Merge pull request #125 from LeastAuthority/report-git-failure-output

Report git's output when git fails

src/towncrier/check.py

@@ -8,7 +8,11 @@
 
 import click
 
-from subprocess import check_output, STDOUT
+from subprocess import (
+    CalledProcessError,
+    check_output,
+    STDOUT,
+)
 
 from ._settings import load_config, load_config_from_file
 from ._builder import find_fragments
@@ -34,11 +38,16 @@ def __main(comparewith, directory, pyproject):
     else:
         config = load_config_from_file(pyproject)
 
-    files_changed = (
-        _run(["git", "diff", "--name-only", comparewith + "..."], cwd=base_directory)
-        .decode(getattr(sys.stdout, "encoding", "utf8"))
-        .strip()
-    )
+    try:
+        files_changed = (
+            _run(["git", "diff", "--name-only", comparewith + "..."], cwd=base_directory)
+            .decode(getattr(sys.stdout, "encoding", "utf8"))
+            .strip()
+        )
+    except CalledProcessError as e:
+        click.echo("git produced output while failing:")
+        click.echo(e.output)
+        raise
 
     if not files_changed:
         click.echo("On trunk, or no diffs, so no newsfragment required.")

src/towncrier/newsfragments/124.feature

@@ -0,0 +1 @@
+towncrier.check now reports git output when it encounters a git failure.

src/towncrier/test/test_check.py

@@ -10,9 +10,47 @@
 from towncrier.check import _main
 
 
+def create_project(pyproject_path):
+    with open(pyproject_path, "w") as f:
+        f.write("[tool.towncrier]\n" 'package = "foo"\n')
+    os.mkdir("foo")
+    with open("foo/__init__.py", "w") as f:
+        f.write('__version__ = "1.2.3"\n')
+    os.mkdir("foo/newsfragments")
+    fragment_path = "foo/newsfragments/123.feature"
+    with open(fragment_path, "w") as f:
+        f.write("Adds levitation")
+
+    call(["git", "init"])
+    call(["git", "config", "user.name", "user"])
+    call(["git", "config", "user.email", "[email protected]"])
+    call(["git", "add", "."])
+    call(["git", "commit", "-m", "Initial Commit"])
+    call(["git", "checkout", "-b", "otherbranch"])
+
+
 class TestChecker(TestCase):
     maxDiff = None
 
+    def test_git_fails(self):
+        """
+        If git fails to report a comparison, git's output is reported to aid in
+        debugging the situation.
+        """
+        runner = CliRunner()
+        with runner.isolated_filesystem():
+            create_project("pyproject.toml")
+
+            result = runner.invoke(_main, ["--compare-with", "hblaugh"])
+            self.assertIn(
+                "git produced output while failing",
+                result.output,
+            )
+            self.assertIn(
+                "hblaugh",
+                result.output,
+            )
+
     def test_no_changes_made(self):
         self._test_no_changes_made(
             "pyproject.toml",
@@ -33,22 +71,7 @@ def _test_no_changes_made(self, pyproject_path, invoke):
         runner = CliRunner()
 
         with runner.isolated_filesystem():
-            with open(pyproject_path, "w") as f:
-                f.write("[tool.towncrier]\n" 'package = "foo"\n')
-            os.mkdir("foo")
-            with open("foo/__init__.py", "w") as f:
-                f.write('__version__ = "1.2.3"\n')
-            os.mkdir("foo/newsfragments")
-            fragment_path = "foo/newsfragments/123.feature"
-            with open(fragment_path, "w") as f:
-                f.write("Adds levitation")
-
-            call(["git", "init"])
-            call(["git", "config", "user.name", "user"])
-            call(["git", "config", "user.email", "[email protected]"])
-            call(["git", "add", "."])
-            call(["git", "commit", "-m", "Initial Commit"])
-            call(["git", "checkout", "-b", "otherbranch"])
+            create_project(pyproject_path)
 
             result = invoke(runner, _main, ["--compare-with", "master"])
 
@@ -61,22 +84,7 @@ def test_fragment_exists(self):
         runner = CliRunner()
 
         with runner.isolated_filesystem():
-            with open("pyproject.toml", "w") as f:
-                f.write("[tool.towncrier]\n" 'package = "foo"\n')
-            os.mkdir("foo")
-            with open("foo/__init__.py", "w") as f:
-                f.write('__version__ = "1.2.3"\n')
-            os.mkdir("foo/newsfragments")
-            fragment_path = "foo/newsfragments/123.feature"
-            with open(fragment_path, "w") as f:
-                f.write("Adds levitation")
-
-            call(["git", "init"])
-            call(["git", "config", "user.name", "user"])
-            call(["git", "config", "user.email", "[email protected]"])
-            call(["git", "add", "."])
-            call(["git", "commit", "-m", "Initial Commit"])
-            call(["git", "checkout", "-b", "otherbranch"])
+            create_project("pyproject.toml")
 
             file_path = "foo/somefile.py"
             with open(file_path, "w") as f:
@@ -110,22 +118,7 @@ def test_fragment_missing(self):
         runner = CliRunner()
 
         with runner.isolated_filesystem():
-            with open("pyproject.toml", "w") as f:
-                f.write("[tool.towncrier]\n" 'package = "foo"\n')
-            os.mkdir("foo")
-            with open("foo/__init__.py", "w") as f:
-                f.write('__version__ = "1.2.3"\n')
-            os.mkdir("foo/newsfragments")
-            fragment_path = "foo/newsfragments/123.feature"
-            with open(fragment_path, "w") as f:
-                f.write("Adds levitation")
-
-            call(["git", "init"])
-            call(["git", "config", "user.name", "user"])
-            call(["git", "config", "user.email", "[email protected]"])
-            call(["git", "add", "."])
-            call(["git", "commit", "-m", "Initial Commit"])
-            call(["git", "checkout", "-b", "otherbranch"])
+            create_project("pyproject.toml")
 
             file_path = "foo/somefile.py"
             with open(file_path, "w") as f: