Propagate exceptions from run_installer()

This change catches exceptions derived from Exception and
KeyboardInterrupt raised by `installer`, while run by multiple
processes, and propagates them back to earlier stack entries. This will
prevent any OSError and BrokenPipe exceptions that would otherwise be
raised when one process has an exception while the other processes are
still running.

This also handles the MemoryError exception we saw in #416, and offers
some suggestions for solving the issue.

tests/test_install.py

@@ -16,6 +16,7 @@ from pytest_socket import disable_socket
 
 from aqt.archives import QtPackage
 from aqt.exceptions import ArchiveDownloadError, ArchiveExtractionError
+from aqt.helper import Settings
 from aqt.installer import Cli, installer
 
 
@@ -536,9 +537,44 @@ def test_install_nonexistent_archives(monkeypatch, capsys, cmd, xml_file: Option
     assert actual == expected, "{0} != {1}".format(actual, expected)
 
 
-def test_install_keyboard_interrupt(monkeypatch, capsys):
-    def mock_keyboard_interrupt(*args):
-        raise KeyboardInterrupt()
+@pytest.mark.parametrize(
+    "make_exception, expect_end_msg, settings_file",
+    (
+        (
+            "RuntimeError()",
+            "===========================PLEASE FILE A BUG REPORT===========================\n"
+            "You have discovered a bug in aqt.\n"
+            "Please file a bug report at https://github.com/miurahr/aqtinstall/issues.\n"
+            "Please remember to include a copy of this program's output in your report.",
+            "../aqt/settings.ini",
+        ),
+        (
+            "KeyboardInterrupt()",
+            "Caught KeyboardInterrupt, terminating installer workers\n" "Installer halted by keyboard interrupt.",
+            "../aqt/settings.ini",
+        ),
+        (
+            "MemoryError()",
+            "Caught MemoryError, terminating installer workers\n"
+            "Out of memory when downloading and extracting archives in parallel.\n"
+            "==============================Suggested follow-up:==============================\n"
+            "* Please reduce your 'concurrency' setting (see "
+            "https://aqtinstall.readthedocs.io/en/stable/configuration.html#configuration)",
+            "../aqt/settings.ini",
+        ),
+        (
+            "MemoryError()",
+            "Caught MemoryError, terminating installer workers\n"
+            "Out of memory when downloading and extracting archives.\n"
+            "==============================Suggested follow-up:==============================\n"
+            "* Please free up more memory.",
+            "data/settings_no_concurrency.ini",
+        ),
+    ),
+)
+def test_install_pool_exception(monkeypatch, capsys, make_exception, expect_end_msg, settings_file):
+    def mock_installer_func(*args):
+        raise eval(make_exception)
 
     host, target, ver, arch = "windows", "desktop", "6.1.0", "win64_mingw81"
     updates_url = "windows_x86/desktop/qt6_610/Updates.xml"
@@ -548,15 +584,13 @@ def test_install_keyboard_interrupt(monkeypatch, capsys):
     mock_get_url, mock_download_archive = make_mock_geturl_download_archive(archives, arch, host, updates_url)
     monkeypatch.setattr("aqt.archives.getUrl", mock_get_url)
     monkeypatch.setattr("aqt.installer.getUrl", mock_get_url)
-    monkeypatch.setattr("aqt.installer.installer", mock_keyboard_interrupt)
+    monkeypatch.setattr("aqt.installer.installer", mock_installer_func)
 
+    Settings.load_settings(str(Path(__file__).parent / settings_file))
     cli = Cli()
-    cli._setup_settings()
     assert cli.run(cmd) == 1
     out, err = capsys.readouterr()
-    assert err.rstrip().endswith(
-        "Caught KeyboardInterrupt, terminating installer workers\nInstaller halted by keyboard interrupt."
-    )
+    assert err.rstrip().endswith(expect_end_msg)
 
 
 def test_install_installer_archive_extraction_err(monkeypatch):