Rewrite applyPatch

README.md

@@ -119,13 +119,21 @@ Broadly, jsdiff's diff functions all take an old text and a new text and perform
 
 * `Diff.applyPatch(source, patch[, options])` - attempts to apply a unified diff patch.
 
-    If the patch was applied successfully, returns a string containing the patched text. If the patch could not be applied (because some hunks in the patch couldn't be fitted to the text in `source`), returns false.
+    Hunks are applied first to last. `applyPatch` first tries to apply the first hunk at the line number specified in the hunk header, and with all context lines matching exactly. If that fails, it tries scanning backwards and forwards, one line at a time, to find a place to apply the hunk where the context lines match exactly. If that still fails, and `fuzzFactor` is greater than zero, it increments the maximum number of mismatches (missing, extra, or changed context lines) that there can be between the hunk context and a region where we are trying to apply the patch such that the hunk will still be considered to match. Regardless of `fuzzFactor`, lines to be deleted in the hunk *must* be present for a hunk to match, and the context lines *immediately* before and after an insertion must match exactly.
+
+    Once a hunk is successfully fitted, the process begins again with the next hunk. Regardless of `fuzzFactor`, later hunks must be applied later in the file than earlier hunks.
+
+    If a hunk cannot be successfully fitted *anywhere* with fewer than `fuzzFactor` mismatches, `applyPatch` fails and returns `false`.
+
+    If a hunk is successfully fitted but not at the line number specified by the hunk header, all subsequent hunks have their target line number adjusted accordingly. (e.g. if the first hunk is applied 10 lines below where the hunk header said it should fit, `applyPatch` will *start* looking for somewhere to apply the second hunk 10 lines below where its hunk header says it goes.)
+
+    If the patch was applied successfully, returns a string containing the patched text. If the patch could not be applied (because some hunks in the patch couldn't be fitted to the text in `source`), `applyPatch` returns false.
 
     `patch` may be a string diff or the output from the `parsePatch` or `structuredPatch` methods.
 
     The optional `options` object may have the following keys:
 
-    - `fuzzFactor`: Number of lines that are allowed to differ before rejecting a patch. Defaults to 0.
+    - `fuzzFactor`: Maximum Levenshtein distance (in lines deleted, added, or subtituted) between the context shown in a patch hunk and the lines found in the file. Defaults to 0.
     - `autoConvertLineEndings`: If `true`, and if the file to be patched consistently uses different line endings to the patch (i.e. either the file always uses Unix line endings while the patch uses Windows ones, or vice versa), then `applyPatch` will behave as if the line endings in the patch were the same as those in the source file. (If `false`, the patch will usually fail to apply in such circumstances since lines deleted in the patch won't be considered to match those in the source file.) Defaults to `true`.
     - `compareLine(lineNumber, line, operation, patchContent)`: Callback used to compare to given lines to determine if they should be considered equal when patching. Defaults to strict equality but may be overridden to provide fuzzier comparison. Should return false if the lines should be rejected.
 

release-notes.md

@@ -28,6 +28,10 @@
 - [#521](https://github.com/kpdecker/jsdiff/pull/521) **the `callback` option is now supported by `structuredPatch`, `createPatch
 - [#529](https://github.com/kpdecker/jsdiff/pull/529) **`parsePatch` can now parse patches where lines starting with `--` or `++` are deleted/inserted**; previously, there were edge cases where the parser would choke on valid patches or give wrong results.
 - [#530](https://github.com/kpdecker/jsdiff/pull/530) **Added `ignoreNewlineAtEof` option` to `diffLines`**
+- [#533](https://github.com/kpdecker/jsdiff/pull/533) **`applyPatch` uses an entirely new algorithm for fuzzy matching.** Differences between the old and new algorithm are as follows:
+  * The `fuzzFactor` now indicates the maximum [*Levenshtein* distance](https://en.wikipedia.org/wiki/Levenshtein_distance) that there can be between the context shown in a hunk and the actual file content at a location where we try to apply the hunk. (Previously, it represented a maximum [*Hamming* distance](https://en.wikipedia.org/wiki/Hamming_distance), meaning that a single insertion or deletion in the source file could stop a hunk from applying even with a high `fuzzFactor`.)
+  * A hunk containing a deletion can now only be applied in a context where the line to be deleted actually appears verbatim. (Previously, as long as enough context lines in the hunk matched, `applyPatch` would apply the hunk anyway and delete a completely different line.)
+  * The context line immediately before and immediately after an insertion must match exactly between the hunk and the file for a hunk to apply. (Previously this was not required.)
 
