fix(gnovm): prevent cyclic references in type declarations (#2081)

Address #2008.


In this pull request, we're implementing a special handling for type
declarations to check cynic dependency. Due to their unique nature, we
must meticulously search through their fields to identify potential
cyclic reference.

<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
- [ ] Added new benchmarks to [generated
graphs](https://gnoland.github.io/benchmarks), if any. More info
[here](https://github.com/gnolang/gno/blob/master/.benchmarks/README.md).
</details>

---------

Co-authored-by: deelawn <dboltz03@gmail.com>

gnovm/pkg/gnolang/preprocess.go

@@ -2906,6 +2906,92 @@ func convertConst(store Store, last BlockNode, cx *ConstExpr, t Type) {
 	}
 }
 
+func assertTypeDeclNoCycle(store Store, last BlockNode, td *TypeDecl, stack *[]Name) {
+	assertTypeDeclNoCycle2(store, last, td.Type, stack, false, td.IsAlias)
+}
+
+func assertTypeDeclNoCycle2(store Store, last BlockNode, x Expr, stack *[]Name, indirect bool, isAlias bool) {
+	if x == nil {
+		panic("unexpected nil expression when checking for type declaration cycles")
+	}
+
+	var lastX Expr
+	defer func() {
+		if _, ok := lastX.(*NameExpr); ok {
+			// pop stack
+			*stack = (*stack)[:len(*stack)-1]
+		}
+	}()
+
+	switch cx := x.(type) {
+	case *NameExpr:
+		var msg string
+
+		// Function to build the error message
+		buildMessage := func() string {
+			for j := 0; j < len(*stack); j++ {
+				msg += fmt.Sprintf("%s -> ", (*stack)[j])
+			}
+			return msg + string(cx.Name) // Append the current name last
+		}
+
+		// Check for existence of cx.Name in stack
+		findCycle := func() {
+			for _, n := range *stack {
+				if n == cx.Name {
+					msg = buildMessage()
+					panic(fmt.Sprintf("invalid recursive type: %s", msg))
+				}
+			}
+		}
+
+		if indirect && !isAlias {
+			*stack = (*stack)[:0]
+		} else {
+			findCycle()
+			*stack = append(*stack, cx.Name)
+			lastX = cx
+		}
+
+		return
+	case *SelectorExpr:
+		assertTypeDeclNoCycle2(store, last, cx.X, stack, indirect, isAlias)
+	case *StarExpr:
+		assertTypeDeclNoCycle2(store, last, cx.X, stack, true, isAlias)
+	case *FieldTypeExpr:
+		assertTypeDeclNoCycle2(store, last, cx.Type, stack, indirect, isAlias)
+	case *ArrayTypeExpr:
+		if cx.Len != nil {
+			assertTypeDeclNoCycle2(store, last, cx.Len, stack, indirect, isAlias)
+		}
+		assertTypeDeclNoCycle2(store, last, cx.Elt, stack, indirect, isAlias)
+	case *SliceTypeExpr:
+		assertTypeDeclNoCycle2(store, last, cx.Elt, stack, true, isAlias)
+	case *InterfaceTypeExpr:
+		for i := range cx.Methods {
+			assertTypeDeclNoCycle2(store, last, &cx.Methods[i], stack, indirect, isAlias)
+		}
+	case *ChanTypeExpr:
+		assertTypeDeclNoCycle2(store, last, cx.Value, stack, true, isAlias)
+	case *FuncTypeExpr:
+		for i := range cx.Params {
+			assertTypeDeclNoCycle2(store, last, &cx.Params[i], stack, true, isAlias)
+		}
+		for i := range cx.Results {
+			assertTypeDeclNoCycle2(store, last, &cx.Results[i], stack, true, isAlias)
+		}
+	case *MapTypeExpr:
+		assertTypeDeclNoCycle2(store, last, cx.Key, stack, true, isAlias)
+		assertTypeDeclNoCycle2(store, last, cx.Value, stack, true, isAlias)
+	case *StructTypeExpr:
+		for i := range cx.Fields {
+			assertTypeDeclNoCycle2(store, last, &cx.Fields[i], stack, indirect, isAlias)
+		}
+	default:
+	}
+	return
+}
+
 // Returns any names not yet defined nor predefined in expr.  These happen
 // upon transcribe:enter from the top, so value paths cannot be used.  If no
 // names are un and x is TypeExpr, evalStaticType(store,last, x) must not
@@ -3197,27 +3283,36 @@ func predefineNow(store Store, last BlockNode, d Decl) (Decl, bool) {
 			}
 		}
 	}()
-	m := make(map[Name]struct{})
-	return predefineNow2(store, last, d, m)
+	stack := &[]Name{}
+	return predefineNow2(store, last, d, stack)
 }
 
