improve conflict complexity analysis and merge error messaging

src/commands/merge.ts

@@ -7,16 +7,40 @@ import { die } from "../fmt.ts"
 import { action as closeAction } from "./close.ts"
 
 const MAX_DIFF_LINES = 300
+const MAX_LOG_LINES = 50
+const MAX_STAT_LINES = 100
+const MAX_CONFLICT_REGIONS = 15
+const MAX_CONFLICTED_LINES = 200
 
-function lineCount(text: string): number {
-  if (!text) return 0
-  return text.split("\n").length
+interface ConflictAnalysis {
+  regions: number
+  conflictedLines: number
+}
+
+function analyzeConflicts(content: string): ConflictAnalysis {
+  let regions = 0
+  let conflictedLines = 0
+  let inConflict = false
+
+  for (const line of content.split("\n")) {
+    if (line.startsWith("<<<<<<<")) {
+      regions++
+      inConflict = true
+    } else if (line.startsWith(">>>>>>>")) {
+      inConflict = false
+    } else if (inConflict) {
+      conflictedLines++
+    }
+  }
+
+  return { regions, conflictedLines }
 }
 
 function truncate(text: string, maxLines = MAX_DIFF_LINES): string {
-  const count = lineCount(text)
-  if (count <= maxLines) return text
-  return text.split("\n").slice(0, maxLines).join("\n") + `\n... (truncated, ${count - maxLines} more lines)`
+  if (!text) return text
+  const lines = text.split("\n")
+  if (lines.length <= maxLines) return text
+  return lines.slice(0, maxLines).join("\n") + `\n... (truncated, ${lines.length - maxLines} more lines)`
 }
 
 export async function action(branch: string) {
@@ -49,22 +73,23 @@ export async function action(branch: string) {
     const branchLog = await git.commitLog(`${base}..${branch}`, root)
     const branchDiffStat = await git.diffStat(`${base}..${branch}`, root)
 
-    // Fetch diffs for all conflicted files and partition by complexity
+    // Read conflicted files, fetch diffs, and partition by complexity
     spin.text = "Checking conflict complexity"
-    const fileDiffs = await Promise.all(
+    const fileEntries = await Promise.all(
       conflicts.map(async (file) => {
-        const [oursDiff, theirsDiff] = await Promise.all([
+        const [content, oursDiff, theirsDiff] = await Promise.all([
+          Bun.file(join(root, file)).text(),
           git.fileDiff(base, "HEAD", file, root),
           git.fileDiff(base, branch, file, root),
         ])
-        return { file, oursDiff, theirsDiff }
+        return { file, content, oursDiff, theirsDiff, ...analyzeConflicts(content) }
       }),
     )
 
-    const resolvable: typeof fileDiffs = []
+    const resolvable: typeof fileEntries = []
     const skipped: string[] = []
-    for (const entry of fileDiffs) {
-      if (lineCount(entry.oursDiff) > MAX_DIFF_LINES || lineCount(entry.theirsDiff) > MAX_DIFF_LINES) {
+    for (const entry of fileEntries) {
+      if (entry.regions > MAX_CONFLICT_REGIONS || entry.conflictedLines > MAX_CONFLICTED_LINES) {
         skipped.push(entry.file)
       } else {
         resolvable.push(entry)
@@ -75,7 +100,9 @@ export async function action(branch: string) {
       spin.fail("All conflicts are too complex for auto-resolution")
       console.log("\nThe following files need manual resolution:")
       for (const file of skipped) console.log(`  - ${file}`)
-      console.log("\nResolve them manually, then run: git add <files> && git commit --no-edit")
+      console.log("\nYour repo is in a MERGING state. To finish:")
+      console.log("  Resolve the files, then run: git add <files> && git commit --no-edit")
+      console.log("  Or abort with: git merge --abort")
       return
     }
 
@@ -84,17 +111,15 @@ export async function action(branch: string) {
       `Merging branch \`${branch}\` into \`${current}\``,
       ``,
       `### Commits on \`${branch}\`:`,
-      (branchLog && truncate(branchLog, 50)) || "(no commits)",
+      (branchLog && truncate(branchLog, MAX_LOG_LINES)) || "(no commits)",
       ``,
       `### Overall changes on \`${branch}\`:`,
-      (branchDiffStat && truncate(branchDiffStat, 100)) || "(no changes)",
+      (branchDiffStat && truncate(branchDiffStat, MAX_STAT_LINES)) || "(no changes)",
     ].join("\n")
 
-    for (const { file, oursDiff, theirsDiff } of resolvable) {
+    for (const { file, content, oursDiff, theirsDiff } of resolvable) {
       spin.text = `Resolving ${file}`
 
-      const content = await Bun.file(join(root, file)).text()
-
       const context = [
         preamble,
         ``,
@@ -128,7 +153,9 @@ export async function action(branch: string) {
       spin.succeed(`Resolved ${resolvable.length} of ${conflicts.length} conflict(s)`)
       console.log("\nThe following files are too complex for auto-resolution:")
       for (const file of skipped) console.log(`  - ${file}`)
-      console.log("\nResolve them manually, then run: git add <files> && git commit --no-edit")
+      console.log("\nYour repo is in a MERGING state. To finish:")
+      console.log("  Resolve the remaining files, then run: git add <files> && git commit --no-edit")
+      console.log("  Or abort with: git merge --abort")
       return
     }
 

src/git.ts

@@ -149,12 +149,10 @@ export async function diffStat(range: string, cwd: string): Promise<string> {
   return result.text().trim()
 }
 
-/** Get the diff for a specific file between two refs. */
+/** Get the diff for a specific file between two refs. Returns empty string on failure. */
 export async function fileDiff(ref1: string, ref2: string, file: string, cwd: string): Promise<string> {
   const result = await $`git diff ${ref1} ${ref2} -- ${file}`.cwd(cwd).nothrow().quiet()
-  if (result.exitCode !== 0) {
-    throw new Error(`Failed to get diff for "${file}" between "${ref1}" and "${ref2}"`)
-  }
+  if (result.exitCode !== 0) return ""
   return result.text().trim()
 }