From 0b621cb0ce2b54d3f93d8d41d8ff4257888a87e5 Mon Sep 17 00:00:00 2001
From: Florian Bruhin <me@the-compiler.org>
Date: Mon, 15 Mar 2021 20:23:24 +0100
Subject: Improve error messages for GUIProcess

---
 qutebrowser/misc/guiprocess.py       | 23 +++++++++++++++++++++--
 tests/end2end/features/spawn.feature |  2 +-
 tests/unit/misc/test_guiprocess.py   |  7 ++++++-
 3 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/qutebrowser/misc/guiprocess.py b/qutebrowser/misc/guiprocess.py
index 79c84c346..4aa3df55d 100644
--- a/qutebrowser/misc/guiprocess.py
+++ b/qutebrowser/misc/guiprocess.py
@@ -84,8 +84,27 @@ class GUIProcess(QObject):
         if error == QProcess.Crashed and not utils.is_windows:
             # Already handled via ExitStatus in _on_finished
             return
-        msg = self._proc.errorString()
-        message.error("Error while spawning {}: {}".format(self._what, msg))
+
+        what = f"{self._what} {self.cmd!r}"
+        error_descriptions = {
+            QProcess.FailedToStart: f"{what.capitalize()} failed to start",
+            QProcess.Crashed: f"{what.capitalize()} crashed",
+            QProcess.Timedout: f"{what.capitalize()} timed out",
+            QProcess.WriteError: f"Write error for {what}",
+            QProcess.WriteError: f"Read error for {what}",
+        }
+        error_string = self._proc.errorString()
+        msg = ': '.join([error_descriptions[error], error_string])
+
+        # We can't get some kind of error code from Qt...
+        # https://bugreports.qt.io/browse/QTBUG-44769
+        # However, it looks like those strings aren't actually translated?
+        known_errors = ['No such file or directory', 'Permission denied']
+        if (': ' in error_string and
+                error_string.split(': ', maxsplit=1)[1] in known_errors):
+            msg += f'\n(Hint: Make sure {self.cmd!r} exists and is executable)'
+
+        message.error(msg)
 
     @pyqtSlot(int, QProcess.ExitStatus)
     def _on_finished(self, code, status):
diff --git a/tests/end2end/features/spawn.feature b/tests/end2end/features/spawn.feature
index 11b344439..1c360893c 100644
--- a/tests/end2end/features/spawn.feature
+++ b/tests/end2end/features/spawn.feature
@@ -8,7 +8,7 @@ Feature: :spawn
 
     Scenario: Running :spawn with command that does not exist
         When I run :spawn command_does_not_exist127623
-        Then the error "Error while spawning command: *" should be shown
+        Then the error "Command 'command_does_not_exist127623' failed to start: *" should be shown
 
     Scenario: Starting a userscript which doesn't exist
         When I run :spawn -u this_does_not_exist
diff --git a/tests/unit/misc/test_guiprocess.py b/tests/unit/misc/test_guiprocess.py
index 9e1b3916c..18e926fab 100644
--- a/tests/unit/misc/test_guiprocess.py
+++ b/tests/unit/misc/test_guiprocess.py
@@ -226,7 +226,12 @@ def test_error(qtbot, proc, caplog, message_mock):
             proc.start('this_does_not_exist_either', [])
 
     msg = message_mock.getmsg(usertypes.MessageLevel.error)
-    assert msg.text.startswith("Error while spawning testprocess:")
+    assert msg.text.startswith(
+        "Testprocess 'this_does_not_exist_either' failed to start:")
+
+    if not utils.is_windows:
+        assert msg.text.endswith(
+            "(Hint: Make sure 'this_does_not_exist_either' exists and is executable)")
 
 
 def test_exit_unsuccessful(qtbot, proc, message_mock, py_proc, caplog):
-- 
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