feat(ci): improve error message on xml file not found (#757)

Author: jd

mergify_cli/ci/cli.py

@@ -9,6 +9,36 @@
 from mergify_cli.ci import upload
 
 
+class JUnitFile(click.Path):
+    """Custom Click parameter type for JUnit files with better error messages."""
+
+    def __init__(self) -> None:
+        super().__init__(exists=True, dir_okay=False)
+
+    def convert(  # type: ignore[override]
+        self,
+        value: str,
+        param: click.Parameter | None,
+        ctx: click.Context | None,
+    ) -> str:
+        try:
+            return super().convert(value, param, ctx)
+        except click.BadParameter as e:
+            if "does not exist" in str(e):
+                # Provide a more helpful error message
+                error_msg = (
+                    f"JUnit XML file '{value}' does not exist. \n\n"
+                    "This usually indicates that a previous CI step failed to generate the test results.\n"
+                    "Please check if your test execution step completed successfully and produced the expected output file."
+                )
+                raise click.BadParameter(
+                    error_msg,
+                    ctx=ctx,
+                    param=param,
+                ) from e
+            raise
+
+
 def _process_tests_target_branch(
     _ctx: click.Context,
     _param: click.Parameter,
@@ -68,7 +98,7 @@ def _process_tests_target_branch(
     "files",
     nargs=-1,
     required=True,
-    type=click.Path(exists=True, dir_okay=False),
+    type=JUnitFile(),
 )
 @utils.run_with_asyncio
 async def junit_upload(  # noqa: PLR0913
@@ -139,7 +169,7 @@ async def junit_upload(  # noqa: PLR0913
     "files",
     nargs=-1,
     required=True,
-    type=click.Path(exists=True, dir_okay=False),
+    type=JUnitFile(),
 )
 @utils.run_with_asyncio
 async def junit_process(  # noqa: PLR0913

mergify_cli/tests/ci/test_cli.py

@@ -281,3 +281,32 @@ def test_process_tests_target_branch_callback() -> None:
         param_mock,
         "",
     )
+
+
+def test_junit_file_not_found_error_message() -> None:
+    """Test that a helpful error message is shown when JUnit file doesn't exist."""
+    runner = testing.CliRunner()
+
+    # Set up minimal environment variables
+    env = {
+        "MERGIFY_API_URL": "https://api.mergify.com",
+        "MERGIFY_TOKEN": "abc",
+        "GITHUB_REPOSITORY": "user/repo",
+        "GITHUB_BASE_REF": "main",
+    }
+
+    with runner.isolated_filesystem():
+        # Try to run junit-process with a non-existent file
+        result = runner.invoke(
+            cli_junit_upload.junit_process,
+            ["non_existent_junit.xml"],
+            env=env,
+        )
+
+        assert result.exit_code == 2  # Click parameter validation error
+        assert "non_existent_junit.xml" in result.output
+        assert "does not exist" in result.output
+        assert "previous CI step failed" in result.output
+        assert (
+            "check if your test execution step completed successfully" in result.output
+        )