check JSON value in string literal passed to fromJSON

Author: rhysd

expr_sema.go

@@ -1,6 +1,7 @@
 package actionlint
 
 import (
+	"encoding/json"
 	"fmt"
 	"regexp"
 	"strconv"
@@ -786,15 +787,15 @@ func checkFuncSignature(n *FuncCallNode, sig *FuncSignature, args []ExprType) *E
 	return nil
 }
 
-func (sema *ExprSemanticsChecker) checkBuiltinFunctionCall(n *FuncCallNode, _ *FuncSignature) {
+func (sema *ExprSemanticsChecker) checkBuiltinFuncCall(n *FuncCallNode, sig *FuncSignature) ExprType {
 	sema.checkSpecialFunctionAvailability(n)
 
 	// Special checks for specific built-in functions
 	switch strings.ToLower(n.Callee) {
 	case "format":
 		lit, ok := n.Args[0].(*StringNode)
 		if !ok {
-			return
+			return sig.Ret
 		}
 		l := len(n.Args) - 1 // -1 means removing first format string argument
 
@@ -817,7 +818,22 @@ func (sema *ExprSemanticsChecker) checkBuiltinFunctionCall(n *FuncCallNode, _ *F
 		for i := range holders {
 			sema.errorf(n, "format string %q contains placeholder {%d} but only %d arguments are given to format", lit.Value, i, l)
 		}
+	case "fromjson":
+		lit, ok := n.Args[0].(*StringNode)
+		if !ok {
+			return sig.Ret
+		}
+		var v any
+		err := json.Unmarshal([]byte(lit.Value), &v)
+		if err == nil {
+			return typeOfJSONValue(v)
+		}
+		if s, ok := err.(*json.SyntaxError); ok {
+			sema.errorf(lit, "broken JSON string is passed to fromJSON() at offset %d: %s", s.Offset, s)
+		}
 	}
+
+	return sig.Ret
 }
 
 func (sema *ExprSemanticsChecker) checkFuncCall(n *FuncCallNode) ExprType {
@@ -844,8 +860,7 @@ func (sema *ExprSemanticsChecker) checkFuncCall(n *FuncCallNode) ExprType {
 		err := checkFuncSignature(n, sig, tys)
 		if err == nil {
 			// When one of overload pass type check, overload was resolved correctly
-			sema.checkBuiltinFunctionCall(n, sig)
-			return sig.Ret
+			return sema.checkBuiltinFuncCall(n, sig)
 		}
 		errs = append(errs, err)
 	}

expr_type.go

@@ -427,3 +427,46 @@ func (ty *ArrayType) DeepCopy() ExprType {
 func EqualTypes(l, r ExprType) bool {
 	return l.Assignable(r) && r.Assignable(l)
 }
+
+func typeOfJSONValue(v any) ExprType {
+	// https://pkg.go.dev/encoding/json#Unmarshal
+	// To unmarshal JSON into an interface value, Unmarshal stores one of these in the interface value:
+	// - bool, for JSON booleans
+	// - float64, for JSON numbers
+	// - string, for JSON strings
+	// - []interface{}, for JSON arrays
+	// - map[string]interface{}, for JSON objects
+	// - nil for JSON null
+	switch v := v.(type) {
+	case bool:
+		return BoolType{}
+	case float64:
+		return NumberType{}
+	case string:
+		return StringType{}
+	case []any:
+		var elem ExprType
+		for _, e := range v {
+			t := typeOfJSONValue(e)
+			if elem == nil {
+				elem = t
+			} else {
+				elem = elem.Merge(t)
+			}
+		}
+		if elem == nil {
+			elem = AnyType{}
+		}
+		return &ArrayType{Elem: elem}
+	case map[string]any:
+		props := make(map[string]ExprType, len(v))
+		for k, v := range v {
+			props[k] = typeOfJSONValue(v)
+		}
+		return NewStrictObjectType(props)
+	case nil:
+		return NullType{}
+	default:
+		panic(v) // Unreachable
+	}
+}