zclsyntax: parsing of boolean/null literals and root variable references

zcl/zclsyntax/expression_test.go

@@ -36,6 +36,30 @@ func TestExpressionParseAndValue(t *testing.T) {
 			cty.NumberIntVal(1),
 			1, // Unbalanced parentheses
 		},
+		{
+			`true`,
+			nil,
+			cty.True,
+			0,
+		},
+		{
+			`false`,
+			nil,
+			cty.False,
+			0,
+		},
+		{
+			`null`,
+			nil,
+			cty.NullVal(cty.DynamicPseudoType),
+			0,
+		},
+		{
+			`true true`,
+			nil,
+			cty.True,
+			1, // extra characters after expression
+		},
 	}
 
 	for _, test := range tests {

zcl/zclsyntax/parser.go

@@ -453,6 +453,38 @@ func (p *parser) parseExpressionTerm() (Expression, zcl.Diagnostics) {
 			SrcRange: tok.Range,
 		}, nil
 
+	case TokenIdent:
+		tok := p.Read() // eat identifier token
+
+		name := string(tok.Bytes)
+		switch name {
+		case "true":
+			return &LiteralValueExpr{
+				Val:      cty.True,
+				SrcRange: tok.Range,
+			}, nil
+		case "false":
+			return &LiteralValueExpr{
+				Val:      cty.False,
+				SrcRange: tok.Range,
+			}, nil
+		case "null":
+			return &LiteralValueExpr{
+				Val:      cty.NullVal(cty.DynamicPseudoType),
+				SrcRange: tok.Range,
+			}, nil
+		default:
+			return &ScopeTraversalExpr{
+				Traversal: zcl.Traversal{
+					zcl.TraverseRoot{
+						Name:     name,
+						SrcRange: tok.Range,
+					},
+				},
+				SrcRange: tok.Range,
+			}, nil
+		}
+
 	default:
 		var diags zcl.Diagnostics
 		if !p.recovery {