enforce unicity after canonical transformation

loader/extends_test.go

@@ -170,3 +170,35 @@ services:
 	})
 	assert.NilError(t, err)
 }
+
+func TestExtendsPortOverride(t *testing.T) {
+	yaml := `
+name: test-extends-port
+services:
+  test:
+    extends:
+      file: testdata/extends/ports.yaml
+      service: test
+`
+	abs, err := filepath.Abs(".")
+	assert.NilError(t, err)
+
+	p, err := LoadWithContext(context.Background(), types.ConfigDetails{
+		ConfigFiles: []types.ConfigFile{
+			{
+				Filename: "testdata/extends/ports.yaml",
+			},
+			{
+				Content:  []byte(yaml),
+				Filename: "(override)",
+			},
+		},
+		WorkingDir: abs,
+	}, func(options *Options) {
+		options.ResolvePaths = false
+		options.SkipValidation = true
+	})
+	assert.NilError(t, err)
+	assert.Equal(t, len(p.Services["test"].Ports), 1)
+
+}

loader/loader.go

@@ -403,6 +403,12 @@ func loadYamlModel(ctx context.Context, config types.ConfigDetails, opts *Option
 		return nil, err
 	}
 
+	// Canonical transformation can reveal duplicates, typically as ports can be a range and conflict with an override
+	dict, err = override.EnforceUnicity(dict)
+	if err != nil {
+		return nil, err
+	}
+
 	if !opts.SkipInclude {
 		included = append(included, config.ConfigFiles[0].Filename)
 		err = ApplyInclude(ctx, config, dict, opts, included)

loader/testdata/extends/ports.yaml

@@ -0,0 +1,5 @@
+services:
+  test:
+    image: test
+    ports:
+      - 8080:8080