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Discriminated union types #9163

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merged 6 commits into from
Jun 17, 2016
Merged

Discriminated union types #9163

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4a8f94a
Type guards using discriminant properties of string literal types
ahejlsberg Jun 10, 2016
ce15646
Narrow type in case/default sections in switch on discriminant property
ahejlsberg Jun 13, 2016
c90b0fe
No implicit returns following exhaustive switch statements
ahejlsberg Jun 13, 2016
00376f4
Narrow non-union types to ensure consistent results
ahejlsberg Jun 14, 2016
5ff7c29
Add tests
ahejlsberg Jun 14, 2016
a3635cc
Merge branch 'master' into typeGuardDiscriminants
ahejlsberg Jun 14, 2016
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138 changes: 90 additions & 48 deletions src/compiler/binder.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -578,20 +578,14 @@ namespace ts {
}
}

function isNarrowableReference(expr: Expression): boolean {
return expr.kind === SyntaxKind.Identifier ||
expr.kind === SyntaxKind.ThisKeyword ||
expr.kind === SyntaxKind.PropertyAccessExpression && isNarrowableReference((<PropertyAccessExpression>expr).expression);
}

function isNarrowingExpression(expr: Expression): boolean {
switch (expr.kind) {
case SyntaxKind.Identifier:
case SyntaxKind.ThisKeyword:
case SyntaxKind.PropertyAccessExpression:
return isNarrowableReference(expr);
case SyntaxKind.CallExpression:
return true;
return hasNarrowableArgument(<CallExpression>expr);
case SyntaxKind.ParenthesizedExpression:
return isNarrowingExpression((<ParenthesizedExpression>expr).expression);
case SyntaxKind.BinaryExpression:
Expand All @@ -602,6 +596,39 @@ namespace ts {
return false;
}

function isNarrowableReference(expr: Expression): boolean {
return expr.kind === SyntaxKind.Identifier ||
expr.kind === SyntaxKind.ThisKeyword ||
expr.kind === SyntaxKind.PropertyAccessExpression && isNarrowableReference((<PropertyAccessExpression>expr).expression);
}

function hasNarrowableArgument(expr: CallExpression) {
if (expr.arguments) {
for (const argument of expr.arguments) {
if (isNarrowableReference(argument)) {
return true;
}
}
}
if (expr.expression.kind === SyntaxKind.PropertyAccessExpression &&
isNarrowableReference((<PropertyAccessExpression>expr.expression).expression)) {
return true;
}
return false;
}

function isNarrowingNullCheckOperands(expr1: Expression, expr2: Expression) {
return (expr1.kind === SyntaxKind.NullKeyword || expr1.kind === SyntaxKind.Identifier && (<Identifier>expr1).text === "undefined") && isNarrowableOperand(expr2);
}

function isNarrowingTypeofOperands(expr1: Expression, expr2: Expression) {
return expr1.kind === SyntaxKind.TypeOfExpression && isNarrowableOperand((<TypeOfExpression>expr1).expression) && expr2.kind === SyntaxKind.StringLiteral;
}

function isNarrowingDiscriminant(expr: Expression) {
return expr.kind === SyntaxKind.PropertyAccessExpression && isNarrowableReference((<PropertyAccessExpression>expr).expression);
}

function isNarrowingBinaryExpression(expr: BinaryExpression) {
switch (expr.operatorToken.kind) {
case SyntaxKind.EqualsToken:
Expand All @@ -610,34 +637,35 @@ namespace ts {
case SyntaxKind.ExclamationEqualsToken:
case SyntaxKind.EqualsEqualsEqualsToken:
case SyntaxKind.ExclamationEqualsEqualsToken:
if ((isNarrowingExpression(expr.left) && (expr.right.kind === SyntaxKind.NullKeyword || expr.right.kind === SyntaxKind.Identifier)) ||
(isNarrowingExpression(expr.right) && (expr.left.kind === SyntaxKind.NullKeyword || expr.left.kind === SyntaxKind.Identifier))) {
return true;
}
if (isTypeOfNarrowingBinaryExpression(expr)) {
return true;
}
return false;
return isNarrowingNullCheckOperands(expr.right, expr.left) || isNarrowingNullCheckOperands(expr.left, expr.right) ||
isNarrowingTypeofOperands(expr.right, expr.left) || isNarrowingTypeofOperands(expr.left, expr.right) ||
isNarrowingDiscriminant(expr.left) || isNarrowingDiscriminant(expr.right);
case SyntaxKind.InstanceOfKeyword:
return isNarrowingExpression(expr.left);
return isNarrowableOperand(expr.left);
case SyntaxKind.CommaToken:
return isNarrowingExpression(expr.right);
}
return false;
}

