Add better support for Git's patch format

src/patch/parse.ts

@@ -1,5 +1,232 @@
 import type { StructuredPatch } from '../types.js';
 
+/**
+ * Parse a single Git path token starting at the provided index.
+ * Supports C-style quoted paths used by Git when `core.quotePath` is enabled.
+ */
+function parseGitPathToken(input: string, startIndex: number): { value: string; nextIndex: number } | null {
+  let i = startIndex;
+  while (i < input.length && input[i] === ' ') {
+    i++;
+  }
+  if (i >= input.length) {
+    return null;
+  }
+  if (input[i] === '"') {
+    i++;
+    let value = '';
+    while (i < input.length) {
+      const ch = input[i];
+      if (ch === '"') {
+        return { value, nextIndex: i + 1 };
+      }
+      if (ch === '\\') {
+        i++;
+        if (i >= input.length) {
+          return null;
+        }
+        const esc = input[i];
+        if (esc >= '0' && esc <= '7') {
+          let octal = esc;
+          for (let count = 0; count < 2; count++) {
+            const next = input[i + 1];
+            if (next >= '0' && next <= '7') {
+              i++;
+              octal += next;
+            } else {
+              break;
+            }
+          }
+          value += String.fromCharCode(parseInt(octal, 8));
+          i++;
+          continue;
+        }
+        if (esc === 'x') {
+          const hex = input.substring(i + 1, i + 3);
+          if (/^[0-9a-fA-F]{2}$/.test(hex)) {
+            value += String.fromCharCode(parseInt(hex, 16));
+            i += 3;
+            continue;
+          }
+          value += 'x';
+          i++;
+          continue;
+        }
+        switch (esc) {
+          case 'n':
+            value += '\n';
+            break;
+          case 't':
+            value += '\t';
+            break;
+          case 'r':
+            value += '\r';
+            break;
+          case 'b':
+            value += '\b';
+            break;
+          case 'f':
+            value += '\f';
+            break;
+          case 'a':
+            value += '\u0007';
+            break;
+          case 'v':
+            value += '\u000b';
+            break;
+          case '\\':
+            value += '\\';
+            break;
+          case '"':
+            value += '"';
+            break;
+          default:
+            value += esc;
+        }
+        i++;
+        continue;
+      }
+      value += ch;
+      i++;
+    }
+    return null;
+  }
+  const start = i;
+  while (i < input.length && input[i] !== ' ') {
+    i++;
+  }
+  return { value: input.substring(start, i), nextIndex: i };
+}
+
+/**
+ * Parse a fixed number of Git path tokens from a string.
+ */
+function parseGitPathTokens(input: string, count: number): string[] | null {
+  let index = 0;
+  const paths: string[] = [];
+  for (let parsed = 0; parsed < count; parsed++) {
+    const token = parseGitPathToken(input, index);
+    if (!token) {
+      return null;
+    }
+    paths.push(token.value);
+    index = token.nextIndex;
+  }
+  return paths;
+}
+
+/**
+ * Parse unquoted Git diff paths separated by the ` b/` marker.
+ * If multiple splits are possible, prefer a split where old and new paths match.
+ * If no matching split exists, use the last possible split.
+ */
+function parseGitUnquotedDiffPaths(input: string): { oldPath: string; newPath: string } | null {
+  if (!input.startsWith('a/')) {
+    return null;
+  }
+  const candidates: Array<{ oldPath: string; newPath: string }> = [];
+  const matchingCandidates: Array<{ oldPath: string; newPath: string }> = [];
+  let searchIndex = 0;
+  while (searchIndex < input.length) {
+    const separatorIndex = input.indexOf(' b/', searchIndex);
+    if (separatorIndex === -1) {
+      break;
+    }
+    const oldPath = input.substring(0, separatorIndex);
+    const newPath = input.substring(separatorIndex + 1);
+    if (oldPath.startsWith('a/') && newPath.startsWith('b/')) {
+      const candidate = { oldPath, newPath };
+      candidates.push(candidate);
+      if (oldPath.substring(2) === newPath.substring(2)) {
+        matchingCandidates.push(candidate);
+      }
+    }
+    searchIndex = separatorIndex + 1;
+  }
+  if (matchingCandidates.length === 1) {
+    return matchingCandidates[0];
+  }
+  if (matchingCandidates.length > 1) {
+    return matchingCandidates[matchingCandidates.length - 1];
+  }
+  if (candidates.length) {
+    return candidates[candidates.length - 1];
+  }
+  return null;
+}
+
+/**
+ * Parse a Git `diff --git a/... b/...` header into old/new file names.
+ */
+function parseGitDiffHeader(line: string): { oldFileName?: string; newFileName?: string } | null {
+  const prefix = 'diff --git ';
+  if (!line.startsWith(prefix)) {
+    return null;
+  }
+  const rawPaths = line.substring(prefix.length);
+  let oldFileName: string | undefined;
+  let newFileName: string | undefined;
+
+  if (rawPaths.startsWith('"')) {
+    const firstToken = parseGitPathToken(rawPaths, 0);
+    if (!firstToken) {
+      return null;
+    }
+    oldFileName = firstToken.value;
+    const remainder = rawPaths.substring(firstToken.nextIndex).trimStart();
+    if (!remainder.length) {
+      return null;
+    }
+    if (remainder.startsWith('"')) {
+      const secondToken = parseGitPathToken(remainder, 0);
+      if (!secondToken) {
+        return null;
+      }
+      newFileName = secondToken.value;
+    } else {
+      newFileName = remainder;
+    }
+  } else {
+    const unquoted = parseGitUnquotedDiffPaths(rawPaths);
+    if (unquoted) {
+      oldFileName = unquoted.oldPath;
+      newFileName = unquoted.newPath;
+    } else {
+      const paths = parseGitPathTokens(rawPaths, 2);
+      if (!paths) {
+        return null;
+      }
+      [oldFileName, newFileName] = paths;
+    }
+  }
+
+  if (oldFileName.startsWith('a/')) {
+    oldFileName = oldFileName.substring(2);
+  }
+  if (newFileName.startsWith('b/')) {
+    newFileName = newFileName.substring(2);
+  }
+  return { oldFileName, newFileName };
+}
+
+/**
+ * Parse extended Git headers like `rename from`, `rename to`, `copy from`, and `copy to`.
+ */
+function parseGitExtendedPath(line: string, prefix: string): string | null {
+  if (!line.startsWith(prefix)) {
+    return null;
+  }
+  const remainder = line.substring(prefix.length).trimStart();
+  if (!remainder.length) {
+    return null;
+  }
+  if (remainder.startsWith('"')) {
+    const token = parseGitPathToken(remainder, 0);
+    return token ? token.value : null;
+  }
+  return remainder;
+}
+
 /**
  * Parses a patch into structured data, in the same structure returned by `structuredPatch`.
  *
@@ -12,6 +239,7 @@ export function parsePatch(uniDiff: string): StructuredPatch[] {
 
