Remove Path field from SourceContext

Also:
- update `processArgs` to do substitutions inline.
- update `fillDefaults` to set the default Source.Path to `"."` when the
  Source type is Context.

Signed-off-by: Peter Engelbert <pmengelbert@gmail.com>

docs/spec.schema.json

@@ -483,14 +483,13 @@
 		"SourceContext": {
 			"properties": {
 				"name": {
-					"type": "string"
-				},
-				"path": {
-					"type": "string"
+					"type": "string",
+					"description": "Name is the name of the build context. By default, it is the magic name\n`context`, recognized by Docker as the default context."
 				}
 			},
 			"additionalProperties": false,
-			"type": "object"
+			"type": "object",
+			"description": "SourceContext is used to generate a source from a build context."
 		},
 		"SourceDockerImage": {
 			"properties": {

load.go

@@ -27,64 +27,56 @@ const DefaultPatchStrip int = 1
 func (s *Source) processArgs(args map[string]string) error {
 	lex := shell.NewLex('\\')
 
-	var sub *string
+	sub := func(s *string) error {
+		updated, err := lex.ProcessWordWithMap(*s, args)
+		if err != nil {
+			return err
+		}
+		*s = updated
+		return nil
+	}
+
 	switch {
 	case s.DockerImage != nil:
 		for _, mnt := range s.DockerImage.Cmd.Mounts {
 			if err := mnt.Spec.processArgs(args); err != nil {
 				return err
 			}
 		}
-		sub = &s.DockerImage.Ref
+		sub(&s.DockerImage.Ref)
 	case s.Git != nil:
-		sub = &s.Git.URL
+		fields := []*string{
+			&s.Git.URL,
+			&s.Git.Commit,
+		}
+		for _, f := range fields {
+			if err := sub(f); err != nil {
+				return err
+			}
+		}
 	case s.HTTPS != nil:
-		sub = &s.HTTPS.URL
+		sub(&s.HTTPS.URL)
 	case s.Context != nil:
-		updated, err := lex.ProcessWordWithMap(s.Context.Name, args)
-		if err != nil {
-			return err
-		}
-		s.Context.Name = updated
-
-		updated, err = lex.ProcessWordWithMap(s.Context.Path, args)
-		if err != nil {
+		if err := sub(&s.Context.Name); err != nil {
 			return err
 		}
-		s.Context.Path = updated
-
-		sub = nil
 	case s.Build != nil:
 		if err := s.Build.Source.processArgs(args); err != nil {
 			return err
 		}
 
-		updated, err := lex.ProcessWordWithMap(s.Build.DockerFile, args)
-		if err != nil {
-			return err
+		fields := []*string{
+			&s.Build.DockerFile,
+			&s.Build.Target,
 		}
-		s.Build.DockerFile = updated
-
-		updated, err = lex.ProcessWordWithMap(s.Build.Target, args)
-		if err != nil {
-			return err
+		for _, f := range fields {
+			if err := sub(f); err != nil {
+				return err
+			}
 		}
-		s.Build.Target = updated
-
-		sub = nil
 	default:
 	}
 
-	if sub == nil {
-		return nil
-	}
-
-	updated, err := lex.ProcessWordWithMap(*sub, args)
-	if err != nil {
-		return err
-	}
-
-	*sub = updated
 	return nil
 }
 
@@ -100,8 +92,8 @@ func fillDefaults(s *Source) {
 		if s.Context.Name == "" {
 			s.Context.Name = dockerui.DefaultLocalNameContext
 		}
-		if s.Context.Path == "" {
-			s.Context.Path = "."
+		if s.Path == "" {
+			s.Path = "."
 		}
 	case s.Build != nil:
 		fillDefaults(&s.Build.Source)

source.go

@@ -186,18 +186,12 @@ func source2LLBGetter(s *Spec, src Source, name string, forMount bool) LLBGetter
 			opts = append(opts, llb.Filename(name))
 			return llb.HTTP(https.URL, opts...), nil
 		case src.Context != nil:
-			srcCtx := src.Context
-
 			st, err := sOpt.GetContext(dockerui.DefaultLocalNameContext, localIncludeExcludeMerge(&src))
 			if err != nil {
 				return llb.Scratch(), err
 			}
 
 			includeExcludeHandled = true
-			if src.Path == "" && srcCtx.Path != "" {
-				src.Path = srcCtx.Path
-			}
-
 			return *st, nil
 		case src.Build != nil:
 			build := src.Build

spec.go

@@ -194,9 +194,12 @@ type SourceHTTPS struct {
 	URL string `yaml:"url" json:"url"`
 }
 
+// SourceContext is used to generate a source from a build context. The path to
+// the build context is provided to the `Path` field of the owning `Source`.
 type SourceContext struct {
+	// Name is the name of the build context. By default, it is the magic name
+	// `context`, recognized by Docker as the default context.
 	Name string `yaml:"name,omitempty" json:"name,omitempty"`
-	Path string `yaml:"path,omitempty" json:"path,omitempty"`
 }
 
 // SourceBuild is used to generate source from a DockerFile build, either