Reflect effects of assertion calls in control flow analysis

Author: ahejlsberg

src/compiler/binder.ts

@@ -706,6 +706,9 @@ namespace ts {
                 case SyntaxKind.CaseClause:
                     bindCaseClause(<CaseClause>node);
                     break;
+                case SyntaxKind.ExpressionStatement:
+                    bindExpressionStatement(<ExpressionStatement>node);
+                    break;
                 case SyntaxKind.LabeledStatement:
                     bindLabeledStatement(<LabeledStatement>node);
                     break;
@@ -896,6 +899,11 @@ namespace ts {
             return flowNodeCreated({ flags: FlowFlags.Assignment, antecedent, node });
         }
 
+        function createFlowCall(antecedent: FlowNode, node: CallExpression): FlowNode {
+            setFlowNodeReferenced(antecedent);
+            return flowNodeCreated({ flags: FlowFlags.Call, antecedent, node });
+        }
+
         function createFlowArrayMutation(antecedent: FlowNode, node: CallExpression | BinaryExpression): FlowNode {
             setFlowNodeReferenced(antecedent);
             const res: FlowArrayMutation = flowNodeCreated({ flags: FlowFlags.ArrayMutation, antecedent, node });
@@ -1276,6 +1284,20 @@ namespace ts {
             activeLabels!.pop();
         }
 
+        function isDottedName(node: Expression) {
+            return node.kind === SyntaxKind.Identifier || node.kind === SyntaxKind.PropertyAccessExpression && isQualifiedName((<PropertyAccessExpression>node).expression);
+        }
+
+        function bindExpressionStatement(node: ExpressionStatement): void {
+            bind(node.expression);
+            if (node.expression.kind === SyntaxKind.CallExpression) {
+                const call = <CallExpression>node.expression;
+                if (isDottedName(call.expression) && call.arguments.length >= 1) {
+                    currentFlow = createFlowCall(currentFlow, call);
+                }
+            }
+        }
+
         function bindLabeledStatement(node: LabeledStatement): void {
             const preStatementLabel = createLoopLabel();
             const postStatementLabel = createBranchLabel();

src/compiler/checker.ts

@@ -16864,6 +16864,44 @@ namespace ts {
             return false;
         }
 
+        function getTypeOfDottedName(node: Expression) {
+            if (node.kind === SyntaxKind.Identifier) {
+                const symbol = getResolvedSymbol(<Identifier>node);
+                const nonAliasSymbol = symbol.flags & SymbolFlags.Alias ? resolveAlias(symbol) : symbol;
+                return nonAliasSymbol.flags & (SymbolFlags.Function | SymbolFlags.Class | SymbolFlags.ValueModule) ? getTypeOfSymbol(nonAliasSymbol) : undefined;
+            }
+            if (node.kind === SyntaxKind.PropertyAccessExpression) {
+                const type = getTypeOfDottedName((<PropertyAccessExpression>node).expression);
+                if (type) {
+                    const prop = getPropertyOfType(type, (<PropertyAccessExpression>node).name.escapedText);
+                    return prop && prop.flags & (SymbolFlags.Function | SymbolFlags.Method | SymbolFlags.Class | SymbolFlags.ValueModule) ? getTypeOfSymbol(prop) : undefined;
+                }
+            }
+        }
+
+        function getIsAssertCall(node: CallExpression) {
+            const type = getTypeOfDottedName(node.expression);
+            if (type) {
+                const signature = getSingleCallSignature(type);
+                if (signature && signature.declaration) {
+                    const typeNode = getEffectiveReturnTypeNode(signature.declaration);
+                    if (typeNode && typeNode.kind === SyntaxKind.UnionType) {
+                        const types = (<UnionTypeNode>typeNode).types;
+                        return types.length === 2 && types[0].kind === SyntaxKind.VoidKeyword && types[1].kind === SyntaxKind.NeverKeyword;
+                    }
+                }
+            }
+            return false;
+        }
+
+        function isAssertCall(node: CallExpression) {
+            const links = getNodeLinks(node);
+            if (links.isAssertCall === undefined) {
+                links.isAssertCall = getIsAssertCall(node);
+            }
+            return links.isAssertCall;
+        }
+
         function reportFlowControlError(node: Node) {
             const block = <Block | ModuleBlock | SourceFile>findAncestor(node, isFunctionOrModuleBlock);
             const sourceFile = getSourceFileOfNode(node);
@@ -16962,6 +17000,13 @@ namespace ts {
                             }
                         }
                     }
+                    else if (flags & FlowFlags.Call) {
+                        type = getTypeAtFlowCall(<FlowCall>flow);
+                        if (!type) {
+                            flow = (<FlowCall>flow).antecedent;
+                            continue;
+                        }
+                    }
                     else if (flags & FlowFlags.Condition) {
                         type = getTypeAtFlowCondition(<FlowCondition>flow);
                     }
@@ -17057,6 +17102,32 @@ namespace ts {
                 return undefined;
             }
 
