improve ux when errors are logged during startup, fix #5935 (#6020)

mitmproxy/addons/errorcheck.py

@@ -8,8 +8,14 @@ from mitmproxy import log
 class ErrorCheck:
     """Monitor startup for error log entries, and terminate immediately if there are some."""
 
-    def __init__(self, log_to_stderr: bool = False) -> None:
-        self.log_to_stderr = log_to_stderr
+    repeat_errors_on_stderr: bool
+    """
+    Repeat all errors on stderr before exiting.
+    This is useful for the console UI, which otherwise swallows all output.
+    """
+
+    def __init__(self, repeat_errors_on_stderr: bool = False) -> None:
+        self.repeat_errors_on_stderr = repeat_errors_on_stderr
 
         self.logger = ErrorCheckHandler()
         self.logger.install()
@@ -21,10 +27,14 @@ class ErrorCheck:
         # don't run immediately, wait for all logging tasks to finish.
         await asyncio.sleep(0)
         if self.logger.has_errored:
-            if self.log_to_stderr:
-                plural = "s" if len(self.logger.has_errored) > 1 else ""
+            plural = "s" if len(self.logger.has_errored) > 1 else ""
+            if self.repeat_errors_on_stderr:
                 msg = "\n".join(r.msg for r in self.logger.has_errored)
-                print(f"Error{plural} on startup: {msg}", file=sys.stderr)
+                print(f"Error{plural} logged during startup: {msg}", file=sys.stderr)
+            else:
+                print(
+                    f"Error{plural} logged during startup, exiting...", file=sys.stderr
+                )
 
             sys.exit(1)
 

mitmproxy/tools/console/master.py

@@ -55,7 +55,7 @@ class ConsoleMaster(master.Master):
             readfile.ReadFile(),
             consoleaddons.ConsoleAddon(self),
             keymap.KeymapConfig(self),
-            errorcheck.ErrorCheck(log_to_stderr=True),
+            errorcheck.ErrorCheck(repeat_errors_on_stderr=True),
         )
 
         self.window: window.Window | None = None

test/mitmproxy/addons/test_errorcheck.py

@@ -1,3 +1,5 @@
+import logging
+
 import pytest
 
 from mitmproxy.addons.errorcheck import ErrorCheck
@@ -13,10 +15,19 @@ def test_errorcheck(tdata, capsys):
                 tdata.path("mitmproxy/data/addonscripts/load_error.py"),
             ]
         )
-    assert "Error on startup" in capsys.readouterr().err
+    assert "Error logged during startup" in capsys.readouterr().err
 
 
 async def test_no_error():
     e = ErrorCheck()
     await e.shutdown_if_errored()
     e.finish()
+
+
+async def test_error_message(capsys):
+    e = ErrorCheck()
+    logging.error("wat")
+    logging.error("wat")
+    with pytest.raises(SystemExit):
+        await e.shutdown_if_errored()
+    assert "Errors logged during startup" in capsys.readouterr().err