 ## v5.2.0
 

src/patch/apply.js

@@ -29,104 +29,228 @@ export function applyPatch(source, uniDiff, options = {}) {
       hunks = uniDiff.hunks,
 
       compareLine = options.compareLine || ((lineNumber, line, operation, patchContent) => line === patchContent),
-      errorCount = 0,
       fuzzFactor = options.fuzzFactor || 0,
-      minLine = 0,
-      offset = 0,
+      minLine = 0;
 
-      removeEOFNL,
-      addEOFNL;
+  if (fuzzFactor < 0 || !Number.isInteger(fuzzFactor)) {
+    throw new Error('fuzzFactor must be a non-negative integer');
+  }
+
+  // Special case for empty patch.
+  if (!hunks.length) {
+    return source;
+  }
+
+  // Before anything else, handle EOFNL insertion/removal. If the patch tells us to make a change
+  // to the EOFNL that is redundant/impossible - i.e. to remove a newline that's not there, or add a
+  // newline that already exists - then we either return false and fail to apply the patch (if
+  // fuzzFactor is 0) or simply ignore the problem and do nothing (if fuzzFactor is >0).
+  // If we do need to remove/add a newline at EOF, this will always be in the final hunk:
+  let prevLine = '',
+      removeEOFNL = false,
+      addEOFNL = false;
+  for (let i = 0; i < hunks[hunks.length - 1].lines.length; i++) {
+    const line = hunks[hunks.length - 1].lines[i];
+    if (line[0] == '\\') {
+      if (prevLine[0] == '+') {
+        removeEOFNL = true;
+      } else if (prevLine[0] == '-') {
+        addEOFNL = true;
+      }
+      break;
+    }
+    prevLine = line;
+  }
+  if (removeEOFNL) {
+    if (lines[lines.length - 1] == '') {
+      lines.pop();
+    } else if (!fuzzFactor) {
+      return false;
+    }
+  } else if (addEOFNL) {
+    if (lines[lines.length - 1] != '') {
+      lines.push('');
+    } else if (!fuzzFactor) {
+      return false;
+    }
+  }
 
