Detect recursive types early

src/ast.ts

@@ -834,6 +834,9 @@ export abstract class TypeNode extends Node {
     super(kind, range);
   }
 
+  /** Whether this type node is currently in the process of being resolved. */
+  currentlyResolving: bool = false;
+
   /** Tests if this type has a generic component matching one of the given type parameters. */
   hasGenericComponent(typeParameterNodes: TypeParameterNode[]): bool {
     if (this.kind == NodeKind.NamedType) {

src/parser.ts

@@ -3519,40 +3519,6 @@ export class Parser extends DiagnosticEmitter {
     return null;
   }
 
-  private getRecursiveDepthForTypeDeclaration(
-    identifierName: string,
-    type: TypeNode,
-    depth: i32 = 0
-  ): i32 {
-    switch (type.kind) {
-      case NodeKind.NamedType: {
-        let typeArguments = (<NamedTypeNode>type).typeArguments;
-        if (typeArguments) {
-          for (let i = 0, k = typeArguments.length; i < k; i++) {
-            let res = this.getRecursiveDepthForTypeDeclaration(identifierName, typeArguments[i], depth + 1);
-            if (res != -1) return res;
-          }
-        }
-        if ((<NamedTypeNode>type).name.identifier.text == identifierName) {
-          return depth;
-        }
-        break;
-      }
-      case NodeKind.FunctionType: {
-        let fnType = <FunctionTypeNode>type;
-        let res = this.getRecursiveDepthForTypeDeclaration(identifierName, fnType.returnType, depth + 1);
-        if (res != -1) return res;
-        let params = fnType.parameters;
-        for (let i = 0, k = params.length; i < k; i++) {
-          res = this.getRecursiveDepthForTypeDeclaration(identifierName, params[i].type, depth + 1);
-          if (res != -1) return res;
-        }
-        break;
-      }
-    }
-    return -1;
-  }
-
   parseTypeDeclaration(
     tn: Tokenizer,
     flags: CommonFlags,
@@ -3574,19 +3540,11 @@ export class Parser extends DiagnosticEmitter {
         tn.skip(Token.Bar);
         let type = this.parseType(tn);
         if (!type) return null;
-        let depth = this.getRecursiveDepthForTypeDeclaration(name.text, type);
-        if (depth >= 0) {
-          if (depth == 0) {
-            this.error(
-              DiagnosticCode.Type_alias_0_circularly_references_itself,
-              tn.range(), name.text
-            );
-          } else {
-            this.error(
-              DiagnosticCode.Not_implemented_0,
-              tn.range(), "Recursion in type aliases"
-            );
-          }
+        if (isCircularTypeAlias(name.text, type)) {
+          this.error(
+            DiagnosticCode.Type_alias_0_circularly_references_itself,
+            name.range, name.text
+          );
           return null;
         }
         let ret = Node.createTypeDeclaration(
@@ -4593,3 +4551,32 @@ function determinePrecedence(kind: Token): Precedence {
   }
   return Precedence.None;
 }
+
+/** Checks if the type alias of the given name and type is circular. */
+function isCircularTypeAlias(name: string, type: TypeNode): bool {
+  switch (type.kind) {
+    case NodeKind.NamedType: {
+      if ((<NamedTypeNode>type).name.identifier.text == name) {
+        return true;
+      }
+      let typeArguments = (<NamedTypeNode>type).typeArguments;
+      if (typeArguments) {
+        for (let i = 0, k = typeArguments.length; i < k; i++) {
+          if (isCircularTypeAlias(name, typeArguments[i])) return true;
+        }
+      }
+      break;
+    }
+    case NodeKind.FunctionType: {
+      let functionType = <FunctionTypeNode>type;
+      if (isCircularTypeAlias(name, functionType.returnType)) return true;
+      let parameters = functionType.parameters;
+      for (let i = 0, k = parameters.length; i < k; i++) {
+        if (isCircularTypeAlias(name, parameters[i].type)) return true;
+      }
+      break;
+    }
+    default: assert(false);
+  }
+  return false;
+}

