Fix invalid path error when using OCI artifacts on Windows

When using OCI artifacts (e.g., `docker compose -f oci://dockersamples/welcome-to-docker up`)
on Windows, users encountered the following error:

  CreateFile C:\Users\username\oci:\dockersamples\.env: The filename, directory name,
  or volume label syntax is incorrect.

This issue was introduced between v5.0.0 and v5.0.1, specifically by commit 6c04392
which fixed error handling in setEnvWithDotEnv. The bug existed in v5.0.0 but was
silently ignored due to improper error handling.

Root Cause:
-----------
The setEnvWithDotEnv function creates ProjectOptions without registering remote loaders.
Without remote loaders, the compose-go library doesn't recognize OCI paths as remote
resources. It falls through to filepath.Abs() which treats the OCI reference as a
relative path.

On Windows, filepath.Abs("oci://dockersamples/...") produces an invalid path like:
  C:\Users\username\oci:\dockersamples

Windows rejects this path because colons are only valid after drive letters.

Solution:
---------
Modified setEnvWithDotEnv to detect remote config paths and skip environment loading
for them. Instead of hardcoding string checks, the fix uses the actual remote loaders'
Accept() method to determine if a config path is remote. This is more maintainable
and consistent with how the compose-go library identifies remote resources.

The function now:
- Accepts a dockerCli parameter to access remote loaders
- Uses opts.remoteLoaders(dockerCli) to get loader instances
- Checks if any loader accepts the config path using loader.Accept()
- Skips .env loading for remote configs (happens later when loaders are initialized)
- Allows normal processing for local compose files

Testing:
--------
- Added tests for OCI artifacts, Git remotes, and local paths
- Verified fix works on Windows ARM64
- All existing tests pass

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
Signed-off-by: Michael Irwin <mikesir87@gmail.com>

Author: 2 people

cmd/compose/compose.go

@@ -477,7 +477,7 @@ func RootCommand(dockerCli command.Cli, backendOptions *BackendOptions) *cobra.C
 				logrus.SetLevel(logrus.TraceLevel)
 			}
 
-			err := setEnvWithDotEnv(opts)
+			err := setEnvWithDotEnv(opts, dockerCli)
 			if err != nil {
 				return err
 			}
@@ -677,7 +677,21 @@ func stdinfo(dockerCli command.Cli) io.Writer {
 	return dockerCli.Err()
 }
 
-func setEnvWithDotEnv(opts ProjectOptions) error {
+func setEnvWithDotEnv(opts ProjectOptions, dockerCli command.Cli) error {
+	// Check if we're using a remote config (OCI or Git)
+	// If so, skip env loading as remote loaders haven't been initialized yet
+	// and trying to process the path would fail
+	remoteLoaders := opts.remoteLoaders(dockerCli)
+	for _, path := range opts.ConfigPaths {
+		for _, loader := range remoteLoaders {
+			if loader.Accept(path) {
+				// Remote config - skip env loading for now
+				// It will be loaded later when the project is fully initialized
+				return nil
+			}
+		}
+	}
+
 	options, err := cli.NewProjectOptions(opts.ConfigPaths,
 		cli.WithWorkingDirectory(opts.ProjectDir),
 		cli.WithOsEnv,

cmd/compose/compose_oci_test.go

@@ -0,0 +1,76 @@
+/*
+   Copyright 2020 Docker Compose CLI authors
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package compose
+
+import (
+	"testing"
+
+	"go.uber.org/mock/gomock"
+	"gotest.tools/v3/assert"
+
+	"github.com/docker/compose/v5/pkg/mocks"
+)
+
+func TestSetEnvWithDotEnv_WithOCIArtifact(t *testing.T) {
+	// Test that setEnvWithDotEnv doesn't fail when using OCI artifacts
+	ctrl := gomock.NewController(t)
+	defer ctrl.Finish()
+	cli := mocks.NewMockCli(ctrl)
+
+	opts := ProjectOptions{
+		ConfigPaths: []string{"oci://docker.io/dockersamples/welcome-to-docker"},
+		ProjectDir:  "",
+		EnvFiles:    []string{},
+	}
+
+	err := setEnvWithDotEnv(opts, cli)
+	assert.NilError(t, err, "setEnvWithDotEnv should not fail with OCI artifact path")
+}
+
+func TestSetEnvWithDotEnv_WithGitRemote(t *testing.T) {
+	// Test that setEnvWithDotEnv doesn't fail when using Git remotes
+	ctrl := gomock.NewController(t)
+	defer ctrl.Finish()
+	cli := mocks.NewMockCli(ctrl)
+
+	opts := ProjectOptions{
+		ConfigPaths: []string{"https://github.com/docker/compose.git"},
+		ProjectDir:  "",
+		EnvFiles:    []string{},
+	}
+
+	err := setEnvWithDotEnv(opts, cli)
+	assert.NilError(t, err, "setEnvWithDotEnv should not fail with Git remote path")
+}
+
+func TestSetEnvWithDotEnv_WithLocalPath(t *testing.T) {
+	// Test that setEnvWithDotEnv still works with local paths
+	// This will fail if the file doesn't exist, but it should not panic
+	// or produce invalid paths
+	ctrl := gomock.NewController(t)
+	defer ctrl.Finish()
+	cli := mocks.NewMockCli(ctrl)
+
+	opts := ProjectOptions{
+		ConfigPaths: []string{"compose.yaml"},
+		ProjectDir:  "",
+		EnvFiles:    []string{},
+	}
+
+	// This may error if files don't exist, but should not panic
+	_ = setEnvWithDotEnv(opts, cli)
+}