json: beginnings of parsing JSON into File objects

The returned file objects are not actually functional yet, but this
establishes the interface.

zcl/json/public.go

@@ -0,0 +1,70 @@
+package json
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+
+	"github.com/apparentlymart/go-zcl/zcl"
+)
+
+// Parse attempts to parse the given buffer as JSON and, if successful, returns
+// a zcl.File for the zcl configuration represented by it.
+//
+// This is not a generic JSON parser. Instead, it deals only with the profile
+// of JSON used to express zcl configuration.
+//
+// The returned file is valid if it is non-nil, regardless of whether the
+// diagnostics are also non-nil. If both are returned, the diagnostics should
+// still be presented to the user because they may contain warnings.
+func Parse(src []byte, filename string) (*zcl.File, zcl.Diagnostics) {
+	var file *zcl.File
+	rootNode, diags := parseFileContent(src, filename)
+	if _, ok := rootNode.(*objectVal); !ok {
+		return nil, diags.Append(&zcl.Diagnostic{
+			Severity: zcl.DiagError,
+			Summary:  "Root value must be object",
+			Detail:   "The root value in a JSON-based configuration must be a JSON object.",
+			Subject:  rootNode.StartRange().Ptr(),
+		})
+	}
+	if rootNode != nil {
+		file = &zcl.File{
+			Body: &body{
+				obj: rootNode.(*objectVal),
+			},
+		}
+	}
+	return file, diags
+}
+
+// ParseFile is a convenience wrapper around Parse that first attempts to load
+// data from the given filename, passing the result to Parse if successful.
+//
+// If the file cannot be read, an error diagnostic with nil context is returned.
+func ParseFile(filename string) (*zcl.File, zcl.Diagnostics) {
+	f, err := os.Open(filename)
+	if err != nil {
+		return nil, zcl.Diagnostics{
+			{
+				Severity: zcl.DiagError,
+				Summary:  "Failed to open file",
+				Detail:   fmt.Sprintf("The file %q could not be opened.", filename),
+			},
+		}
+	}
+	defer f.Close()
+
+	src, err := ioutil.ReadAll(f)
+	if err != nil {
+		return nil, zcl.Diagnostics{
+			{
+				Severity: zcl.DiagError,
+				Summary:  "Failed to read file",
+				Detail:   fmt.Sprintf("The file %q was opened, but an error occured while reading it.", filename),
+			},
+		}
+	}
+
+	return Parse(src, filename)
+}

zcl/json/public_test.go

@@ -0,0 +1,16 @@
+package json
+
+import (
+	"testing"
+)
+
+func TestParse_nonObject(t *testing.T) {
+	src := `true`
+	file, diags := Parse([]byte(src), "")
+	if len(diags) != 1 {
+		t.Errorf("got %d diagnostics; want 1", len(diags))
+	}
+	if file != nil {
+		t.Errorf("got non-nil File; want nil")
+	}
+}

zcl/json/structure.go

@@ -0,0 +1,32 @@
+package json
+
+import (
+	"github.com/apparentlymart/go-zcl/zcl"
+)
+
+// body is the implementation of "Body" used for files processed with the JSON
+// parser.
+type body struct {
+	obj *objectVal
+
+	// If non-nil, the keys of this map cause the corresponding attributes to
+	// be treated as non-existing. This is used when Body.PartialContent is
+	// called, to produce the "remaining content" Body.
+	hiddenAttrs map[string]struct{}
+}
+
+// expression is the implementation of "Expression" used for files processed
+// with the JSON parser.
+type expression struct {
+	src node
+}
+
+func (b *body) Content(schema *zcl.BodySchema) (*zcl.BodyContent, zcl.Diagnostics) {
+	// TODO: Implement
+	return nil, nil
+}
+
+func (b *body) PartialContent(schema *zcl.BodySchema) (*zcl.BodyContent, zcl.Body, zcl.Diagnostics) {
+	// TODO: Implement
+	return nil, nil, nil
+}