fix(tolk/type-inference): correctly handle cyclic structs (#133)

Fixes #132

Author: i582

server/src/e2e/tolk/testcases/types/basic.test

@@ -394,3 +394,23 @@ fun main() {
 }
 ------------------------------------------------------------------------
 ok
+
+========================================================================
+Cyclic dependency with Cell in struct
+========================================================================
+struct SwapStep {
+    pool: address
+    minAmountOut: coins
+    nextStep: Cell<SwapStep>?
+}
+
+fun main() {
+    val foo = SwapStep{};
+//!     ^ SwapStep
+    val step = foo.nextStep!
+//!     ^ Cell<SwapStep>
+    val loadedStep = foo.nextStep!.load()
+//!     ^ SwapStep
+}
+------------------------------------------------------------------------
+ok

server/src/languages/tolk/TypeInferer.ts

@@ -670,11 +670,16 @@ export class TypeInferer {
 
     private inferTypeFromResolved(resolved: NamedNode): Ty | null {
         if (resolved instanceof Struct) {
-            const baseTy = new StructTy(
-                resolved.fields().map(it => this.inferType(it.typeNode()) ?? UnknownTy.UNKNOWN),
-                resolved.name(),
-                resolved,
-            )
+            const fieldTypes = resolved.fields().map(it => {
+                try {
+                    return this.inferType(it.typeNode()) ?? UnknownTy.UNKNOWN
+                } catch {
+                    // cyclic dependency
+                    return UnknownTy.UNKNOWN
+                }
+            })
+
+            const baseTy = new StructTy(fieldTypes, resolved.name(), resolved)
 
             const typeParameters = resolved.typeParameters()
             if (typeParameters.length > 0) {