Truncate large diffs in merge context and add error handling to git log/diff helpers

src/commands/merge.ts

@@ -6,6 +6,12 @@ import { spinner } from "../spinner.ts"
 import { die } from "../fmt.ts"
 import { action as closeAction } from "./close.ts"
 
+function truncate(text: string, maxLines = 200): string {
+  const lines = text.split("\n")
+  if (lines.length <= maxLines) return text
+  return lines.slice(0, maxLines).join("\n") + `\n... (truncated, ${lines.length - maxLines} more lines)`
+}
+
 export async function action(branch: string) {
   const root = await git.repoRoot()
   const session = await state.getSession(root, branch)
@@ -33,14 +39,16 @@ export async function action(branch: string) {
     spin.text = "Gathering merge context"
     const current = await git.currentBranch(root)
     const base = await git.mergeBase("HEAD", branch, root)
-    const branchLog = await git.log(`${base}..${branch}`, root)
+    const branchLog = await git.commitLog(`${base}..${branch}`, root)
     const branchDiffStat = await git.diffStat(`${base}..${branch}`, root)
 
     for (const file of conflicts) {
       spin.text = `Resolving ${file}`
 
-      const oursDiff = await git.fileDiff(base, "HEAD", file, root)
+      const [oursDiff, theirsDiff] = await Promise.all([
-      const theirsDiff = await git.fileDiff(base, branch, file, root)
+        git.fileDiff(base, "HEAD", file, root),
+        git.fileDiff(base, branch, file, root),
+      ])
       const content = await Bun.file(join(root, file)).text()
 
       const context = [
@@ -48,19 +56,19 @@ export async function action(branch: string) {
         `Merging branch \`${branch}\` into \`${current}\``,
         ``,
         `### Commits on \`${branch}\`:`,
-        branchLog || "(no commits)",
+        (branchLog && truncate(branchLog, 50)) || "(no commits)",
         ``,
         `### Overall changes on \`${branch}\`:`,
-        branchDiffStat || "(no changes)",
+        (branchDiffStat && truncate(branchDiffStat, 100)) || "(no changes)",
         ``,
         `---`,
         `## Conflicted File: ${file}`,
         ``,
         `### Changes made on current branch (\`${current}\`):`,
-        oursDiff || "(no changes to this file)",
+        (oursDiff && truncate(oursDiff)) || "(no changes to this file)",
         ``,
         `### Changes made on incoming branch (\`${branch}\`):`,
-        theirsDiff || "(no changes to this file)",
+        (theirsDiff && truncate(theirsDiff)) || "(no changes to this file)",
         ``,
         `### File with conflict markers:`,
         content,

src/git.ts

@@ -136,20 +136,29 @@ export async function mergeBase(ref1: string, ref2: string, cwd: string): Promis
 }
 
 /** Get a one-line-per-commit log for a revision range. */
-export async function log(range: string, cwd: string): Promise<string> {
+export async function commitLog(range: string, cwd: string): Promise<string> {
   const result = await $`git log --oneline ${range}`.cwd(cwd).nothrow().quiet()
+  if (result.exitCode !== 0) {
+    throw new Error(`Failed to get log for range "${range}"`)
+  }
   return result.text().trim()
 }
 
 /** Get a diff stat summary for a revision range. */
 export async function diffStat(range: string, cwd: string): Promise<string> {
   const result = await $`git diff --stat ${range}`.cwd(cwd).nothrow().quiet()
+  if (result.exitCode !== 0) {
+    throw new Error(`Failed to get diff stat for range "${range}"`)
+  }
   return result.text().trim()
 }
 
 /** Get the diff for a specific file between two refs. */
 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}"`)
+  }
   return result.text().trim()
 }