fix(app): stabilize virtual session timeline interactions (#28422)

packages/ui/src/components/session-diff.ts

@@ -1,5 +1,5 @@
 import { parseDiffFromFile, parsePatchFiles, type FileDiffMetadata } from "@pierre/diffs"
-import { formatPatch, parsePatch, structuredPatch } from "diff"
+import { parsePatch } from "diff"
 import type { SnapshotFileDiff, VcsFileDiff } from "@opencode-ai/sdk/v2"
 
 type LegacyDiff = {
@@ -14,107 +14,35 @@ type LegacyDiff = {
 
 type SnapshotDiff = SnapshotFileDiff & { file: string }
 type ReviewDiff = SnapshotDiff | VcsFileDiff | LegacyDiff
+export type DiffSource = Pick<LegacyDiff, "file" | "patch" | "before" | "after">
 
 export type ViewDiff = {
   file: string
-  patch: string
   additions: number
   deletions: number
   status?: "added" | "deleted" | "modified"
   fileDiff: FileDiffMetadata
 }
 
-const cache = new Map<string, FileDiffMetadata>()
+const diffCacheLimit = 16
+const patchFileDiffCache = new Map<string, FileDiffMetadata>()
 
-function patch(diff: ReviewDiff) {
-  if (typeof diff.patch === "string") {
-    try {
-      const [patch] = parsePatch(diff.patch)
-      const beforeLines: Array<{ text: string; newline: boolean }> = []
-      const afterLines: Array<{ text: string; newline: boolean }> = []
-      let previous: "-" | "+" | " " | undefined
-
-      const patchIsPartial = patch.hunks.every((h) => h.oldStart > 1)
-
-      for (const hunk of patch.hunks) {
-        for (const line of hunk.lines) {
-          if (line.startsWith("\\")) {
-            if (previous === "-" || previous === " ") {
-              const before = beforeLines.at(-1)
-              if (before) before.newline = false
-            }
-            if (previous === "+" || previous === " ") {
-              const after = afterLines.at(-1)
-              if (after) after.newline = false
-            }
-            continue
-          }
-
-          if (line.startsWith("-")) {
-            beforeLines.push({ text: line.slice(1), newline: true })
-            previous = "-"
-          } else if (line.startsWith("+")) {
-            afterLines.push({ text: line.slice(1), newline: true })
-            previous = "+"
-          } else {
-            // context line (starts with ' ')
-            beforeLines.push({ text: line.slice(1), newline: true })
-            afterLines.push({ text: line.slice(1), newline: true })
-            previous = " "
-          }
-        }
-      }
-
-      return {
-        before: beforeLines.map((line) => line.text + (line.newline ? "\n" : "")).join(""),
-        after: afterLines.map((line) => line.text + (line.newline ? "\n" : "")).join(""),
-        patch: diff.patch,
-        patchIsPartial,
-      }
-    } catch {
-      return { before: "", after: "", patch: diff.patch, patchIsPartial: false }
-    }
-  }
-  return {
-    before: "before" in diff && typeof diff.before === "string" ? diff.before : "",
-    after: "after" in diff && typeof diff.after === "string" ? diff.after : "",
-    patch: formatPatch(
-      structuredPatch(
-        diff.file,
-        diff.file,
-        "before" in diff && typeof diff.before === "string" ? diff.before : "",
-        "after" in diff && typeof diff.after === "string" ? diff.after : "",
-        "",
-        "",
-        { context: Number.MAX_SAFE_INTEGER },
-      ),
-    ),
-    patchIsPartial: false,
-  }
-}
-
-function file(file: string, patch: string, before: string, after: string, partial = false) {
-  const hit = cache.get(patch)
-  if (hit) return hit
-
-  let value: FileDiffMetadata | undefined
-  if (partial) value = parsePatchFiles(patch)[0]?.files[0]
-  if (value === undefined) value = parseDiffFromFile({ name: file, contents: before }, { name: file, contents: after })
-
-  cache.set(patch, value)
-  return value
+export function resolveFileDiff(diff: DiffSource) {
+  if (typeof diff.patch === "string") return fileDiffFromPatch(diff.file, diff.patch)
+  return fileDiffFromContent(
+    diff.file,
+    typeof diff.before === "string" ? diff.before : "",
+    typeof diff.after === "string" ? diff.after : "",
+  )
 }
 
 export function normalize(diff: ReviewDiff): ViewDiff {
-  const next = patch(diff)
-  const fileDiff = file(diff.file, next.patch, next.before, next.after, next.patchIsPartial)
   return {
     file: diff.file,
-    patch: next.patch,
     additions: diff.additions,
     deletions: diff.deletions,
     status: diff.status,
-    fileDiff,
+    fileDiff: resolveFileDiff(diff),
   }
 }
 
@@ -122,3 +50,40 @@ export function text(diff: ViewDiff, side: "deletions" | "additions") {
   if (side === "deletions") return diff.fileDiff.deletionLines.join("")
   return diff.fileDiff.additionLines.join("")
 }
+
+function fileDiffFromPatch(file: string, patch: string) {
+  const key = `${file}\0${patch}`
+  const hit = patchFileDiffCache.get(key)
+  if (hit) {
+    patchFileDiffCache.delete(key)
+    patchFileDiffCache.set(key, hit)
+    return hit
+  }
+
+  const input = patchInput(file, patch)
+  const value = (input ? parsePatchFiles(input)[0]?.files[0] : undefined) ?? emptyFileDiff(file)
+  patchFileDiffCache.set(key, value)
+  while (patchFileDiffCache.size > diffCacheLimit) patchFileDiffCache.delete(patchFileDiffCache.keys().next().value!)
+  return value
+}
+
+function patchInput(file: string, patch: string) {
+  try {
+    const parsed = parsePatch(patch)[0]
+    if (!parsed) return
+    if (parsed.index || parsed.oldFileName || parsed.newFileName) return patch
+    if (!parsed.hunks.length) return
+    return `Index: ${file}\n===================================================================\n--- ${file}\t\n+++ ${file}\t\n${patch}`
+  } catch {
+    return
+  }
+}
+
+function fileDiffFromContent(file: string, before: string, after: string) {
+  if (!before && !after) return emptyFileDiff(file)
+  return parseDiffFromFile({ name: file, contents: before }, { name: file, contents: after })
+}
+
+function emptyFileDiff(file: string) {
+  return parseDiffFromFile({ name: file, contents: "" }, { name: file, contents: "" })
+}