src/resolver.ts

@@ -149,26 +149,38 @@ export class Resolver extends DiagnosticEmitter {
     /** How to proceed with eventual diagnostics. */
     reportMode: ReportMode = ReportMode.Report
   ): Type | null {
+    if (node.currentlyResolving) {
+      this.error(
+        DiagnosticCode.Not_implemented_0,
+        node.range, "Recursive types"
+      );
+      return null;
+    }
+    node.currentlyResolving = true;
+    let resolved: Type | null = null;
     switch (node.kind) {
       case NodeKind.NamedType: {
-        return this.resolveNamedType(
+        resolved = this.resolveNamedType(
           <NamedTypeNode>node,
           ctxElement,
           ctxTypes,
           reportMode
         );
+        break;
       }
       case NodeKind.FunctionType: {
-        return this.resolveFunctionType(
+        resolved = this.resolveFunctionType(
           <FunctionTypeNode>node,
           ctxElement,
           ctxTypes,
           reportMode
         );
+        break;
       }
       default: assert(false);
     }
-    return null;
+    node.currentlyResolving = false;
+    return resolved;
   }
 
   /** Resolves a {@link NamedTypeNode} to a concrete {@link Type}. */
@@ -2721,7 +2733,7 @@ export class Resolver extends DiagnosticEmitter {
     const declaration = node.declaration;
     const signature = declaration.signature;
     const body = declaration.body;
-    let functionType = this.resolveFunctionType(signature, ctxFlow.sourceFunction, ctxFlow.contextualTypeArguments, reportMode);
+    let functionType = this.resolveType(signature, ctxFlow.sourceFunction, ctxFlow.contextualTypeArguments, reportMode);
     if (
       functionType &&
       declaration.arrowKind != ArrowKind.None &&

tests/compiler/typerecursion.json

@@ -0,0 +1,6 @@
+{
+  "stderr": [
+    "AS100: Not implemented: Recursive types",
+    "EOF"
+  ]
+}

tests/compiler/typerecursion.ts

@@ -0,0 +1,6 @@
+type RecMethod = () => RecReturn;
+type RecReturn = RecMethod | null;
+
+const test: RecMethod = () => null;
+
+ERROR("EOF");

tests/parser/type.ts.fixture.ts

@@ -5,11 +5,11 @@ export type T1 = int32_t;
 export type T2 = int32_t;
 export type T11 = T1 | null;
 export type T12 = T1 | null;
-// ERROR 2456: "Type alias 'T3' circularly references itself." in type.ts(11,23+4)
-// ERROR 100: "Not implemented: Recursion in type aliases" in type.ts(12,29+3)
-// ERROR 100: "Not implemented: Recursion in type aliases" in type.ts(13,24+2)
-// ERROR 100: "Not implemented: Recursion in type aliases" in type.ts(14,31+1)
-// ERROR 100: "Not implemented: Recursion in type aliases" in type.ts(15,26+1)
-// ERROR 100: "Not implemented: Recursion in type aliases" in type.ts(16,39+1)
-// ERROR 100: "Not implemented: Recursion in type aliases" in type.ts(17,32+1)
-// ERROR 100: "Not implemented: Recursion in type aliases" in type.ts(18,25+1)
+// ERROR 2456: "Type alias 'T3' circularly references itself." in type.ts(11,13+2)
+// ERROR 2456: "Type alias 'T4' circularly references itself." in type.ts(12,13+2)
+// ERROR 2456: "Type alias 'T5' circularly references itself." in type.ts(13,13+2)
+// ERROR 2456: "Type alias 'T6' circularly references itself." in type.ts(14,13+2)
+// ERROR 2456: "Type alias 'T7' circularly references itself." in type.ts(15,13+2)
+// ERROR 2456: "Type alias 'T8' circularly references itself." in type.ts(16,13+2)
+// ERROR 2456: "Type alias 'T9' circularly references itself." in type.ts(17,13+2)
+// ERROR 2456: "Type alias 'T10' circularly references itself." in type.ts(18,13+3)