5, Edits);
+  EXPECT_EQ(PreEditPos, 3u);
+}
+
+TEST_F(TranslateToPreEditPositionTest, LongMultiEdit) {
+  // Old: ab_xy
+  // New: a11111b2_x3y4
+  //
+  // Edits:
+  // (1) 1-2: a -> a11111
+  // (2) 2-3: b -> b2
+  // (3) 4-5: x -> x3
+  // (4) 5-6: y -> y4
+  //
+  // Lookup for _ at new position
+
+  llvm::SmallVector<SourceEdit, 4> Edits = {
+      {1, 2, 6},
+      {2, 3, 2},
+      {4, 5, 2},
+      {5, 6, 2},
+  };
+
+  size_t PreEditPos = SyntaxParsingCache::translateToPreEditPosition(9, Edits);
+  EXPECT_EQ(PreEditPos, 3u);
+}