Print full dockerfile path instead of context on error

Current error message does not provide the exact path where the
Dockerfile is being searched.

This commit distinguishes two types of errors when Dockerfile is not
found in build context:
- when the context does not have provided custom-named Dockerfile, the
path in the error message is absolute: "OSError: Dockerfile not found in
.../podman-compose/tests/integration/build_fail/context_no_file/custom-named-Dockerfile"
- when the context does not have any Dockerfile, the path in the error
message is: "OSError: Dockerfile not found in
.../podman-compose/tests/integration/build_fail/context_no_file"
Only this error message was used before the fix.

Signed-off-by: Monika Kairaityte <monika@kibit.lt>
Co-authored-by: Siteshwar Vashisht <svashisht@redhat.com>

podman_compose.py

@@ -2752,8 +2752,10 @@ def container_to_build_args(
     build_args = []
 
     if not is_path_git_url(ctx):
+        custom_dockerfile_given = False
         if dockerfile:
             dockerfile = os.path.join(ctx, dockerfile)
+            custom_dockerfile_given = True
         else:
             dockerfile_alts = [
                 "Containerfile",
@@ -2773,6 +2775,9 @@ def container_to_build_args(
             dockerfile = os.path.normpath(os.path.join(ctx, dockerfile))
             build_args.extend(["-f", dockerfile])
         else:
+            if custom_dockerfile_given:
+                # custom dockerfile name was also not found in the file system
+                raise OSError(f"Dockerfile not found in {dockerfile}")
             raise OSError(f"Dockerfile not found in {ctx}")
 
     build_args.extend(["-t", cnt["image"]])

tests/integration/build_fail/context_no_file/NotDockerfile

@@ -0,0 +1 @@
+test

tests/integration/build_fail/docker-compose.yml

@@ -3,3 +3,12 @@ services:
     test:
       build: ./context
       image: build-fail-img
+    test_no_dockerfile:
+      build:
+        context: ./context_no_file
+      image: busybox
+    test_no_custom_dockerfile:
+      build:
+        context: ./context_no_file
+        dockerfile: Dockerfile-alt
+      image: busybox

tests/integration/build_fail/test_podman_compose_build_fail.py

@@ -22,9 +22,48 @@ class TestComposeBuildFail(unittest.TestCase, RunSubprocessMixin):
                 "-f",
                 compose_yaml_path(),
                 "build",
+                "test",
             ],
             expected_returncode=127,
         )
         self.assertIn("RUN this_command_does_not_exist", str(output))
         self.assertIn("this_command_does_not_exist: not found", str(error))
         self.assertIn("while running runtime: exit status 127", str(error))
+
+    def test_dockerfile_does_not_exist(self):
+        out, error = self.run_subprocess_assert_returncode(
+            [
+                podman_compose_path(),
+                "-f",
+                compose_yaml_path(),
+                "build",
+                "test_no_dockerfile",
+            ],
+            expected_returncode=1,
+        )
+        error = error.decode('utf-8')
+        result = '\n'.join(error.splitlines()[-1:])
+
+        expected_path = os.path.join(os.path.dirname(__file__), "context_no_file")
+        expected = f'OSError: Dockerfile not found in {expected_path}'
+
+        self.assertEqual(expected, result)
+
+    def test_custom_dockerfile_does_not_exist(self):
+        out, error = self.run_subprocess_assert_returncode(
+            [
+                podman_compose_path(),
+                "-f",
+                compose_yaml_path(),
+                "build",
+                "test_no_custom_dockerfile",
+            ],
+            expected_returncode=1,
+        )
+        error = error.decode('utf-8')
+        result = '\n'.join(error.splitlines()[-1:])
+
+        expected_path = os.path.join(os.path.dirname(__file__), "context_no_file/Dockerfile-alt")
+        expected = f'OSError: Dockerfile not found in {expected_path}'
+
+        self.assertEqual(expected, result)