fix(maestro): render accurate diffs

web/src/structuredDiff.test.ts

@@ -42,6 +42,42 @@ describe("computeDiffLines", () => {
     ]);
   });
 
+  it("handles an insertion without changing surrounding lines", () => {
+    expect(texts(computeDiffLines("a\nc\n", "a\nb\nc\n"))).toEqual([
+      ["ctx", "a"],
+      ["add", "b"],
+      ["ctx", "c"],
+    ]);
+  });
+
+  it("handles a deletion without changing surrounding lines", () => {
+    expect(texts(computeDiffLines("a\nb\nc\n", "a\nc\n"))).toEqual([
+      ["ctx", "a"],
+      ["del", "b"],
+      ["ctx", "c"],
+    ]);
+  });
+
+  it("renders two empty files without invented lines", () => {
+    expect(computeDiffLines("", "")).toEqual([]);
+  });
+
+  it("shows when a final newline is added", () => {
+    expect(texts(computeDiffLines("a", "a\n"))).toEqual([
+      ["del", "a"],
+      ["eof", "\\ No newline at end of file"],
+      ["add", "a"],
+    ]);
+  });
+
+  it("shows when a final newline is removed", () => {
+    expect(texts(computeDiffLines("a\n", "a"))).toEqual([
+      ["del", "a"],
+      ["add", "a"],
+      ["eof", "\\ No newline at end of file"],
+    ]);
+  });
+
   it("collapses a long unchanged interior run, keeping 3 lines of context each side", () => {
     const common = Array.from({ length: 20 }, (_, i) => `line${i}`);
     const oldText = [...common.slice(0, 10), "OLD", ...common.slice(10)].join("\n");
@@ -85,10 +121,22 @@ describe("computeDiffLines", () => {
     const lines = computeDiffLines("a\nb", "a\nb\nc");
     expect(texts(lines)).toEqual([
       ["ctx", "a"],
-      ["ctx", "b"],
+      ["del", "b"],
+      ["eof", "\\ No newline at end of file"],
+      ["add", "b"],
       ["add", "c"],
+      ["eof", "\\ No newline at end of file"],
     ]);
   });
+
+  it("falls back to a bounded coarse diff for a pathological changed middle", () => {
+    const oldLines = Array.from({ length: 501 }, (_, index) => `line${index}`);
+    const newLines = [...oldLines.slice(1), oldLines[0]];
+    const lines = computeDiffLines(`${oldLines.join("\n")}\n`, `${newLines.join("\n")}\n`);
+    expect(lines).toHaveLength(1_002);
+    expect(lines.slice(0, 501).every((line) => line.kind === "del")).toBe(true);
+    expect(lines.slice(501).every((line) => line.kind === "add")).toBe(true);
+  });
 });
 
 describe("diffStats", () => {