Add options to the compose loader

cli/compose/interpolation/interpolation.go

@@ -14,6 +14,8 @@ type Options struct {
 	LookupValue LookupValue
 	// TypeCastMapping maps key paths to functions to cast to a type
 	TypeCastMapping map[Path]Cast
+	// Substitution function to use
+	Substitute func(string, template.Mapping) (string, error)
 }
 
 // LookupValue is a function which maps from variable names to values.
@@ -33,6 +35,9 @@ func Interpolate(config map[string]interface{}, opts Options) (map[string]interf
 	if opts.TypeCastMapping == nil {
 		opts.TypeCastMapping = make(map[Path]Cast)
 	}
+	if opts.Substitute == nil {
+		opts.Substitute = template.Substitute
+	}
 
 	out := map[string]interface{}{}
 
@@ -51,7 +56,7 @@ func recursiveInterpolate(value interface{}, path Path, opts Options) (interface
 	switch value := value.(type) {
 
 	case string:
-		newValue, err := template.Substitute(value, template.Mapping(opts.LookupValue))
+		newValue, err := opts.Substitute(value, template.Mapping(opts.LookupValue))
 		if err != nil || newValue == value {
 			return value, newPathError(path, err)
 		}

cli/compose/loader/interpolate.go

@@ -64,11 +64,6 @@ func toBoolean(value string) (interface{}, error) {
 	}
 }
 
-func interpolateConfig(configDict map[string]interface{}, lookupEnv interp.LookupValue) (map[string]interface{}, error) {
-	return interp.Interpolate(
-		configDict,
-		interp.Options{
-			LookupValue:     lookupEnv,
-			TypeCastMapping: interpolateTypeCastMapping,
-		})
+func interpolateConfig(configDict map[string]interface{}, opts interp.Options) (map[string]interface{}, error) {
+	return interp.Interpolate(configDict, opts)
 }

cli/compose/loader/loader.go

@@ -8,6 +8,7 @@ import (
 	"sort"
 	"strings"
 
+	interp "github.com/docker/cli/cli/compose/interpolation"
 	"github.com/docker/cli/cli/compose/schema"
 	"github.com/docker/cli/cli/compose/template"
 	"github.com/docker/cli/cli/compose/types"
@@ -22,6 +23,16 @@ import (
 	yaml "gopkg.in/yaml.v2"
 )
 
+// Options supported by Load
+type Options struct {
+	// Skip schema validation
+	SkipValidation bool
+	// Skip interpolation
+	SkipInterpolation bool
+	// Interpolation options
+	Interpolate *interp.Options
+}
+
 // ParseYAML reads the bytes from a file, parses the bytes into a mapping
 // structure, and returns it.
 func ParseYAML(source []byte) (map[string]interface{}, error) {
@@ -41,12 +52,25 @@ func ParseYAML(source []byte) (map[string]interface{}, error) {
 }
 
 // Load reads a ConfigDetails and returns a fully loaded configuration
-func Load(configDetails types.ConfigDetails) (*types.Config, error) {
+func Load(configDetails types.ConfigDetails, options ...func(*Options)) (*types.Config, error) {
 	if len(configDetails.ConfigFiles) < 1 {
 		return nil, errors.Errorf("No files specified")
 	}
 
+	opts := &Options{
+		Interpolate: &interp.Options{
+			Substitute:      template.Substitute,
+			LookupValue:     configDetails.LookupEnv,
+			TypeCastMapping: interpolateTypeCastMapping,
+		},
+	}
+
+	for _, op := range options {
+		op(opts)
+	}
+
 	configs := []*types.Config{}
+	var err error
 
 	for _, file := range configDetails.ConfigFiles {
 		configDict := file.Config
@@ -62,14 +86,17 @@ func Load(configDetails types.ConfigDetails) (*types.Config, error) {
 			return nil, err
 		}
 
-		var err error
-		configDict, err = interpolateConfig(configDict, configDetails.LookupEnv)
-		if err != nil {
-			return nil, err
+		if !opts.SkipInterpolation {
+			configDict, err = interpolateConfig(configDict, *opts.Interpolate)
+			if err != nil {
+				return nil, err
+			}
 		}
 
-		if err := schema.Validate(configDict, configDetails.Version); err != nil {
-			return nil, err
+		if !opts.SkipValidation {
+			if err := schema.Validate(configDict, configDetails.Version); err != nil {
+				return nil, err
+			}
 		}
 
 		cfg, err := loadSections(configDict, configDetails)

cli/compose/template/template.go

@@ -16,6 +16,14 @@ var patternString = fmt.Sprintf(
 
 var pattern = regexp.MustCompile(patternString)
 
+// DefaultSubstituteFuncs contains the default SubstitueFunc used by the docker cli
+var DefaultSubstituteFuncs = []SubstituteFunc{
+	softDefault,
+	hardDefault,
+	requiredNonEmpty,
+	required,
+}
+
 // InvalidTemplateError is returned when a variable template is not in a valid
 // format
 type InvalidTemplateError struct {
@@ -32,8 +40,14 @@ func (e InvalidTemplateError) Error() string {
 // and the absence of a value.
 type Mapping func(string) (string, bool)
 
-// Substitute variables in the string with their values
-func Substitute(template string, mapping Mapping) (string, error) {
+// SubstituteFunc is a user-supplied function that apply substitution.
+// Returns the value as a string, a bool indicating if the function could apply
+// the substitution and an error.
+type SubstituteFunc func(string, Mapping) (string, bool, error)
+
+// SubstituteWith subsitute variables in the string with their values.
+// It accepts additional substitute function.
+func SubstituteWith(template string, mapping Mapping, pattern *regexp.Regexp, subsFuncs ...SubstituteFunc) (string, error) {
 	var err error
 	result := pattern.ReplaceAllStringFunc(template, func(substring string) string {
 		matches := pattern.FindStringSubmatch(substring)
@@ -47,49 +61,22 @@ func Substitute(template string, mapping Mapping) (string, error) {
 			substitution = groups["braced"]
 		}
 
