Respect JSON output mode for syntax errors (#21386)

Fixes #21370.

A

---------

Co-authored-by: Adam Turner <turner@hudson-trading.com>

Author: AA-Turner

mypy/build.py

@@ -493,7 +493,12 @@ def build_inner(
 
     source_set = BuildSourceSet(sources)
     cached_read = fscache.read
-    errors = Errors(options, read_source=lambda path: read_py_file(path, cached_read))
+    error_formatter = None if options.output is None else OUTPUT_CHOICES.get(options.output)
+    errors = Errors(
+        options,
+        read_source=lambda path: read_py_file(path, cached_read),
+        error_formatter=error_formatter,
+    )
     # Record import errors so that they can be replayed by the workers.
     if workers:
         errors.global_watcher = True
@@ -516,7 +521,7 @@ def build_inner(
         plugin=plugin,
         plugins_snapshot=snapshot,
         errors=errors,
-        error_formatter=None if options.output is None else OUTPUT_CHOICES.get(options.output),
+        error_formatter=error_formatter,
         flush_errors=flush_errors,
         fscache=fscache,
         stdout=stdout,

mypy/errors.py

@@ -500,13 +500,15 @@ def __init__(
         *,
         read_source: Callable[[str], list[str] | None] | None = None,
         hide_error_codes: bool | None = None,
+        error_formatter: ErrorFormatter | None = None,
     ) -> None:
         self.options = options
         self.hide_error_codes = (
             hide_error_codes if hide_error_codes is not None else options.hide_error_codes
         )
         # We use fscache to read source code when showing snippets.
         self.read_source = read_source
+        self.error_formatter = error_formatter
         self.initialize()
 
     def initialize(self) -> None:
@@ -1129,7 +1131,9 @@ def new_messages(self) -> list[str]:
         for path in self.error_info_map.keys():
             if path not in self.flushed_files:
                 error_tuples = self.file_messages(path)
-                msgs.extend(self.format_messages(path, error_tuples))
+                msgs.extend(
+                    self.format_messages(path, error_tuples, formatter=self.error_formatter)
+                )
         return msgs
 
     def targets(self) -> set[str]:

test-data/unit/outputjson.test

@@ -42,3 +42,10 @@ bar('42')
 {"file": "main", "line": 12, "column": 12, "end_line": 12, "end_column": 15, "message": "Revealed type is \"Overload(def (), def (x: int))\"", "hint": null, "code": "misc", "severity": "note"}
 {"file": "main", "line": 14, "column": 0, "end_line": 14, "end_column": 9, "message": "No overload variant of \"foo\" matches argument type \"str\"", "hint": "Possible overload variants:\n    def foo() -> None\n    def foo(x: int) -> None", "code": "call-overload", "severity": "error"}
 {"file": "main", "line": 17, "column": 0, "end_line": 17, "end_column": 9, "message": "Too many arguments for \"bar\"", "hint": null, "code": "call-arg", "severity": "error"}
+
+[case testOutputJsonSyntaxError]
+# flags: --output=json
+klass foo
+[out]
+{"file": "main", "line": 2, "column": 7, "end_line": 2, "end_column": 8, "message": "Invalid syntax", "hint": null, "code": "syntax", "severity": "error"}
+!!! Mypy crashed !!!