   function parseIndex() {
     const index: Partial<StructuredPatch> = {};
+    let seenGitHeader = false;
     list.push(index);
 
     // Parse diff metadata
@@ -23,6 +251,56 @@ export function parsePatch(uniDiff: string): StructuredPatch[] {
         break;
       }
 
+      const gitHeader = parseGitDiffHeader(line);
+      if (gitHeader) {
+        if (seenGitHeader || index.index || index.oldFileName || index.newFileName) {
+          break;
+        }
+        seenGitHeader = true;
+        if (gitHeader.oldFileName) {
+          index.oldFileName = gitHeader.oldFileName;
+        }
+        if (gitHeader.newFileName) {
+          index.newFileName = gitHeader.newFileName;
+          if (!index.index) {
+            index.index = gitHeader.newFileName;
+          }
+        }
+        i++;
+        continue;
+      }
+
+      const renameFrom = parseGitExtendedPath(line, 'rename from ');
+      if (renameFrom) {
+        index.oldFileName = renameFrom;
+        i++;
+        continue;
+      }
+      const renameTo = parseGitExtendedPath(line, 'rename to ');
+      if (renameTo) {
+        index.newFileName = renameTo;
+        if (!index.index) {
+          index.index = renameTo;
+        }
+        i++;
+        continue;
+      }
+      const copyFrom = parseGitExtendedPath(line, 'copy from ');
+      if (copyFrom) {
+        index.oldFileName = copyFrom;
+        i++;
+        continue;
+      }
+      const copyTo = parseGitExtendedPath(line, 'copy to ');
+      if (copyTo) {
+        index.newFileName = copyTo;
+        if (!index.index) {
+          index.index = copyTo;
+        }
+        i++;
+        continue;
+      }
+
       // Try to parse the line as a diff header, like
       //     Index: README.md
       // or