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This commit is contained in:
Anders Hejlsberg 2016-08-16 09:41:33 -07:00
parent 15dae3fd8a
commit 5770157504
2 changed files with 15 additions and 2 deletions
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15
src/compiler/checker.ts
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@ -8809,21 +8809,34 @@ namespace ts {
const type = getTypeOfSymbol(localOrExportSymbol);
const declaration = localOrExportSymbol.valueDeclaration;
// We only narrow variables and parameters occurring in a non-assignment position. For all other
// entities we simply return the declared type.
if (!(localOrExportSymbol.flags & SymbolFlags.Variable) || isAssignmentTarget(node) || !declaration) {
return type;
}
// The declaration container is the innermost function that encloses the declaration of the variable
// or parameter. The flow container is the innermost function starting with which we analyze the control
// flow graph to determine the control flow based type.
const isParameter = getRootDeclaration(declaration).kind === SyntaxKind.Parameter;
const declarationContainer = getControlFlowContainer(declaration);
let flowContainer = getControlFlowContainer(node);
// When the control flow originates in a function expression or arrow function and we are referencing
// a const variable or parameter from an outer function, we extend the origin of the control flow
// analysis to include the immediately enclosing function.
while (flowContainer !== declarationContainer &&
(flowContainer.kind === SyntaxKind.FunctionExpression || flowContainer.kind === SyntaxKind.ArrowFunction) &&
(isReadonlySymbol(localOrExportSymbol) || isParameter && !isParameterAssigned(localOrExportSymbol))) {
flowContainer = getControlFlowContainer(flowContainer);
}
// We only look for uninitialized variables in strict null checking mode, and only when we can analyze
// the entire control flow graph from the variable's declaration (i.e. when the flow container and
// declaration container are the same).
const assumeInitialized = !strictNullChecks || (type.flags & TypeFlags.Any) !== 0 || isParameter ||
flowContainer !== declarationContainer || isInAmbientContext(declaration);
const flowType = getFlowTypeOfReference(node, type, assumeInitialized, flowContainer);
// A variable is considered uninitialized when it is possible to analyze the entire control flow graph
// from declaration to use, and when the variable's declared type doesn't include undefined but the
// control flow based type does include undefined.
if (!assumeInitialized && !(getFalsyFlags(type) & TypeFlags.Undefined) && getFalsyFlags(flowType) & TypeFlags.Undefined) {
error(node, Diagnostics.Variable_0_is_used_before_being_assigned, symbolToString(symbol));
// Return the declared type to reduce follow-on errors

2
src/compiler/types.ts
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@ -2157,7 +2157,7 @@ namespace ts {
/* @internal */ exportSymbol?: Symbol; // Exported symbol associated with this symbol
/* @internal */ constEnumOnlyModule?: boolean; // True if module contains only const enums or other modules with only const enums
/* @internal */ isReferenced?: boolean; // True if the symbol is referenced elsewhere
/* @internal */ isAssigned?: boolean; // True if the symbol has assignments
/* @internal */ isAssigned?: boolean; // True if the symbol is a parameter with assignments
}
/* @internal */