+            function narrowTypeByAssertion(type: Type, expr: Expression): Type {
+                const node = skipParentheses(expr);
+                if (node.kind === SyntaxKind.BinaryExpression) {
+                    if ((<BinaryExpression>node).operatorToken.kind === SyntaxKind.AmpersandAmpersandToken) {
+                        return narrowTypeByAssertion(narrowTypeByAssertion(type, (<BinaryExpression>node).left), (<BinaryExpression>node).right);
+                    }
+                    if ((<BinaryExpression>node).operatorToken.kind === SyntaxKind.BarBarToken) {
+                        return getUnionType([narrowTypeByAssertion(type, (<BinaryExpression>node).left), narrowTypeByAssertion(type, (<BinaryExpression>node).right)]);
+                    }
+                }
+                return narrowType(type, node, /*assumeTrue*/ true);
+            }
+
+            function getTypeAtFlowCall(flow: FlowCall): FlowType | undefined {
+                if (isAssertCall(flow.node)) {
+                    const flowType = getTypeAtFlowNode(flow.antecedent);
+                    const type = getTypeFromFlowType(flowType);
+                    const narrowedType = narrowTypeByAssertion(type, flow.node.arguments[0]);
+                    if (narrowedType === type) {
+                        return flowType;
+                    }
+                    return createFlowType(narrowedType, isIncomplete(flowType));
+                }
+                return undefined;
+            }
+
             function getTypeAtFlowArrayMutation(flow: FlowArrayMutation): FlowType | undefined {
                 if (declaredType === autoType || declaredType === autoArrayType) {
                     const node = flow.node;

src/compiler/types.ts

@@ -2550,12 +2550,13 @@ namespace ts {
         FalseCondition = 1 << 6,  // Condition known to be false
         SwitchClause   = 1 << 7,  // Switch statement clause
         ArrayMutation  = 1 << 8,  // Potential array mutation
-        Referenced     = 1 << 9,  // Referenced as antecedent once
-        Shared         = 1 << 10, // Referenced as antecedent more than once
-        PreFinally     = 1 << 11, // Injected edge that links pre-finally label and pre-try flow
-        AfterFinally   = 1 << 12, // Injected edge that links post-finally flow with the rest of the graph
+        Call           = 1 << 9,  // Potential assertion call
+        Referenced     = 1 << 10, // Referenced as antecedent once
+        Shared         = 1 << 11, // Referenced as antecedent more than once
+        PreFinally     = 1 << 12, // Injected edge that links pre-finally label and pre-try flow
+        AfterFinally   = 1 << 13, // Injected edge that links post-finally flow with the rest of the graph
         /** @internal */
-        Cached         = 1 << 13, // Indicates that at least one cross-call cache entry exists for this node, even if not a loop participant
+        Cached         = 1 << 14, // Indicates that at least one cross-call cache entry exists for this node, even if not a loop participant
         Label = BranchLabel | LoopLabel,
         Condition = TrueCondition | FalseCondition
     }
@@ -2574,7 +2575,7 @@ namespace ts {
     }
 
     export type FlowNode =
-        | AfterFinallyFlow | PreFinallyFlow | FlowStart | FlowLabel | FlowAssignment | FlowCondition | FlowSwitchClause | FlowArrayMutation;
+        | AfterFinallyFlow | PreFinallyFlow | FlowStart | FlowLabel | FlowAssignment | FlowCall | FlowCondition | FlowSwitchClause | FlowArrayMutation;
     export interface FlowNodeBase {
         flags: FlowFlags;
         id?: number;     // Node id used by flow type cache in checker
@@ -2599,6 +2600,11 @@ namespace ts {
         antecedent: FlowNode;
     }
 
+    export interface FlowCall extends FlowNodeBase {
+        node: CallExpression;
+        antecedent: FlowNode;
+    }
+
     // FlowCondition represents a condition that is known to be true or false at the
     // node's location in the control flow.
     export interface FlowCondition extends FlowNodeBase {
@@ -3902,6 +3908,7 @@ namespace ts {
         resolvedSymbol?: Symbol;          // Cached name resolution result
         resolvedIndexInfo?: IndexInfo;    // Cached indexing info resolution result
         maybeTypePredicate?: boolean;     // Cached check whether call expression might reference a type predicate
+        isAssertCall?: boolean;
         enumMemberValue?: string | number;  // Constant value of enum member
         isVisible?: boolean;              // Is this node visible
         containsArgumentsReference?: boolean; // Whether a function-like declaration contains an 'arguments' reference