Adding more comments
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2 changed files with 15 additions and 2 deletions
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@ -8809,21 +8809,34 @@ namespace ts {
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const type = getTypeOfSymbol(localOrExportSymbol);
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const declaration = localOrExportSymbol.valueDeclaration;
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// We only narrow variables and parameters occurring in a non-assignment position. For all other
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// entities we simply return the declared type.
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if (!(localOrExportSymbol.flags & SymbolFlags.Variable) || isAssignmentTarget(node) || !declaration) {
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return type;
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}
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// The declaration container is the innermost function that encloses the declaration of the variable
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// or parameter. The flow container is the innermost function starting with which we analyze the control
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// flow graph to determine the control flow based type.
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const isParameter = getRootDeclaration(declaration).kind === SyntaxKind.Parameter;
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const declarationContainer = getControlFlowContainer(declaration);
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let flowContainer = getControlFlowContainer(node);
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// When the control flow originates in a function expression or arrow function and we are referencing
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// a const variable or parameter from an outer function, we extend the origin of the control flow
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// analysis to include the immediately enclosing function.
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while (flowContainer !== declarationContainer &&
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(flowContainer.kind === SyntaxKind.FunctionExpression || flowContainer.kind === SyntaxKind.ArrowFunction) &&
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(isReadonlySymbol(localOrExportSymbol) || isParameter && !isParameterAssigned(localOrExportSymbol))) {
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flowContainer = getControlFlowContainer(flowContainer);
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}
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// We only look for uninitialized variables in strict null checking mode, and only when we can analyze
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// the entire control flow graph from the variable's declaration (i.e. when the flow container and
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// declaration container are the same).
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const assumeInitialized = !strictNullChecks || (type.flags & TypeFlags.Any) !== 0 || isParameter ||
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flowContainer !== declarationContainer || isInAmbientContext(declaration);
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const flowType = getFlowTypeOfReference(node, type, assumeInitialized, flowContainer);
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// A variable is considered uninitialized when it is possible to analyze the entire control flow graph
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// from declaration to use, and when the variable's declared type doesn't include undefined but the
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// control flow based type does include undefined.
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if (!assumeInitialized && !(getFalsyFlags(type) & TypeFlags.Undefined) && getFalsyFlags(flowType) & TypeFlags.Undefined) {
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error(node, Diagnostics.Variable_0_is_used_before_being_assigned, symbolToString(symbol));
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// Return the declared type to reduce follow-on errors
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@ -2157,7 +2157,7 @@ namespace ts {
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/* @internal */ exportSymbol?: Symbol; // Exported symbol associated with this symbol
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/* @internal */ constEnumOnlyModule?: boolean; // True if module contains only const enums or other modules with only const enums
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/* @internal */ isReferenced?: boolean; // True if the symbol is referenced elsewhere
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/* @internal */ isAssigned?: boolean; // True if the symbol has assignments
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/* @internal */ isAssigned?: boolean; // True if the symbol is a parameter with assignments
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}
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/* @internal */
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