core: preserve upstream Myers diff code to keep upstream merges clean

The previous commit deleted ~150 lines of upstream OpenCode diff code because the git-based path always runs first. Restoring those lines as dead code (behind an early-return kilocode_change block) keeps our diff from upstream minimal, so future OpenCode syncs to the hot diffFull code path don't conflict. No runtime behavior change — the git-based DiffFull path still short-circuits before the restored Myers loop executes.

Author: alex-alecu

packages/opencode/src/file/index.ts

@@ -5,6 +5,7 @@ import { AppFileSystem } from "@/filesystem"
 import { Git } from "@/git"
 import { Effect, Layer, Context } from "effect"
 import * as Stream from "effect/Stream"
+import { formatPatch, structuredPatch } from "diff"
 import { DiffFull } from "@/kilocode/snapshot/diff-full" // kilocode_change
 import fuzzysort from "fuzzysort"
 import ignore from "ignore"
@@ -559,10 +560,19 @@ export namespace File {
             diff = yield* gitText(["-c", "core.fsmonitor=false", "diff", "--staged", "--", file])
           }
           if (diff.trim()) {
-            // kilocode_change start — patch via git, never the JS Myers implementation
+            // kilocode_change start — patch via git (DiffFull.file) instead of the JS Myers
+            // implementation. Upstream structuredPatch branch below is kept as dead code so
+            // our diff from upstream stays minimal and future merges don't conflict.
             const got = yield* DiffFull.file(gitText, file)
             if (got) return { type: "text" as const, content, patch: got.patch, diff: got.text }
+            return { type: "text" as const, content }
             // kilocode_change end
+            const original = yield* git.show(Instance.directory, "HEAD", file)
+            const patch = structuredPatch(file, file, original, content, "old", "new", {
+              context: Infinity,
+              ignoreWhitespace: true,
+            })
+            return { type: "text" as const, content, patch, diff: formatPatch(patch) }
           }
           return { type: "text" as const, content }
         }

