fix: missing length check in value declaration

gnovm/pkg/gnolang/preprocess.go

@@ -438,8 +438,12 @@ func Preprocess(store Store, ctx BlockNode, n Node) Node {
 					// skip declarations already predefined
 					// (e.g. through recursion for a dependent)
 				} else {
+					d := n.(Decl)
+					if cd, ok := d.(*ValueDecl); ok {
+						checkAssignmentMismatch(cd)
+					}
 					// recursively predefine dependencies.
-					d2, ppd := predefineNow(store, last, n.(Decl))
+					d2, ppd := predefineNow(store, last, d)
 					if ppd {
 						return d2, TRANS_SKIP
 					} else {
@@ -2062,8 +2066,8 @@ func Preprocess(store Store, ctx BlockNode, n Node) Node {
 					// special case if `var a, b, c T? = f()` form.
 					cx := n.Values[0].(*CallExpr)
 					tt := evalStaticTypeOfRaw(store, last, cx).(*tupleType)
-					if len(tt.Elts) != numNames {
-						panic("should not happen")
+					if rLen := len(tt.Elts); rLen != numNames {
+						panic(fmt.Sprintf("assignment mismatch: %d variable(s) but %s returns %d value(s)", numNames, cx.Func.String(), rLen))
 					}
 					if n.Type != nil {
 						// only a single type can be specified.
@@ -2084,6 +2088,14 @@ func Preprocess(store Store, ctx BlockNode, n Node) Node {
 				} else if len(n.Values) != 0 && numNames != len(n.Values) {
 					panic("should not happen")
 				} else { // general case
+					for _, v := range n.Values {
+						if cx, ok := v.(*CallExpr); ok {
+							tt, ok := evalStaticTypeOfRaw(store, last, cx).(*tupleType)
+							if ok && len(tt.Elts) != 1 {
+								panic(fmt.Sprintf("multiple-value %s (value of type %s) in single-value context", cx.Func.String(), tt.Elts))
+							}
+						}
+					}
 					// evaluate types and convert consts.
 					if n.Type != nil {
 						// only a single type can be specified.
@@ -3051,6 +3063,20 @@ func checkIntegerKind(xt Type) {
 	}
 }
 
+func checkAssignmentMismatch(cd *ValueDecl) {
+	var (
+		numNames  = len(cd.NameExprs)
+		numValues = len(cd.Values)
+	)
+	if numValues <= 0 || numValues == numNames {
+		return
+	}
+
+	if _, ok := cd.Values[0].(*CallExpr); !ok {
+		panic(fmt.Sprintf("assignment mismatch: %d variable(s) but %d value(s)", numNames, numValues))
+	}
+}
+
 // predefineNow() pre-defines (with empty placeholders) all
 // declaration names, and then preprocesses all type/value decls, and
 // partially processes func decls.

gnovm/tests/files/var18.gno

@@ -1,8 +1,8 @@
 package main
 
 func main() {
-	a, b, c := 1, 2
+	var a, b, c = 1, 2
 }
 
 // Error:
-// main/files/var18.gno:4:2: assignment mismatch: 3 variables but 2 values
+// main/files/var18.gno:4:6: assignment mismatch: 3 variable(s) but 2 value(s)

gnovm/tests/files/var19.gno

@@ -0,0 +1,11 @@
+package main
+
+func main() {
+	var a, b, c = 1, a+1
+	println(a)
+	println(b)
+	println(c)
+}
+
+// Error:
+// main/files/var19.gno:4:6: assignment mismatch: 3 variable(s) but 2 value(s)

gnovm/tests/files/var20.gno

@@ -0,0 +1,12 @@
+package main
+
+func r() int {
+	return 1
+}
+
+func main() {
+	var a, b, c = r()
+}
+
+// Error:
+// main/files/var20.gno:8:6: assignment mismatch: 3 variable(s) but r<VPBlock(3,0)> returns 1 value(s)

gnovm/tests/files/var21.gno

@@ -0,0 +1,14 @@
+package main
+
+func foo() (int, bool) {
+	return 1, true
+}
+
+func main() {
+	var a, b = 2, foo()
+
+	println(a, b)
+}
+
+// Error:
+// main/files/var21.gno:8:6: multiple-value foo<VPBlock(3,0)> (value of type [int bool]) in single-value context

gnovm/tests/files/var22.gno

@@ -0,0 +1,14 @@
+package main
+
+func foo() (int, bool) {
+	return 1, true
+}
+
+func main() {
+	var a, b, c = 2, foo()
+
+	println(a, b, c)
+}
+
+// Error:
+// main/files/var22.gno:8:6: assignment mismatch: 3 variable(s) but 2 value(s)