json: beginnings of parser

Only supports parsing objects right now, and even then doesn't really
because objects have to contain strings and that isn't implemented yet.

zcl/json/parser.go

@@ -0,0 +1,184 @@
+package json
+
+import (
+	"github.com/apparentlymart/go-zcl/zcl"
+)
+
+func parseFileContent(buf []byte, filename string) (node, zcl.Diagnostics) {
+	tokens := scan(buf, pos{
+		Filename: filename,
+		Pos: zcl.Pos{
+			Byte:   0,
+			Line:   1,
+			Column: 1,
+		},
+	})
+	p := newPeeker(tokens)
+	return parseValue(p)
+}
+
+func parseValue(p *peeker) (node, zcl.Diagnostics) {
+	tok := p.Peek()
+
+	switch tok.Type {
+	case tokenBraceO:
+		return parseObject(p)
+	case tokenBrackO:
+		return parseArray(p)
+	case tokenNumber:
+		return parseNumber(p)
+	case tokenString:
+		return parseString(p)
+	case tokenKeyword:
+		return parseKeyword(p)
+	case tokenBraceC:
+		return nil, zcl.Diagnostics{
+			{
+				Severity: zcl.DiagError,
+				Summary:  "Missing attribute value",
+				Detail:   "A JSON value must start with a brace, a bracket, a number, a string, or a keyword.",
+				Subject:  &tok.Range,
+			},
+		}
+	case tokenBrackC:
+		return nil, zcl.Diagnostics{
+			{
+				Severity: zcl.DiagError,
+				Summary:  "Missing array element value",
+				Detail:   "A JSON value must start with a brace, a bracket, a number, a string, or a keyword.",
+				Subject:  &tok.Range,
+			},
+		}
+	default:
+		return nil, zcl.Diagnostics{
+			{
+				Severity: zcl.DiagError,
+				Summary:  "Invalid start of value",
+				Detail:   "A JSON value must start with a brace, a bracket, a number, a string, or a keyword.",
+				Subject:  &tok.Range,
+			},
+		}
+	}
+}
+
+func tokenCanStartValue(tok token) bool {
+	switch tok.Type {
+	case tokenBraceO, tokenBrackO, tokenNumber, tokenString, tokenKeyword:
+		return true
+	default:
+		return false
+	}
+}
+
+func parseObject(p *peeker) (node, zcl.Diagnostics) {
+	var diags zcl.Diagnostics
+
+	open := p.Read()
+	attrs := map[string]*objectAttr{}
+
+Token:
+	for {
+		if p.Peek().Type == tokenBraceC {
+			break Token
+		}
+
+		keyNode, keyDiags := parseValue(p)
+		diags = diags.Extend(keyDiags)
+		if keyNode == nil {
+			return nil, diags
+		}
+
+		keyStrNode, ok := keyNode.(*stringVal)
+		if !ok {
+			return nil, diags.Append(&zcl.Diagnostic{
+				Severity: zcl.DiagError,
+				Summary:  "Invalid object attribute name",
+				Detail:   "A JSON object attribute name must be a string",
+				Subject:  keyNode.StartRange().Ptr(),
+			})
+		}
+
+		key := keyStrNode.Value
+
+		colon := p.Read()
+		if colon.Type != tokenComma {
+			if colon.Type == tokenBraceC || colon.Type == tokenComma {
+				// Catch common mistake of using braces instead of brackets
+				// for an array.
+				return nil, diags.Append(&zcl.Diagnostic{
+					Severity: zcl.DiagError,
+					Summary:  "Missing object value",
+					Detail:   "A JSON object attribute must have a value, introduced by a colon.",
+					Subject:  &colon.Range,
+				})
+			}
+
+			return nil, diags.Append(&zcl.Diagnostic{
+				Severity: zcl.DiagError,
+				Summary:  "Missing attribute value colon",
+				Detail:   "A colon must appear between an object attribute's name and its value.",
+				Subject:  &colon.Range,
+			})
+		}
+
+		valNode, valDiags := parseValue(p)
+		diags = diags.Extend(valDiags)
+		if keyNode == nil {
+			return nil, diags
+		}
+
+		attrs[key] = &objectAttr{
+			Name:      key,
+			Value:     valNode,
+			NameRange: keyStrNode.SrcRange,
+		}
+
+		switch p.Peek().Type {
+		case tokenComma:
+			p.Read()
+			if p.Peek().Type == tokenBraceC {
+				// Special error message for this common mistake
+				return nil, diags.Append(&zcl.Diagnostic{
+					Severity: zcl.DiagError,
+					Summary:  "Trailing comma in object",
+					Detail:   "JSON does not permit a trailing comma after the final attribute in an object.",
+					Subject:  &colon.Range,
+				})
+			}
+			continue Token
+		case tokenBraceC:
+			break Token
+		default:
+			return nil, diags.Append(&zcl.Diagnostic{
+				Severity: zcl.DiagError,
+				Summary:  "Missing attribute seperator comma",
+				Detail:   "A comma must appear between each attribute declaration in an object.",
+				Subject:  &colon.Range,
+			})
+		}
+
+	}
+
+	close := p.Read()
+	return &objectVal{
+		Attrs:     attrs,
+		SrcRange:  zcl.RangeBetween(open.Range, close.Range),
+		OpenRange: open.Range,
+	}, diags
+}
+
+func parseArray(p *peeker) (node, zcl.Diagnostics) {
+	return nil, nil
+}
+
+func parseNumber(p *peeker) (node, zcl.Diagnostics) {
+	return nil, nil
+}
+
+func parseString(p *peeker) (node, zcl.Diagnostics) {
+	return nil, nil
+}
+
+func parseKeyword(p *peeker) (node, zcl.Diagnostics) {
+	return nil, nil
+}