fix(ui): render whole-file patches as complete diffs (#30516)

packages/ui/src/components/apply-patch-file.test.ts

@@ -18,6 +18,7 @@ describe("apply patch file", () => {
 
     expect(file).toBeDefined()
     expect(file?.view.fileDiff.name).toBe("a.ts")
+    expect(file?.view.fileDiff.isPartial).toBe(false)
     expect(text(file!.view, "deletions")).toBe("one\ntwo\n")
     expect(text(file!.view, "additions")).toBe("one\nthree\n")
   })

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

@@ -2,7 +2,7 @@ import { describe, expect, test } from "bun:test"
 import { normalize, resolveFileDiff, text } from "./session-diff"
 
 describe("session diff", () => {
-  test("keeps unified patch content", () => {
+  test("renders whole-file unified patches as complete diffs", () => {
     const diff = {
       file: "a.ts",
       patch:
@@ -14,7 +14,7 @@ describe("session diff", () => {
     const view = normalize(diff)
 
     expect(view.fileDiff.name).toBe("a.ts")
-    expect(view.fileDiff.isPartial).toBe(true)
+    expect(view.fileDiff.isPartial).toBe(false)
     expect(text(view, "deletions")).toBe("one\ntwo\n")
     expect(text(view, "additions")).toBe("one\nthree\n")
   })
@@ -34,6 +34,26 @@ describe("session diff", () => {
     expect(text(view, "additions")).toBe("one\nthree")
   })
 
+  test("renders whole-file VCS patches as complete diffs", () => {
+    const fileDiff = resolveFileDiff({
+      file: "a.ts",
+      patch: "diff --git a/a.ts b/a.ts\nindex 1a2b3c4..5d6e7f8 100644\n--- a/a.ts\n+++ b/a.ts\n@@ -1,2 +1,2 @@\n one\n-old\n+new\n",
+    })
+
+    expect(fileDiff.isPartial).toBe(false)
+    expect(fileDiff.additionLines).toEqual(["one\n", "new\n"])
+  })
+
+  test("keeps ordinary leading tool patches partial", () => {
+    const fileDiff = resolveFileDiff({
+      file: "a.ts",
+      patch: "Index: a.ts\n===================================================================\n--- a.ts\n+++ a.ts\n@@ -1,5 +1,5 @@\n-old\n+new\n two\n three\n four\n five\n",
+    })
+
+    expect(fileDiff.isPartial).toBe(true)
+    expect(fileDiff.additionLines).toEqual(["new\n", "two\n", "three\n", "four\n", "five\n"])
+  })
+
   test("keeps separated patch hunks partial without complete file contents", () => {
     const fileDiff = resolveFileDiff({
       file: "project.ts",

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

@@ -60,13 +60,68 @@ function fileDiffFromPatch(file: string, patch: string) {
     return hit
   }
 
-  const input = patchInput(file, patch)
-  const value = (input ? parsePatchFiles(input)[0]?.files[0] : undefined) ?? emptyFileDiff(file)
+  const contents = completePatchContents(patch)
+  const input = contents ? undefined : patchInput(file, patch)
+  const value = contents
+    ? fileDiffFromContent(file, contents.before, contents.after)
+    : (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 completePatchContents(patch: string) {
+  try {
+    const parsed = parsePatch(patch)[0]
+    if (!parsed || (!parsed.index && !parsed.oldFileName && !parsed.newFileName)) return
+    // Snapshot and VCS producers request full context. Tool patches use jsdiff's shorter default context.
+    if (!patch.startsWith("diff --git ") && !/^--- [^\n]*\t\r?\n\+\+\+ [^\n]*\t(?:\r?\n|$)/m.test(patch)) return
+    // Full patches collapse into one leading hunk. Separated hunks omit ranges and must stay partial.
+    if (parsed.hunks.length !== 1) return
+
+    const hunk = parsed.hunks[0]
+    if (!hunk || hunk.oldStart > 1 || hunk.newStart > 1) return
+
+    const before: Array<{ text: string; newline: boolean }> = []
+    const after: Array<{ text: string; newline: boolean }> = []
+    let previous: "-" | "+" | " " | undefined
+
+    for (const line of hunk.lines) {
+      if (line.startsWith("\\")) {
+        if (previous === "-" || previous === " ") {
+          const value = before.at(-1)
+          if (value) value.newline = false
+        }
+        if (previous === "+" || previous === " ") {
+          const value = after.at(-1)
+          if (value) value.newline = false
+        }
+        continue
+      }
+      if (line.startsWith("-")) {
+        before.push({ text: line.slice(1), newline: true })
+        previous = "-"
+        continue
+      }
+      if (line.startsWith("+")) {
+        after.push({ text: line.slice(1), newline: true })
+        previous = "+"
+        continue
+      }
+      if (!line.startsWith(" ")) return
+      before.push({ text: line.slice(1), newline: true })
+      after.push({ text: line.slice(1), newline: true })
+      previous = " "
+    }
+
+    const text = (lines: Array<{ text: string; newline: boolean }>) =>
+      lines.map((line) => line.text + (line.newline ? "\n" : "")).join("")
+    return { before: text(before), after: text(after) }
+  } catch {
+    return
+  }
+}
+
 function patchInput(file: string, patch: string) {
   try {
     const parsed = parsePatch(patch)[0]