   /**
-   * Checks if the hunk exactly fits on the provided location
+   * Checks if the hunk can be made to fit at the provided location with at most `maxErrors`
+   * insertions, substitutions, or deletions, while ensuring also that:
+   * - lines deleted in the hunk match exactly, and
+   * - wherever an insertion operation or block of insertion operations appears in the hunk, the
+   *   immediately preceding and following lines of context match exactly
+   *
+   * `toPos` should be set such that lines[toPos] is meant to match hunkLines[0].
+   *
+   * If the hunk can be applied, returns an object with properties `oldLineLastI` and
+   * `replacementLines`. Otherwise, returns null.
    */
-  function hunkFits(hunk, toPos) {
-    for (let j = 0; j < hunk.lines.length; j++) {
-      let line = hunk.lines[j],
-          operation = (line.length > 0 ? line[0] : ' '),
-          content = (line.length > 0 ? line.substr(1) : line);
-
-      if (operation === ' ' || operation === '-') {
-        // Context sanity check
-        if (!compareLine(toPos + 1, lines[toPos], operation, content)) {
-          errorCount++;
-
-          if (errorCount > fuzzFactor) {
-            return false;
+  function applyHunk(
+    hunkLines,
+    toPos,
+    maxErrors,
+    hunkLinesI = 0,
+    lastContextLineMatched = true,
+    patchedLines = [],
+    patchedLinesLength = 0,
+  ) {
+    let nConsecutiveOldContextLines = 0;
+    let nextContextLineMustMatch = false;
+    for (; hunkLinesI < hunkLines.length; hunkLinesI++) {
+      let hunkLine = hunkLines[hunkLinesI],
+          operation = (hunkLine.length > 0 ? hunkLine[0] : ' '),
+          content = (hunkLine.length > 0 ? hunkLine.substr(1) : hunkLine);
+
+      if (operation === '-') {
+        if (compareLine(toPos + 1, lines[toPos], operation, content)) {
+          toPos++;
+          nConsecutiveOldContextLines = 0;
+        } else {
+          if (!maxErrors || lines[toPos] == null) {
+            return null;
           }
+          patchedLines[patchedLinesLength] = lines[toPos];
+          return applyHunk(
+            hunkLines,
+            toPos + 1,
+            maxErrors - 1,
+            hunkLinesI,
+            false,
+            patchedLines,
+            patchedLinesLength + 1,
+          );
+        }
+      }
+
+      if (operation === '+') {
+        if (!lastContextLineMatched) {
+          return null;
+        }
+        patchedLines[patchedLinesLength] = content;
+        patchedLinesLength++;
+        nConsecutiveOldContextLines = 0;
+        nextContextLineMustMatch = true;
+      }
+
+      if (operation === ' ') {
+        nConsecutiveOldContextLines++;
+        patchedLines[patchedLinesLength] = lines[toPos];
+        if (compareLine(toPos + 1, lines[toPos], operation, content)) {
+          patchedLinesLength++;
+          lastContextLineMatched = true;
+          nextContextLineMustMatch = false;
+          toPos++;
+        } else {
+          if (nextContextLineMustMatch || !maxErrors) {
+            return null;
+          }
+
+          // Consider 3 possibilities in sequence:
+          // 1. lines contains a *substitution* not included in the patch context, or
+          // 2. lines contains an *insertion* not included in the patch context, or
+          // 3. lines contains a *deletion* not included in the patch context
+          // The first two options are of course only possible if the line from lines is non-null -
+          // i.e. only option 3 is possible if we've overrun the end of the old file.
+          return (
+            lines[toPos] && (
+              applyHunk(
+                hunkLines,
+                toPos + 1,
+                maxErrors - 1,
+                hunkLinesI + 1,
+                false,
+                patchedLines,
+                patchedLinesLength + 1
+              ) || applyHunk(
+                hunkLines,
+                toPos + 1,
+                maxErrors - 1,
+                hunkLinesI,
+                false,
+                patchedLines,
+                patchedLinesLength + 1
+              )
+            ) || applyHunk(
+              hunkLines,
+              toPos,
+              maxErrors - 1,
+              hunkLinesI + 1,
+              false,
+              patchedLines,
+              patchedLinesLength
+            )
+          );
         }
-        toPos++;
       }
     }
 
-    return true;
+    // Before returning, trim any unmodified context lines off the end of patchedLines and reduce
+    // toPos (and thus oldLineLastI) accordingly. This allows later hunks to be applied to a region
+    // that starts in this hunk's trailing context.
+    patchedLinesLength -= nConsecutiveOldContextLines;
+    toPos -= nConsecutiveOldContextLines;
+    patchedLines.length = patchedLinesLength;
+    return {
+      patchedLines,
+      oldLineLastI: toPos - 1
+    };
   }
 