-		switch {
-
-		case substitution == "":
+		if substitution == "" {
 			err = &InvalidTemplateError{Template: template}
 			return ""
+		}
 
-		// Soft default (fall back if unset or empty)
-		case strings.Contains(substitution, ":-"):
-			name, defaultValue := partition(substitution, ":-")
-			value, ok := mapping(name)
-			if !ok || value == "" {
-				return defaultValue
-			}
-			return value
-
-		// Hard default (fall back if-and-only-if empty)
-		case strings.Contains(substitution, "-"):
-			name, defaultValue := partition(substitution, "-")
-			value, ok := mapping(name)
-			if !ok {
-				return defaultValue
-			}
-			return value
-
-		case strings.Contains(substitution, ":?"):
-			name, errorMessage := partition(substitution, ":?")
-			value, ok := mapping(name)
-			if !ok || value == "" {
-				err = &InvalidTemplateError{
-					Template: fmt.Sprintf("required variable %s is missing a value: %s", name, errorMessage),
-				}
+		for _, f := range subsFuncs {
+			var (
+				value   string
+				applied bool
+			)
+			value, applied, err = f(substitution, mapping)
+			if err != nil {
 				return ""
 			}
-			return value
-
-		case strings.Contains(substitution, "?"):
-			name, errorMessage := partition(substitution, "?")
-			value, ok := mapping(name)
-			if !ok {
-				err = &InvalidTemplateError{
-					Template: fmt.Sprintf("required variable %s is missing a value: %s", name, errorMessage),
-				}
-				return ""
+			if !applied {
+				continue
 			}
 			return value
 		}
@@ -101,6 +88,65 @@ func Substitute(template string, mapping Mapping) (string, error) {
 	return result, err
 }
 
+// Substitute variables in the string with their values
+func Substitute(template string, mapping Mapping) (string, error) {
+	return SubstituteWith(template, mapping, pattern, DefaultSubstituteFuncs...)
+}
+
+// Soft default (fall back if unset or empty)
+func softDefault(substitution string, mapping Mapping) (string, bool, error) {
+	if !strings.Contains(substitution, ":-") {
+		return "", false, nil
+	}
+	name, defaultValue := partition(substitution, ":-")
+	value, ok := mapping(name)
+	if !ok || value == "" {
+		return defaultValue, true, nil
+	}
+	return value, true, nil
+}
+
+// Hard default (fall back if-and-only-if empty)
+func hardDefault(substitution string, mapping Mapping) (string, bool, error) {
+	if !strings.Contains(substitution, "-") {
+		return "", false, nil
+	}
+	name, defaultValue := partition(substitution, "-")
+	value, ok := mapping(name)
+	if !ok {
+		return defaultValue, true, nil
+	}
+	return value, true, nil
+}
+
+func requiredNonEmpty(substitution string, mapping Mapping) (string, bool, error) {
+	if !strings.Contains(substitution, ":?") {
+		return "", false, nil
+	}
+	name, errorMessage := partition(substitution, ":?")
+	value, ok := mapping(name)
+	if !ok || value == "" {
+		return "", true, &InvalidTemplateError{
+			Template: fmt.Sprintf("required variable %s is missing a value: %s", name, errorMessage),
+		}
+	}
+	return value, true, nil
+}
+
+func required(substitution string, mapping Mapping) (string, bool, error) {
+	if !strings.Contains(substitution, "?") {
+		return "", false, nil
+	}
+	name, errorMessage := partition(substitution, "?")
+	value, ok := mapping(name)
+	if !ok {
+		return "", true, &InvalidTemplateError{
+			Template: fmt.Sprintf("required variable %s is missing a value: %s", name, errorMessage),
+		}
+	}
+	return value, true, nil
+}
+
 func matchGroups(matches []string) map[string]string {
 	groups := make(map[string]string)
 	for i, name := range pattern.SubexpNames()[1:] {

cli/compose/template/template_test.go

@@ -1,6 +1,7 @@
 package template
 
 import (
+	"fmt"
 	"reflect"
 	"testing"
 
@@ -148,3 +149,26 @@ func TestDefaultsForMandatoryVariables(t *testing.T) {
 		assert.Check(t, is.Equal(tc.expected, result))
 	}
 }
+
+func TestSubstituteWithCustomFunc(t *testing.T) {
+	errIsMissing := func(substitution string, mapping Mapping) (string, bool, error) {
+		value, found := mapping(substitution)
+		if !found {
+			return "", true, &InvalidTemplateError{
+				Template: fmt.Sprintf("required variable %s is missing a value", substitution),
+			}
+		}
+		return value, true, nil
+	}
+
+	result, err := SubstituteWith("ok ${FOO}", defaultMapping, pattern, errIsMissing)
+	assert.NilError(t, err)
+	assert.Check(t, is.Equal("ok first", result))
+
+	result, err = SubstituteWith("ok ${BAR}", defaultMapping, pattern, errIsMissing)
+	assert.NilError(t, err)
+	assert.Check(t, is.Equal("ok ", result))
+
+	_, err = SubstituteWith("ok ${NOTHERE}", defaultMapping, pattern, errIsMissing)
+	assert.Check(t, is.ErrorContains(err, "required variable"))
+}