feat: add git integration for 3-way merge and fix path handling

- Add base content support for 3-way merge operations
- Integrate git commands to fetch base and ours content
- Make filename required for git operations
- Fix file paths to use relative instead of absolute paths
- Improve conflict detection for identical ours/theirs cases

Author: mayank1513

.changeset/git-integration-and-path-fixes.md

@@ -0,0 +1,11 @@
+---
+"git-json-resolver": minor
+---
+
+Add Git integration for 3-way merge support and fix file path handling
+
+- Add base content support to ParsedConflict interface for 3-way merges
+- Integrate Git commands to fetch base and ours content when parsing conflicts
+- Make filename parameter required in ParseConflictOptions for Git operations
+- Fix file path handling in utils to return relative paths instead of absolute paths
+- Improve conflict detection for cases where ours and theirs are identical

lib/src/file-parser.ts

@@ -1,4 +1,8 @@
+import { execFile } from "node:child_process";
 import { Config, SupportedParsers } from "./types";
+import { promisify } from "node:util";
+
+const execFileAsync = promisify(execFile);
 
 /**
  * Represents a parsed conflict from a file with `ours` and `theirs` versions.
@@ -10,6 +14,8 @@ export interface ParsedConflict<T = unknown> {
   ours: T;
   /** Parsed content from the "theirs" side of the conflict. */
   theirs: T;
+  /** Parsed content from the "base" side of the conflict (optional). */
+  base?: T;
   /** Format used to parse the content (`json`, `yaml`, `toml`, `xml`, or `custom`). */
   format: string;
 }
@@ -19,14 +25,14 @@ export interface ParsedConflict<T = unknown> {
  */
 export interface ParseConflictOptions extends Pick<Config, "parsers"> {
   /**
-   * Optional filename hint to prioritize parser choice.
+   * filename hint to prioritize parser choice as well as get base and ours from git.
    * Example:
    * - `config.yaml` → try `yaml` first.
    * - `data.toml` → try `toml` first.
    *
    * If extension is unknown, falls back to `parsers` or `"json"`.
    */
-  filename?: string;
+  filename: string;
 }
 
 /**
@@ -48,7 +54,7 @@ export interface ParseConflictOptions extends Pick<Config, "parsers"> {
  */
 export const parseConflictContent = async <T = unknown>(
   content: string,
-  options: ParseConflictOptions = {},
+  options: ParseConflictOptions,
 ): Promise<ParsedConflict<T>> => {
   const lines = content.split("\n");
   const oursLines: string[] = [];
@@ -87,8 +93,23 @@ export const parseConflictContent = async <T = unknown>(
     }
   }
 
-  const oursRaw = oursLines.join("\n");
+  let oursRaw = oursLines.join("\n");
   const theirsRaw = theirsLines.join("\n");
+  const baseRaw = await execFileAsync("git", ["show", `:1:${options.filename}`], {
+    maxBuffer: 1024 * 1024 * 50,
+  })
+    .then(({ stdout }) => stdout)
+    .catch(() => null);
+
+  // No conflict
+  if (oursRaw === theirsRaw) {
+    oursRaw =
+      (await execFileAsync("git", ["show", `HEAD:${options.filename}`], {
+        maxBuffer: 1024 * 1024 * 50,
+      })
+        .then(({ stdout }) => stdout)
+        .catch(() => null)) ?? oursRaw;
+  }
 
   if (!oursRaw || !theirsRaw) {
     throw new Error("Conflict parsing resulted in empty content.");
@@ -98,11 +119,14 @@ export const parseConflictContent = async <T = unknown>(
   const parsers = normalizeParsers(options);
 
   const [oursParsed, format] = await runParser(oursRaw, parsers);
-  const [theirsParsed] = await runParser(theirsRaw, [format]);
+  const [[theirsParsed], baseParsed] = await Promise.all(
+    (baseRaw ? [theirsRaw, baseRaw] : [theirsRaw]).map(raw => runParser(raw, [format])),
+  );
 
   return {
     ours: oursParsed as T,
     theirs: theirsParsed as T,
+    base: baseParsed?.[0] as T | undefined,
     format: typeof format === "string" ? format : format.name,
   };
 };

lib/src/utils.ts

@@ -75,21 +75,19 @@ export const listMatchingFiles = async ({
 
     for (const entry of entries) {
       const fullPath = path.join(dir, entry.name);
+      const relativePath = path.relative(root, fullPath);
 
       if (entry.isDirectory()) {
         /* v8 ignore next */
-        if (
-          !/node_modules|\.git/.test(entry.name) &&
-          !skipDirMatcher(path.relative(root, fullPath))
-        ) {
+        if (!/node_modules|\.git/.test(entry.name) && !skipDirMatcher(relativePath)) {
           await walk(fullPath);
         }
-      } else if (fileMatcher(path.relative(root, fullPath))) {
+      } else if (fileMatcher(relativePath)) {
         try {
           const content = await fs.readFile(fullPath, "utf8");
 
           if (includeNonConflicted || hasConflict(content)) {
-            fileEntries.push({ filePath: fullPath, content });
+            fileEntries.push({ filePath: relativePath, content });
             /* v8 ignore next 6 -- Logging and warning only */
           } else if (debug) {
             console.info(`Skipped (no conflicts): ${fullPath}`);