fix: compose variables are now interpolated from .env file (fixes #144)

pkg/client/compose/project.go

@@ -16,7 +16,10 @@ func LoadProject(ctx context.Context, paths []string, opts ...composecli.Project
 		composecli.WithName(FakeProjectName),
 		// First apply os.Environment, always wins.
 		composecli.WithOsEnv,
-		// Read dot env file to populate project environment.
+		// Set the local .env file to be loaded by WithDotEnv. COMPOSE_DISABLE_ENV_FILE can disable it.
+		composecli.WithEnvFiles(),
+		// Read environment variables from .env files set by WithEnvFiles (.env by default) to make available
+		// for interpolation.
 		composecli.WithDotEnv,
 		// Get compose file path set by COMPOSE_FILE.
 		composecli.WithConfigFileEnv,

pkg/client/compose/project_test.go

@@ -0,0 +1,188 @@
+package compose
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// TestLoadProject_EnvFileInterpolation tests that environment variables from .env files
+// are properly loaded and available for interpolation in compose files.
+func TestLoadProject_EnvFileInterpolation(t *testing.T) {
+	tests := []struct {
+		name        string
+		composeYAML string
+		envFile     string
+		verify      func(t *testing.T, projectDir string)
+	}{
+		// This is a regression test for https://github.com/psviderski/uncloud/issues/144.
+		{
+			name: "simple variable interpolation",
+			envFile: `KEY1=value1
+KEY2=value2
+`,
+			composeYAML: `services:
+  web:
+    image: nginx
+    command: ["echo", "${KEY1}", "${KEY2}"]
+`,
+			verify: func(t *testing.T, projectDir string) {
+				project, err := LoadProject(context.Background(), []string{filepath.Join(projectDir, "compose.yaml")})
+				require.NoError(t, err)
+				require.NotNil(t, project)
+				require.Len(t, project.Services, 1)
+
+				webService := project.Services["web"]
+				require.NotNil(t, webService)
+				require.Len(t, webService.Command, 3)
+				assert.Equal(t, "echo", webService.Command[0])
+				assert.Equal(t, "value1", webService.Command[1], "KEY1 should be interpolated from .env file")
+				assert.Equal(t, "value2", webService.Command[2], "KEY2 should be interpolated from .env file")
+			},
+		},
+		{
+			name: "environment variable interpolation in service environment",
+			envFile: `DATABASE_URL=postgres://localhost:5432/mydb
+REDIS_URL=redis://localhost:6379
+`,
+			composeYAML: `services:
+  app:
+    image: myapp:latest
+    environment:
+      - DB_CONNECTION=${DATABASE_URL}
+      - CACHE_URL=${REDIS_URL}
+`,
+			verify: func(t *testing.T, projectDir string) {
+				project, err := LoadProject(context.Background(), []string{filepath.Join(projectDir, "compose.yaml")})
+				require.NoError(t, err)
+				require.NotNil(t, project)
+				require.Len(t, project.Services, 1)
+
+				appService := project.Services["app"]
+				require.NotNil(t, appService)
+				require.NotNil(t, appService.Environment)
+
+				assert.Equal(t, "postgres://localhost:5432/mydb", *appService.Environment["DB_CONNECTION"],
+					"DATABASE_URL should be interpolated from .env file")
+				assert.Equal(t, "redis://localhost:6379", *appService.Environment["CACHE_URL"],
+					"REDIS_URL should be interpolated from .env file")
+			},
+		},
+		{
+			name: "variable with default value when not in env file",
+			envFile: `EXISTING_VAR=exists
+`,
+			composeYAML: `services:
+  test:
+    image: busybox
+    environment:
+      - VAR1=${EXISTING_VAR}
+      - VAR2=${MISSING_VAR:-default_value}
+`,
+			verify: func(t *testing.T, projectDir string) {
+				project, err := LoadProject(context.Background(), []string{filepath.Join(projectDir, "compose.yaml")})
+				require.NoError(t, err)
+				require.NotNil(t, project)
+
+				testService := project.Services["test"]
+				require.NotNil(t, testService)
+
+				assert.Equal(t, "exists", *testService.Environment["VAR1"],
+					"EXISTING_VAR should be interpolated from .env file")
+				assert.Equal(t, "default_value", *testService.Environment["VAR2"],
+					"MISSING_VAR should use default value")
+			},
+		},
+		{
+			name: "os environment overrides .env file",
+			envFile: `MY_VAR=from_env_file
+`,
+			composeYAML: `services:
+  override:
+    image: alpine
+    environment:
+      - TEST_VAR=${MY_VAR}
+`,
+			verify: func(t *testing.T, projectDir string) {
+				t.Setenv("MY_VAR", "from_os_env")
+
+				project, err := LoadProject(context.Background(), []string{filepath.Join(projectDir, "compose.yaml")})
+				require.NoError(t, err)
+				require.NotNil(t, project)
+
+				overrideService := project.Services["override"]
+				require.NotNil(t, overrideService)
+
+				// OS environment should win over .env file (WithOsEnv comes before WithDotEnv).
+				assert.Equal(t, "from_os_env", *overrideService.Environment["TEST_VAR"],
+					"OS environment should override .env file")
+			},
+		},
+		{
+			name:    "no .env file - missing variables get empty string",
+			envFile: "",
+			composeYAML: `services:
+  missing:
+    image: ubuntu
+    command: ["echo", "${UNDEFINED_VAR}"]
+`,
+			verify: func(t *testing.T, projectDir string) {
+				os.Remove(filepath.Join(projectDir, ".env"))
+
+				project, err := LoadProject(context.Background(), []string{filepath.Join(projectDir, "compose.yaml")})
+				require.NoError(t, err)
+				require.NotNil(t, project)
+
+				missingService := project.Services["missing"]
+				require.NotNil(t, missingService)
+				require.Len(t, missingService.Command, 2)
+				assert.Equal(t, "", missingService.Command[1], "undefined variable should be empty string")
+			},
+		},
+		{
+			name:    "COMPOSE_DISABLE_ENV_FILE disables .env loading",
+			envFile: `MY_VAR=from_env_file`,
+			composeYAML: `services:
+  web:
+    image: nginx
+    command: ["echo", "${MY_VAR}"]
+`,
+			verify: func(t *testing.T, projectDir string) {
+				t.Setenv("COMPOSE_DISABLE_ENV_FILE", "true")
+
+				project, err := LoadProject(context.Background(), []string{filepath.Join(projectDir, "compose.yaml")})
+				require.NoError(t, err)
+				require.NotNil(t, project)
+
+				webService := project.Services["web"]
+				require.NotNil(t, webService)
+				require.Len(t, webService.Command, 2)
+
+				assert.Equal(t, "", webService.Command[1], "variable should be empty when .env file is disabled")
+			},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			tempDir := t.TempDir()
+
+			composeFile := filepath.Join(tempDir, "compose.yaml")
+			err := os.WriteFile(composeFile, []byte(tt.composeYAML), 0o644)
+			require.NoError(t, err)
+
+			// Write .env file if provided.
+			if tt.envFile != "" {
+				envFile := filepath.Join(tempDir, ".env")
+				err = os.WriteFile(envFile, []byte(tt.envFile), 0o644)
+				require.NoError(t, err)
+			}
+
+			tt.verify(t, tempDir)
+		})
+	}
+}