fix(core): rename instead of deleting when a patch only changes a file's case

packages/core/src/tool/plugin/patch.ts

@@ -207,15 +207,36 @@ export const Plugin = {
                   Effect.gen(function* () {
                     const moveTarget = change.type === "update" ? change.moveTarget : undefined
                     const target = moveTarget ?? change.target
+                    // On macOS and Windows a move that only changes case targets the same file, so the new name already
+                    // exists, and writing it then removing the old one would delete the file. Such a move writes in
+                    // place and renames. Symlinks keep the write-and-remove path, which leaves their target alone.
+                    const recased =
+                      moveTarget !== undefined &&
+                      moveTarget.absolute.toLowerCase() === change.target.absolute.toLowerCase() &&
+                      (yield* environment.files.stat(change.target.absolute).pipe(
+                        Effect.map((info) => info.type === "file"),
+                        Effect.orElseSucceed(() => false),
+                      )) &&
+                      (yield* environment.files.stat(moveTarget.absolute).pipe(
+                        Effect.as(true),
+                        Effect.orElseSucceed(() => false),
+                      ))
                     if (change.type === "delete")
                       yield* environment.files
                         .remove(change.target.absolute)
                         .pipe(Effect.mapError((error) => fail(`Failed to delete ${change.target.resource}`, error)))
                     if (change.type !== "delete")
                       yield* environment.files
-                        .write(target.absolute, new TextEncoder().encode(change.content))
+                        .write(
+                          recased ? change.target.absolute : target.absolute,
+                          new TextEncoder().encode(change.content),
+                        )
                         .pipe(Effect.mapError((error) => fail(`Failed to write ${target.resource}`, error)))
-                    if (moveTarget)
+                    if (moveTarget && recased)
+                      yield* environment.files
+                        .move(change.target.absolute, moveTarget.absolute)
+                        .pipe(Effect.mapError((error) => fail(`Failed to rename ${change.target.resource}`, error)))
+                    if (moveTarget && !recased)
                       yield* environment.files
                         .remove(change.target.absolute)
                         .pipe(

packages/core/test/tool-patch.test.ts

@@ -457,6 +457,40 @@ describe("PatchTool", () => {
     ),
   )
 
+  it.live("renames a file when the move only changes its case", () =>
+    withTempTool((directory, registry) =>
+      Effect.gen(function* () {
+        yield* Effect.promise(() => fs.writeFile(path.join(directory, "same.txt"), "before\n"))
+        expect(
+          yield* executeTool(
+            registry,
+            call("*** Begin Patch\n*** Update File: same.txt\n*** Move to: Same.txt\n@@\n-before\n+after\n*** End Patch"),
+          ),
+        ).toMatchObject({ status: "completed" })
+        expect(yield* Effect.promise(() => fs.readdir(directory))).toEqual(["Same.txt"])
+        expect(yield* Effect.promise(() => fs.readFile(path.join(directory, "Same.txt"), "utf8"))).toBe("after\n")
+      }),
+    ),
+  )
+
+  it.live("moves into a directory whose name differs only in case", () =>
+    withTempTool((directory, registry) =>
+      Effect.gen(function* () {
+        yield* Effect.promise(async () => {
+          await fs.mkdir(path.join(directory, "Foo"))
+          await fs.writeFile(path.join(directory, "Foo", "a.txt"), "before\n")
+        })
+        expect(
+          yield* executeTool(
+            registry,
+            call("*** Begin Patch\n*** Update File: Foo/a.txt\n*** Move to: foo/a.txt\n@@\n-before\n+after\n*** End Patch"),
+          ),
+        ).toMatchObject({ status: "completed" })
+        expect(yield* Effect.promise(() => fs.readFile(path.join(directory, "foo", "a.txt"), "utf8"))).toBe("after\n")
+      }),
+    ),
+  )
+
   it.live("moves a symlink without deleting its target", () =>
     withTempTool((directory, registry) =>
       Effect.gen(function* () {