+  const resultLines = [];
+
   // Search best fit offsets for each hunk based on the previous ones
+  let prevHunkOffset = 0;
   for (let i = 0; i < hunks.length; i++) {
-    let hunk = hunks[i],
-        maxLine = lines.length - hunk.oldLines,
-        localOffset = 0,
-        toPos = offset + hunk.oldStart - 1;
-
-    let iterator = distanceIterator(toPos, minLine, maxLine);
-
-    for (; localOffset !== undefined; localOffset = iterator()) {
-      if (hunkFits(hunk, toPos + localOffset)) {
-        hunk.offset = offset += localOffset;
+    const hunk = hunks[i];
+    let hunkResult;
+    let maxLine = lines.length - hunk.oldLines + fuzzFactor;
+    let toPos;
+    for (let maxErrors = 0; maxErrors <= fuzzFactor; maxErrors++) {
+      toPos = hunk.oldStart + prevHunkOffset - 1;
+      let iterator = distanceIterator(toPos, minLine, maxLine);
+      for (; toPos !== undefined; toPos = iterator()) {
+        hunkResult = applyHunk(hunk.lines, toPos, maxErrors);
+        if (hunkResult) {
+          break;
+        }
+      }
+      if (hunkResult) {
         break;
       }
     }
 
-    if (localOffset === undefined) {
+    if (!hunkResult) {
       return false;
     }
 
-    // Set lower text limit to end of the current hunk, so next ones don't try
-    // to fit over already patched text
-    minLine = hunk.offset + hunk.oldStart + hunk.oldLines;
-  }
+    // Copy everything from the end of where we applied the last hunk to the start of this hunk
+    for (let i = minLine; i < toPos; i++) {
+      resultLines.push(lines[i]);
+    }
 
-  // Apply patch hunks
-  let diffOffset = 0;
-  for (let i = 0; i < hunks.length; i++) {
-    let hunk = hunks[i],
-        toPos = hunk.oldStart + hunk.offset + diffOffset - 1;
-    diffOffset += hunk.newLines - hunk.oldLines;
+    // Add the lines produced by applying the hunk:
+    for (let i = 0; i < hunkResult.patchedLines.length; i++) {
+      const line = hunkResult.patchedLines[i];
+      resultLines.push(line);
+    }
 
-    for (let j = 0; j < hunk.lines.length; j++) {
-      let line = hunk.lines[j],
-          operation = (line.length > 0 ? line[0] : ' '),
-          content = (line.length > 0 ? line.substr(1) : line);
+    // Set lower text limit to end of the current hunk, so next ones don't try
+    // to fit over already patched text
+    minLine = hunkResult.oldLineLastI + 1;
 
-      if (operation === ' ') {
-        toPos++;
-      } else if (operation === '-') {
-        lines.splice(toPos, 1);
-      /* istanbul ignore else */
-      } else if (operation === '+') {
-        lines.splice(toPos, 0, content);
-        toPos++;
-      } else if (operation === '\\') {
-        let previousOperation = hunk.lines[j - 1] ? hunk.lines[j - 1][0] : null;
-        if (previousOperation === '+') {
-          removeEOFNL = true;
-        } else if (previousOperation === '-') {
-          addEOFNL = true;
-        }
-      }
-    }
+    // Note the offset between where the patch said the hunk should've applied and where we
+    // applied it, so we can adjust future hunks accordingly:
+    prevHunkOffset = toPos + 1 - hunk.oldStart;
   }
 
-  // Handle EOFNL insertion/removal
-  if (removeEOFNL) {
-    while (!lines[lines.length - 1]) {
-      lines.pop();
-    }
-  } else if (addEOFNL) {
-    lines.push('');
+  // Copy over the rest of the lines from the old text
+  for (let i = minLine; i < lines.length; i++) {
+    resultLines.push(lines[i]);
   }
-  return lines.join('\n');
+
+  return resultLines.join('\n');
 }
 
 // Wrapper that supports multiple file patches via callbacks.

src/util/distance-iterator.js

@@ -18,7 +18,7 @@ export default function(start, minLine, maxLine) {
       // Check if trying to fit beyond text length, and if not, check it fits
       // after offset location (or desired location on first iteration)
       if (start + localOffset <= maxLine) {
-        return localOffset;
+        return start + localOffset;
       }
 
       forwardExhausted = true;
@@ -32,7 +32,7 @@ export default function(start, minLine, maxLine) {
       // Check if trying to fit before text beginning, and if not, check it fits
       // before offset location
       if (minLine <= start - localOffset) {
-        return -localOffset++;
+        return start - localOffset++;
       }
 
       backwardExhausted = true;