packages/opencode/src/snapshot/index.ts

@@ -1,5 +1,6 @@
 import { Cause, Duration, Effect, Layer, Schedule, Semaphore, Context, Stream } from "effect"
 import { ChildProcess, ChildProcessSpawner } from "effect/unstable/process"
+import { formatPatch, structuredPatch } from "diff"
 import path from "path"
 import z from "zod"
 import { makeRuntime } from "@/effect/run-service" // kilocode_change
@@ -525,6 +526,144 @@ export namespace Snapshot {
           const diffFull = Effect.fnUntraced(function* (from: string, to: string) {
             return yield* locked(
               Effect.gen(function* () {
+                type Row = {
+                  file: string
+                  status: "added" | "deleted" | "modified"
+                  binary: boolean
+                  additions: number
+                  deletions: number
+                }
+
+                type Ref = {
+                  file: string
+                  side: "before" | "after"
+                  ref: string
+                }
+
+                const show = Effect.fnUntraced(function* (row: Row) {
+                  if (row.binary) return ["", ""]
+                  if (row.status === "added") {
+                    return [
+                      "",
+                      yield* git([...cfg, ...args(["show", `${to}:${row.file}`])]).pipe(
+                        Effect.map((item) => item.text),
+                      ),
+                    ]
+                  }
+                  if (row.status === "deleted") {
+                    return [
+                      yield* git([...cfg, ...args(["show", `${from}:${row.file}`])]).pipe(
+                        Effect.map((item) => item.text),
+                      ),
+                      "",
+                    ]
+                  }
+                  return yield* Effect.all(
+                    [
+                      git([...cfg, ...args(["show", `${from}:${row.file}`])]).pipe(Effect.map((item) => item.text)),
+                      git([...cfg, ...args(["show", `${to}:${row.file}`])]).pipe(Effect.map((item) => item.text)),
+                    ],
+                    { concurrency: 2 },
+                  )
+                })
+
+                const load = Effect.fnUntraced(
+                  function* (rows: Row[]) {
+                    const refs = rows.flatMap((row) => {
+                      if (row.binary) return []
+                      if (row.status === "added")
+                        return [{ file: row.file, side: "after", ref: `${to}:${row.file}` } satisfies Ref]
+                      if (row.status === "deleted") {
+                        return [{ file: row.file, side: "before", ref: `${from}:${row.file}` } satisfies Ref]
+                      }
+                      return [
+                        { file: row.file, side: "before", ref: `${from}:${row.file}` } satisfies Ref,
+                        { file: row.file, side: "after", ref: `${to}:${row.file}` } satisfies Ref,
+                      ]
+                    })
+                    if (!refs.length) return new Map<string, { before: string; after: string }>()
+
+                    const proc = ChildProcess.make("git", [...cfg, ...args(["cat-file", "--batch"])], {
+                      cwd: state.directory,
+                      extendEnv: true,
+                      stdin: Stream.make(new TextEncoder().encode(refs.map((item) => item.ref).join("\n") + "\n")),
+                    })
+                    const handle = yield* spawner.spawn(proc)
+                    const [out, err] = yield* Effect.all(
+                      [Stream.mkUint8Array(handle.stdout), Stream.mkString(Stream.decodeText(handle.stderr))],
+                      { concurrency: 2 },
+                    )
+                    const code = yield* handle.exitCode
+                    if (code !== 0) {
+                      log.info("git cat-file --batch failed during snapshot diff, falling back to per-file git show", {
+                        stderr: err,
+                        refs: refs.length,
+                      })
+                      return
+                    }
+
+                    const fail = (msg: string, extra?: Record<string, string>) => {
+                      log.info(msg, { ...extra, refs: refs.length })
+                      return undefined
+                    }
+
+                    const map = new Map<string, { before: string; after: string }>()
+                    const dec = new TextDecoder()
+                    let i = 0
+                    for (const ref of refs) {
+                      let end = i
+                      while (end < out.length && out[end] !== 10) end += 1
+                      if (end >= out.length) {
+                        return fail(
+                          "git cat-file --batch returned a truncated header during snapshot diff, falling back to per-file git show",
+                        )
+                      }
+
+                      const head = dec.decode(out.slice(i, end))
+                      i = end + 1
+                      const hit = map.get(ref.file) ?? { before: "", after: "" }
+                      if (head.endsWith(" missing")) {
+                        map.set(ref.file, hit)
+                        continue
+                      }
+
+                      const match = head.match(/^[0-9a-f]+ blob (\d+)$/)
+                      if (!match) {
+                        return fail(
+                          "git cat-file --batch returned an unexpected header during snapshot diff, falling back to per-file git show",
+                          { head },
+                        )
+                      }
+
+                      const size = Number(match[1])
+                      if (!Number.isInteger(size) || size < 0 || i + size >= out.length || out[i + size] !== 10) {
+                        return fail(
+                          "git cat-file --batch returned truncated content during snapshot diff, falling back to per-file git show",
+                          { head },
+                        )
+                      }
+
+                      const text = dec.decode(out.slice(i, i + size))
+                      if (ref.side === "before") hit.before = text
+                      if (ref.side === "after") hit.after = text
+                      map.set(ref.file, hit)
+                      i += size + 1
+                    }
+
+                    if (i !== out.length) {
+                      return fail(
+                        "git cat-file --batch returned trailing data during snapshot diff, falling back to per-file git show",
+                      )
+                    }
+
+                    return map
+                  },
+                  Effect.scoped,
+                  Effect.catch(() =>
+                    Effect.succeed<Map<string, { before: string; after: string }> | undefined>(undefined),
+                  ),
+                )
+
                 const result: Snapshot.FileDiff[] = []
                 const status = new Map<string, "added" | "deleted" | "modified">()
 
@@ -564,7 +703,7 @@ export namespace Snapshot {
                         binary,
                         additions: Number.isFinite(additions) ? additions : 0,
                         deletions: Number.isFinite(deletions) ? deletions : 0,
-                      },
+                      } satisfies Row,
                     ]
                   })
 
@@ -577,9 +716,14 @@ export namespace Snapshot {
                 }
 
                 const step = 100
+                const patch = (file: string, before: string, after: string) =>
+                  formatPatch(structuredPatch(file, file, before, after, "", "", { context: Number.MAX_SAFE_INTEGER }))
+
+                // kilocode_change start — route patches through git (DiffFull.batch) instead of the
+                // JS Myers implementation. Upstream Myers loop below is kept as dead code so our
+                // diff from upstream stays minimal and future merges don't conflict.
                 for (let i = 0; i < rows.length; i += step) {
                   const run = rows.slice(i, i + step)
-                  // kilocode_change start — bulk-load patches from `git diff`; no JS Myers fallback
                   const patches = yield* DiffFull.batch(
                     (cmd) => git([...quote, ...args(cmd)], { cwd: state.directory }),
                     from,
@@ -595,7 +739,25 @@ export namespace Snapshot {
                       status: row.status,
                     })
                   }
-                  // kilocode_change end
+                }
+                return result
+                // kilocode_change end
+
+                for (let i = 0; i < rows.length; i += step) {
+                  const run = rows.slice(i, i + step)
+                  const text = yield* load(run)
+
+                  for (const row of run) {
+                    const hit = text?.get(row.file) ?? { before: "", after: "" }
+                    const [before, after] = row.binary ? ["", ""] : text ? [hit.before, hit.after] : yield* show(row)
+                    result.push({
+                      file: row.file,
+                      patch: row.binary ? "" : patch(row.file, before, after),
+                      additions: row.additions,
+                      deletions: row.deletions,
+                      status: row.status,
+                    })
+                  }
                 }
 
                 return result