function isTypeOfNarrowingBinaryExpression(expr: BinaryExpression) {
let typeOf: Expression;
if (expr.left.kind === SyntaxKind.StringLiteral) {
typeOf = expr.right;
}
else if (expr.right.kind === SyntaxKind.StringLiteral) {
typeOf = expr.left;
}
else {
typeOf = undefined;
function isNarrowableOperand(expr: Expression): boolean {
switch (expr.kind) {
case SyntaxKind.ParenthesizedExpression:
return isNarrowableOperand((<ParenthesizedExpression>expr).expression);
case SyntaxKind.BinaryExpression:
switch ((<BinaryExpression>expr).operatorToken.kind) {
case SyntaxKind.EqualsToken:
return isNarrowableOperand((<BinaryExpression>expr).left);
case SyntaxKind.CommaToken:
return isNarrowableOperand((<BinaryExpression>expr).right);
}
}
return typeOf && typeOf.kind === SyntaxKind.TypeOfExpression && isNarrowingExpression((<TypeOfExpression>typeOf).expression);
return isNarrowableReference(expr);
}

function isNarrowingSwitchStatement(switchStatement: SwitchStatement) {
const expr = switchStatement.expression;
return expr.kind === SyntaxKind.PropertyAccessExpression && isNarrowableReference((<PropertyAccessExpression>expr).expression);
}

function createBranchLabel(): FlowLabel {
Expand Down Expand Up @@ -683,8 +711,22 @@ namespace ts {
setFlowNodeReferenced(antecedent);
return <FlowCondition>{
flags,
antecedent,
expression,
antecedent
};
}

function createFlowSwitchClause(antecedent: FlowNode, switchStatement: SwitchStatement, clauseStart: number, clauseEnd: number): FlowNode {
if (!isNarrowingSwitchStatement(switchStatement)) {
return antecedent;
}
setFlowNodeReferenced(antecedent);
return <FlowSwitchClause>{
flags: FlowFlags.SwitchClause,
switchStatement,
clauseStart,
clauseEnd,
antecedent
};
}

Expand Down Expand Up @@ -913,9 +955,12 @@ namespace ts {
preSwitchCaseFlow = currentFlow;
bind(node.caseBlock);
addAntecedent(postSwitchLabel, currentFlow);
const hasNonEmptyDefault = forEach(node.caseBlock.clauses, c => c.kind === SyntaxKind.DefaultClause && c.statements.length);
if (!hasNonEmptyDefault) {
addAntecedent(postSwitchLabel, preSwitchCaseFlow);
const hasDefault = forEach(node.caseBlock.clauses, c => c.kind === SyntaxKind.DefaultClause);
// We mark a switch statement as possibly exhaustive if it has no default clause and if all
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Why is a switch/case non-exhaustive if it has a default? I feel like if it does, it is definitely exhaustive (because it accounts for all cases the user hasn't explicitly accounted for). Can you also document the answer in a comment here?

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If it has a default clause it is definitely exhaustive and not just possibly exhaustive. We already handle the definitely exhaustive case through normal control flow analysis (i.e. if all branches exit the post-switch label will have no antecedents).

// case clauses have unreachable end points (e.g. they all return).
node.possiblyExhaustive = !hasDefault && !postSwitchLabel.antecedents;
if (!hasDefault) {
addAntecedent(postSwitchLabel, createFlowSwitchClause(preSwitchCaseFlow, node, 0, 0));
}
currentBreakTarget = saveBreakTarget;
preSwitchCaseFlow = savePreSwitchCaseFlow;
Expand All @@ -924,25 +969,22 @@ namespace ts {

function bindCaseBlock(node: CaseBlock): void {
const clauses = node.clauses;
let fallthroughFlow = unreachableFlow;
for (let i = 0; i < clauses.length; i++) {
const clause = clauses[i];
if (clause.statements.length) {
if (currentFlow.flags & FlowFlags.Unreachable) {
currentFlow = preSwitchCaseFlow;
}
else {
const preCaseLabel = createBranchLabel();
addAntecedent(preCaseLabel, preSwitchCaseFlow);
addAntecedent(preCaseLabel, currentFlow);
currentFlow = finishFlowLabel(preCaseLabel);
}
bind(clause);
if (!(currentFlow.flags & FlowFlags.Unreachable) && i !== clauses.length - 1 && options.noFallthroughCasesInSwitch) {
errorOnFirstToken(clause, Diagnostics.Fallthrough_case_in_switch);
}
const clauseStart = i;
while (!clauses[i].statements.length && i + 1 < clauses.length) {
bind(clauses[i]);
i++;
}
else {
bind(clause);
const preCaseLabel = createBranchLabel();
addAntecedent(preCaseLabel, createFlowSwitchClause(preSwitchCaseFlow, <SwitchStatement>node.parent, clauseStart, i + 1));
addAntecedent(preCaseLabel, fallthroughFlow);
currentFlow = finishFlowLabel(preCaseLabel);
const clause = clauses[i];
bind(clause);
fallthroughFlow = currentFlow;
if (!(currentFlow.flags & FlowFlags.Unreachable) && i !== clauses.length - 1 && options.noFallthroughCasesInSwitch) {
errorOnFirstToken(clause, Diagnostics.Fallthrough_case_in_switch);
}
}
}
Expand Down
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