-func predefineNow2(store Store, last BlockNode, d Decl, m map[Name]struct{}) (Decl, bool) {
+func predefineNow2(store Store, last BlockNode, d Decl, stack *[]Name) (Decl, bool) {
 	pkg := packageOf(last)
 	// pre-register d.GetName() to detect circular definition.
 	for _, dn := range d.GetDeclNames() {
 		if isUverseName(dn) {
 			panic(fmt.Sprintf(
 				"builtin identifiers cannot be shadowed: %s", dn))
 		}
-		m[dn] = struct{}{}
+		*stack = append(*stack, dn)
+	}
+
+	// check type decl cycle
+	if td, ok := d.(*TypeDecl); ok {
+		// recursively check
+		assertTypeDeclNoCycle(store, last, td, stack)
 	}
+
 	// recursively predefine dependencies.
 	for {
 		un := tryPredefine(store, last, d)
 		if un != "" {
 			// check circularity.
-			if _, ok := m[un]; ok {
-				panic(fmt.Sprintf("constant definition loop with %s", un))
+			for _, n := range *stack {
+				if n == un {
+					panic(fmt.Sprintf("constant definition loop with %s", un))
+				}
 			}
 			// look up dependency declaration from fileset.
 			file, decl := pkg.FileSet.GetDeclFor(un)
@@ -3226,7 +3321,7 @@ func predefineNow2(store Store, last BlockNode, d Decl, m map[Name]struct{}) (De
 				panic("all types from files in file-set should have already been predefined")
 			}
 			// predefine dependency (recursive).
-			*decl, _ = predefineNow2(store, file, *decl, m)
+			*decl, _ = predefineNow2(store, file, *decl, stack)
 		} else {
 			break
 		}

gnovm/tests/files/circular_constant.gno

@@ -0,0 +1,10 @@
+package main
+
+const A = B
+const B = A + 1
+
+func main() {
+}
+
+// Error:
+// main/files/circular_constant.gno:3:7: constant definition loop with A

gnovm/tests/files/recursive1.gno

@@ -0,0 +1,13 @@
+package main
+
+type S struct {
+	T S
+}
+
+func main() {
+	var a, b S
+	println(a == b)
+}
+
+// Error:
+// main/files/recursive1.gno:1:1: invalid recursive type: S -> S

gnovm/tests/files/recursive1a.gno

@@ -0,0 +1,15 @@
+package main
+
+type S1 *S
+
+type S struct {
+	T S1
+}
+
+func main() {
+	var a, b S
+	println(a == b)
+}
+
+// Output:
+// true

gnovm/tests/files/recursive1b.gno

@@ -0,0 +1,16 @@
+package main
+
+type S struct {
+	T *S
+	B Integer
+}
+
+type Integer int
+
+func main() {
+	var a, b S
+	println(a == b)
+}
+
+// Output:
+// true

gnovm/tests/files/recursive1c.gno

@@ -0,0 +1,17 @@
+package main
+
+import "fmt"
+
+type S struct {
+	A [2][2]S
+}
+
+func main() {
+	var a, b S
+
+	fmt.Println(a)
+	fmt.Println(b)
+}
+
+// Error:
+// main/files/recursive1c.gno:1:1: invalid recursive type: S -> S

gnovm/tests/files/recursive1d.gno

@@ -0,0 +1,17 @@
+package main
+
+import "fmt"
+
+type S struct {
+	A [2]S
+}
+
+func main() {
+	var a, b S
+
+	fmt.Println(a)
+	fmt.Println(b)
+}
+
+// Error:
+// main/files/recursive1d.gno:1:1: invalid recursive type: S -> S

gnovm/tests/files/recursive1e.gno

@@ -0,0 +1,13 @@
+package main
+
+type S struct {
+	A [2][]S
+}
+
+func main() {
+	var a, b S
+	println(a)
+}
+
+// Output:
+// (struct{(array[(nil []main.S),(nil []main.S)] [2][]main.S)} main.S)

gnovm/tests/files/recursive1f.gno

@@ -0,0 +1,13 @@
+package main
+
+func main() {
+	type S struct {
+		T S
+	}
+
+	var a, b S
+	println(a == b)
+}
+
+// Error:
+// main/files/recursive1f.gno:3:1: invalid recursive type: S -> S

gnovm/tests/files/recursive2.gno

@@ -0,0 +1,21 @@
+package main
+
+type A struct {
+	X B
+}
+
+type B struct {
+	X C
+}
+
+type C struct {
+	X A
+}
+
+func main() {
+	var p, q A
+	println(p == q)
+}
+
+// Error:
+// main/files/recursive2.gno:1:1: invalid recursive type: A -> B -> C -> A

gnovm/tests/files/recursive2a.gno

@@ -0,0 +1,21 @@
+package main
+
+type A struct {
+	X B
+}
+
+type B struct {
+	X int
+}
+
+type C struct {
+	X A
+}
+
+func main() {
+	var p, q A
+	println(p == q)
+}
+
+// Output:
+// true

gnovm/tests/files/recursive2b.gno

@@ -0,0 +1,21 @@
+package main
+
+type A struct {
+	X B
+}
+
+type B struct {
+	X C
+}
+
+type C struct {
+	X *A
+}
+
+func main() {
+	var p, q A
+	println(p == q)
+}
+
+// Output:
+// true

gnovm/tests/files/recursive2c.gno

@@ -0,0 +1,21 @@
+package main
+
+func main() {
+	type A struct {
+		X B
+	}
+
+	type B struct {
+		X C
+	}
+
+	type C struct {
+		X A
+	}
+
+	var p, q A
+	println(p == q)
+}
+
+// Error:
+// main/files/recursive2c.gno:3:1: name B not defined in fileset with files [files/recursive2c.gno]

gnovm/tests/files/recursive2d.gno

@@ -0,0 +1,21 @@
+package main
+
+type A struct {
+	X *B
+}
+
+type B struct {
+	X int
+}
+
+type C struct {
+	X A
+}
+
+func main() {
+	var p, q A
+	println(p == q)
+}
+
+// Output:
+// true

gnovm/tests/files/recursive3.gno

@@ -0,0 +1,13 @@
+package main
+
+type S struct {
+	T *S
+}
+
+func main() {
+	var a, b S
+	println(a == b)
+}
+
+// Output:
+// true