Fix stack overflow caused by circular destructuring (#2542)

Author: ahejlsberg

internal/checker/checker.go

@@ -13326,6 +13326,7 @@ func (c *Checker) getNarrowedTypeOfSymbol(symbol *ast.Symbol, location *ast.Node
 	t := c.getTypeOfSymbol(symbol)
 	declaration := symbol.ValueDeclaration
 	if declaration != nil {
+		switch {
 		// If we have a non-rest binding element with no initializer declared as a const variable or a const-like
 		// parameter (a parameter for which there are no assignments in the function body), and if the parent type
 		// for the destructuring is a union type, one or more of the binding elements may represent discriminant
@@ -13349,7 +13350,7 @@ func (c *Checker) getNarrowedTypeOfSymbol(symbol *ast.Symbol, location *ast.Node
 		// the binding pattern AST instance for '{ kind, payload }' as a pseudo-reference and narrow this reference
 		// as if it occurred in the specified location. We then recompute the narrowed binding element type by
 		// destructuring from the narrowed parent type.
-		if ast.IsBindingElement(declaration) && declaration.Initializer() == nil && !hasDotDotDotToken(declaration) && len(declaration.Parent.Elements()) >= 2 {
+		case ast.IsBindingElement(declaration) && declaration.Initializer() == nil && !hasDotDotDotToken(declaration) && len(declaration.Parent.Elements()) >= 2:
 			parent := declaration.Parent.Parent
 			rootDeclaration := ast.GetRootDeclaration(parent)
 			if ast.IsVariableDeclaration(rootDeclaration) && c.getCombinedNodeFlagsCached(rootDeclaration)&ast.NodeFlagsConstant != 0 || ast.IsParameter(rootDeclaration) {
@@ -13361,21 +13362,21 @@ func (c *Checker) getNarrowedTypeOfSymbol(symbol *ast.Symbol, location *ast.Node
 					if parentType != nil {
 						parentTypeConstraint = c.mapType(parentType, c.getBaseConstraintOrType)
 					}
-					links.flags &^= NodeCheckFlagsInCheckIdentifier
 					if parentTypeConstraint != nil && parentTypeConstraint.flags&TypeFlagsUnion != 0 && !(ast.IsParameter(rootDeclaration) && c.isSomeSymbolAssigned(rootDeclaration)) {
 						pattern := declaration.Parent
 						narrowedType := c.getFlowTypeOfReferenceEx(pattern, parentTypeConstraint, parentTypeConstraint, nil /*flowContainer*/, getFlowNodeOfNode(location))
 						if narrowedType.flags&TypeFlagsNever != 0 {
-							return c.neverType
+							t = c.neverType
+						} else {
+							// Destructurings are validated against the parent type elsewhere. Here we disable tuple bounds
+							// checks because the narrowed type may have lower arity than the full parent type. For example,
+							// for the declaration [x, y]: [1, 2] | [3], we may have narrowed the parent type to just [3].
+							t = c.getBindingElementTypeFromParentType(declaration, narrowedType, true /*noTupleBoundsCheck*/)
 						}
-						// Destructurings are validated against the parent type elsewhere. Here we disable tuple bounds
-						// checks because the narrowed type may have lower arity than the full parent type. For example,
-						// for the declaration [x, y]: [1, 2] | [3], we may have narrowed the parent type to just [3].
-						return c.getBindingElementTypeFromParentType(declaration, narrowedType, true /*noTupleBoundsCheck*/)
 					}
+					links.flags &^= NodeCheckFlagsInCheckIdentifier
 				}
 			}
-		}
 		// If we have a const-like parameter with no type annotation or initializer, and if the parameter is contextually
 		// typed by a signature with a single rest parameter of a union of tuple types, one or more of the parameters may
 		// represent discriminant tuple elements, and we want the effects of conditional checks on such discriminants to
@@ -13396,7 +13397,7 @@ func (c *Checker) getNarrowedTypeOfSymbol(symbol *ast.Symbol, location *ast.Node
 		// the arrow function AST node for '(kind, payload) => ...' as a pseudo-reference and narrow this reference as
 		// if it occurred in the specified location. We then recompute the narrowed parameter type by indexing into the
 		// narrowed tuple type.
-		if ast.IsParameter(declaration) && declaration.Type() == nil && declaration.Initializer() == nil && !hasDotDotDotToken(declaration) {
+		case ast.IsParameter(declaration) && declaration.Type() == nil && declaration.Initializer() == nil && !hasDotDotDotToken(declaration):
 			fn := declaration.Parent
 			if len(fn.Parameters()) >= 2 && c.isContextSensitiveFunctionOrObjectLiteralMethod(fn) {
 				contextualSignature := c.getContextualSignature(fn)
@@ -13410,7 +13411,7 @@ func (c *Checker) getNarrowedTypeOfSymbol(symbol *ast.Symbol, location *ast.Node
 					if restType.flags&TypeFlagsUnion != 0 && everyType(restType, isTupleType) && !core.Some(fn.Parameters(), c.isSomeSymbolAssigned) {
 						narrowedType := c.getFlowTypeOfReferenceEx(fn, restType, restType, nil /*flowContainer*/, getFlowNodeOfNode(location))
 						index := slices.Index(fn.Parameters(), declaration) - (core.IfElse(ast.GetThisParameter(fn) != nil, 1, 0))
-						return c.getIndexedAccessType(narrowedType, c.getNumberLiteralType(jsnum.Number(index)))
+						t = c.getIndexedAccessType(narrowedType, c.getNumberLiteralType(jsnum.Number(index)))
 					}
 				}
 			}

