shader: Bug fix: true/false should be available as a local variable

internal/shader/expr.go

@@ -369,14 +369,6 @@ func (cs *compileState) parseExpr(block *block, expr ast.Expr) ([]shaderir.Expr,
 		return exprs, f.ir.OutParams, stmts, true
 
 	case *ast.Ident:
-		if e.Name == "true" || e.Name == "false" {
-			return []shaderir.Expr{
-				{
-					Type:  shaderir.NumberExpr,
-					Const: gconstant.MakeBool(e.Name == "true"),
-				},
-			}, []shaderir.Type{{Main: shaderir.Bool}}, nil, true
-		}
 		if e.Name == "_" {
 			return []shaderir.Expr{
 				{
@@ -425,6 +417,14 @@ func (cs *compileState) parseExpr(block *block, expr ast.Expr) ([]shaderir.Expr,
 				},
 			}, nil, nil, true
 		}
+		if e.Name == "true" || e.Name == "false" {
+			return []shaderir.Expr{
+				{
+					Type:  shaderir.NumberExpr,
+					Const: gconstant.MakeBool(e.Name == "true"),
+				},
+			}, []shaderir.Type{{Main: shaderir.Bool}}, nil, true
+		}
 		cs.addError(e.Pos(), fmt.Sprintf("unexpected identifier: %s", e.Name))
 
 	case *ast.ParenExpr:

shader_test.go

@@ -506,3 +506,15 @@ func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
 		t.Errorf("error must be non-nil but was nil")
 	}
 }
+
+func TestShaderBoolLiteral(t *testing.T) {
+	if _, err := NewShader([]byte(`package main
+
+func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
+	true := vec4(0)
+	return true
+}
+`)); err != nil {
+		t.Errorf("error must be nil but was non-nil")
+	}
+}