bake: x-bake extension field with compose

Signed-off-by: CrazyMax <crazy-max@users.noreply.github.com>

bake/compose.go

@@ -80,13 +80,15 @@ func ParseCompose(dt []byte) (*Config, error) {
 					return val, ok
 				})),
 				CacheFrom: s.Build.CacheFrom,
-				// TODO: add platforms
+			}
+			if err = t.composeExtTarget(s.Build.Extensions); err != nil {
+				return nil, err
 			}
 			if s.Build.Target != "" {
 				target := s.Build.Target
 				t.Target = &target
 			}
-			if s.Image != "" {
+			if len(t.Tags) == 0 && s.Image != "" {
 				t.Tags = []string{s.Image}
 			}
 			c.Targets = append(c.Targets, t)
@@ -111,3 +113,82 @@ func flatten(in compose.MappingWithEquals) compose.Mapping {
 	}
 	return out
 }
+
+// composeExtTarget converts Compose build extension x-bake to bake Target
+// https://github.com/compose-spec/compose-spec/blob/master/spec.md#extension
+func (t *Target) composeExtTarget(exts map[string]interface{}) error {
+	if ext, ok := exts["x-bake"]; ok {
+		for key, val := range ext.(map[string]interface{}) {
+			switch key {
+			case "tags":
+				if res, k := val.(string); k {
+					t.Tags = append(t.Tags, res)
+				} else {
+					for _, res := range val.([]interface{}) {
+						t.Tags = append(t.Tags, res.(string))
+					}
+				}
+			case "cache-from":
+				t.CacheFrom = []string{} // Needed to override the main field
+				if res, k := val.(string); k {
+					t.CacheFrom = append(t.CacheFrom, res)
+				} else {
+					for _, res := range val.([]interface{}) {
+						t.CacheFrom = append(t.CacheFrom, res.(string))
+					}
+				}
+			case "cache-to":
+				if res, k := val.(string); k {
+					t.CacheTo = append(t.CacheTo, res)
+				} else {
+					for _, res := range val.([]interface{}) {
+						t.CacheTo = append(t.CacheTo, res.(string))
+					}
+				}
+			case "secret":
+				if res, k := val.(string); k {
+					t.Secrets = append(t.Secrets, res)
+				} else {
+					for _, res := range val.([]interface{}) {
+						t.Secrets = append(t.Secrets, res.(string))
+					}
+				}
+			case "ssh":
+				if res, k := val.(string); k {
+					t.SSH = append(t.SSH, res)
+				} else {
+					for _, res := range val.([]interface{}) {
+						t.SSH = append(t.SSH, res.(string))
+					}
+				}
+			case "platforms":
+				if res, k := val.(string); k {
+					t.Platforms = append(t.Platforms, res)
+				} else {
+					for _, res := range val.([]interface{}) {
+						t.Platforms = append(t.Platforms, res.(string))
+					}
+				}
+			case "output":
+				if res, k := val.(string); k {
+					t.Outputs = append(t.Outputs, res)
+				} else {
+					for _, res := range val.([]interface{}) {
+						t.Outputs = append(t.Outputs, res.(string))
+					}
+				}
+			case "pull":
+				if res, ok := val.(bool); ok {
+					t.Pull = &res
+				}
+			case "no-cache":
+				if res, ok := val.(bool); ok {
+					t.NoCache = &res
+				}
+			default:
+				return fmt.Errorf("compose file invalid: unkwown %s field for x-bake", key)
+			}
+		}
+	}
+	return nil
+}