feat(gnovm): returns error like in Golang when assignment with a func…

…tion which does not return any value (gnolang#3049)

This PR aims at resolving this issue:
gnolang#1082

This depends on gnolang#3017 because it
refactored the code to sync the logic/code between AssignStmt vs
ValueDecl.

Related gnolang#2695

<details><summary>Contributors' checklist...</summary>

- [ ] Added new tests, or not needed, or not feasible
- [ ] Provided an example (e.g. screenshot) to aid review or the PR is
self-explanatory
- [ ] Updated the official documentation or not needed
- [ ] No breaking changes were made, or a `BREAKING CHANGE: xxx` message
was included in the description
- [ ] Added references to related issues and PRs
- [ ] Provided any useful hints for running manual tests
</details>

---------

Co-authored-by: hieu.ha <[email protected]>
Co-authored-by: Mikael VALLENET <[email protected]>

gnovm/pkg/gnolang/preprocess.go

@@ -2373,7 +2373,7 @@ func defineOrDecl(
 	sts := make([]Type, numNames) // static types
 	tvs := make([]TypedValue, numNames)
 
-	if numNames > 1 && len(valueExprs) == 1 {
+	if numVals == 1 && numNames > 1 {
 		parseMultipleAssignFromOneExpr(sts, tvs, store, bn, nameExprs, typeExpr, valueExprs[0])
 	} else {
 		parseAssignFromExprList(sts, tvs, store, bn, isConst, nameExprs, typeExpr, valueExprs)
@@ -2410,7 +2410,7 @@ func parseAssignFromExprList(
 	for _, v := range valueExprs {
 		if cx, ok := v.(*CallExpr); ok {
 			tt, ok := evalStaticTypeOfRaw(store, bn, cx).(*tupleType)
-			if ok && len(tt.Elts) != 1 {
+			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))
 			}
 		}
@@ -3132,18 +3132,12 @@ func gnoTypeOf(store Store, t Type) Type {
 // but rather computes the type OF x.
 func evalStaticTypeOf(store Store, last BlockNode, x Expr) Type {
 	t := evalStaticTypeOfRaw(store, last, x)
-	if tt, ok := t.(*tupleType); ok {
-		if len(tt.Elts) != 1 {
-			panic(fmt.Sprintf(
-				"evalStaticTypeOf() only supports *CallExpr with 1 result, got %s",
-				tt.String(),
-			))
-		} else {
-			return tt.Elts[0]
-		}
-	} else {
-		return t
+
+	if tt, ok := t.(*tupleType); ok && len(tt.Elts) == 1 {
+		return tt.Elts[0]
 	}
+
+	return t
 }
 
 // like evalStaticTypeOf() but returns the raw *tupleType for *CallExpr.

gnovm/pkg/gnolang/type_check.go

@@ -1029,6 +1029,14 @@ func assertValidAssignRhs(store Store, last BlockNode, n Node) {
 			tt = evalStaticType(store, last, exp)
 			panic(fmt.Sprintf("%s (type) is not an expression", tt.String()))
 		}
+
+		// Ensures that function used in ValueDecl or AssignStmt must return at least 1 value.
+		if cx, ok := exp.(*CallExpr); ok {
+			tType, ok := tt.(*tupleType)
+			if ok && len(tType.Elts) == 0 {
+				panic(fmt.Sprintf("%s (no value) used as value", cx.Func.String()))
+			}
+		}
 	}
 }
 

gnovm/tests/files/assign37.gno

@@ -0,0 +1,10 @@
+package main
+
+func f() { }
+
+func main() {
+	a := f()
+}
+
+// Error:
+// main/files/assign37.gno:6:2: f<VPBlock(3,0)> (no value) used as value

gnovm/tests/files/assign37b.gno

@@ -0,0 +1,12 @@
+package main
+
+import "fmt"
+
+func f() { }
+
+func main() {
+	a, b := f(), f()
+}
+
+// Error:
+// main/files/assign37b.gno:8:2: f<VPBlock(3,0)> (no value) used as value

gnovm/tests/files/var34.gno

@@ -0,0 +1,10 @@
+package main
+
+func f() {}
+
+func main() {
+	var t = f()
+}
+
+// Error:
+// main/files/var34.gno:6:6: f<VPBlock(3,0)> (no value) used as value

gnovm/tests/files/var34b.gno

@@ -0,0 +1,11 @@
+package main
+
+func f() {}
+
+func main() {
+	var a int
+	a = f()
+}
+
+// Error:
+// main/files/var34b.gno:7:2: f<VPBlock(3,0)> (no value) used as value

gnovm/tests/files/var34c.gno

@@ -0,0 +1,10 @@
+package main
+
+func f() {}
+
+func main() {
+	var a, b int = f(), 1
+}
+
+// Error:
+// main/files/var34c.gno:6:6: f<VPBlock(3,0)> (no value) used as value