Don't delete fine-grained deps cache when a module has an error

mypy/build.py

@@ -1315,13 +1315,16 @@ def delete_cache(id: str, path: str, manager: BuildManager) -> None:
     see #4043 for an example.
     """
     path = manager.normpath(path)
-    cache_paths = get_cache_names(id, path, manager)
+    # We don't delete .deps files on errors, since the dependencies
+    # are mostly generated from other files and the metadata is
+    # tracked separately.
+    meta_path, data_path, _ = get_cache_names(id, path, manager)
+    cache_paths = [meta_path, data_path]
     manager.log('Deleting {} {} {}'.format(id, path, " ".join(x for x in cache_paths if x)))
 
     for filename in cache_paths:
         try:
-            if filename:
-                manager.metastore.remove(filename)
+            manager.metastore.remove(filename)
         except OSError as e:
             if e.errno != errno.ENOENT:
                 manager.log("Error deleting cache file {}: {}".format(filename, e.strerror))

test-data/unit/check-incremental.test

@@ -3630,6 +3630,19 @@ def foo() -> None:
 [out2]
 tmp/main.py:2: error: "int" has no attribute "foo"
 
+[case testIncrementalFineGrainedCacheError1]
+# flags: --cache-fine-grained --no-sqlite-cache
+import a
+[file a.py]
+[file b.py]
+x = 0
+[file a.py.2]
+from b import x
+1 + 'lol'
+[out]
+[out2]
+tmp/a.py:2: error: Unsupported operand types for + ("int" and "str")
+
 [case testIncrementalBustedFineGrainedCache1]
 # flags: --cache-fine-grained --no-sqlite-cache
 import a