testdata/baselines/reference/compiler/circularDestructuring.errors.txt

@@ -0,0 +1,21 @@
+circularDestructuring.ts(1,7): error TS2322: Type '{ c: number; f: any; }' is not assignable to type 'string | number'.
+circularDestructuring.ts(1,9): error TS2339: Property 'c' does not exist on type 'string | number'.
+circularDestructuring.ts(1,12): error TS2339: Property 'f' does not exist on type 'string | number'.
+circularDestructuring.ts(1,12): error TS7022: 'f' implicitly has type 'any' because it does not have a type annotation and is referenced directly or indirectly in its own initializer.
+circularDestructuring.ts(1,43): error TS2448: Block-scoped variable 'f' used before its declaration.
+
+
+==== circularDestructuring.ts (5 errors) ====
+    const { c, f }: string | number = { c: 0, f };
+          ~~~~~~~~
+!!! error TS2322: Type '{ c: number; f: any; }' is not assignable to type 'string | number'.
+            ~
+!!! error TS2339: Property 'c' does not exist on type 'string | number'.
+               ~
+!!! error TS2339: Property 'f' does not exist on type 'string | number'.
+               ~
+!!! error TS7022: 'f' implicitly has type 'any' because it does not have a type annotation and is referenced directly or indirectly in its own initializer.
+                                              ~
+!!! error TS2448: Block-scoped variable 'f' used before its declaration.
+!!! related TS2728 circularDestructuring.ts:1:12: 'f' is declared here.
+    

testdata/baselines/reference/compiler/circularDestructuring.symbols

@@ -0,0 +1,9 @@
+//// [tests/cases/compiler/circularDestructuring.ts] ////
+
+=== circularDestructuring.ts ===
+const { c, f }: string | number = { c: 0, f };
+>c : Symbol(c, Decl(circularDestructuring.ts, 0, 7))
+>f : Symbol(f, Decl(circularDestructuring.ts, 0, 10))
+>c : Symbol(c, Decl(circularDestructuring.ts, 0, 35))
+>f : Symbol(f, Decl(circularDestructuring.ts, 0, 41))
+

testdata/baselines/reference/compiler/circularDestructuring.types

@@ -0,0 +1,11 @@
+//// [tests/cases/compiler/circularDestructuring.ts] ////
+
+=== circularDestructuring.ts ===
+const { c, f }: string | number = { c: 0, f };
+>c : any
+>f : any
+>{ c: 0, f } : { c: number; f: any; }
+>c : number
+>0 : 0
+>f : any
+

testdata/tests/cases/compiler/circularDestructuring.ts

@@ -0,0 +1,3 @@
+// @strict: true
+// @noEmit: true
+const { c, f }: string | number = { c: 0, f };