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🤖 Pick PR #62751 (Move unreachable checks to checker) into tsgo-port #62760

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Merged
merged 2 commits into from
Nov 14, 2025
+1,270 −156
Merged

🤖 Pick PR #62751 (Move unreachable checks to checker) into tsgo-port #62760

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45f30b3
Move unreachable checks to checker (#62751)
jakebailey Nov 14, 2025
ec0f9c5
Update baselines
typescript-bot Nov 14, 2025
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139 changes: 13 additions & 126 deletions src/compiler/binder.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -46,7 +46,6 @@ import {
DeleteExpression,
DestructuringAssignment,
DiagnosticArguments,
DiagnosticCategory,
DiagnosticMessage,
DiagnosticRelatedInformation,
Diagnostics,
Expand Down Expand Up @@ -87,7 +86,6 @@ import {
getAssignmentDeclarationKind,
getAssignmentDeclarationPropertyAccessKind,
getCombinedModifierFlags,
getCombinedNodeFlags,
getContainingClass,
getEffectiveContainerForJSDocTemplateTag,
getElementOrPropertyAccessName,
Expand All @@ -105,7 +103,6 @@ import {
getNameOfDeclaration,
getNameOrArgument,
getNodeId,
getRangesWhere,
getRightMostAssignedExpression,
getSourceFileOfNode,
getSourceTextOfNodeFromSourceFile,
Expand All @@ -114,10 +111,8 @@ import {
getSymbolNameForPrivateIdentifier,
getTextOfIdentifierOrLiteral,
getThisContainer,
getTokenPosOfNode,
HasContainerFlags,
hasDynamicName,
HasFlowNode,
hasJSDocNodes,
HasLocals,
hasSyntacticModifier,
Expand Down Expand Up @@ -163,7 +158,6 @@ import {
isExternalModule,
isExternalOrCommonJsModule,
isForInOrOfStatement,
isFunctionDeclaration,
isFunctionLike,
isFunctionLikeDeclaration,
isFunctionLikeOrClassStaticBlockDeclaration,
Expand Down Expand Up @@ -203,6 +197,7 @@ import {
isParenthesizedExpression,
isPartOfParameterDeclaration,
isPartOfTypeQuery,
isPotentiallyExecutableNode,
isPrefixUnaryExpression,
isPrivateIdentifier,
isPrologueDirective,
Expand All @@ -216,8 +211,6 @@ import {
isSignedNumericLiteral,
isSourceFile,
isSpecialPropertyDeclaration,
isStatement,
isStatementButNotDeclaration,
isStatic,
isString,
isStringLiteralLike,
Expand Down Expand Up @@ -284,10 +277,8 @@ import {
setParentRecursive,
setValueDeclaration,
ShorthandPropertyAssignment,
shouldPreserveConstEnums,
SignatureDeclaration,
skipParentheses,
sliceAfter,
some,
SourceFile,
SpreadElement,
Expand All @@ -300,7 +291,6 @@ import {
symbolName,
SymbolTable,
SyntaxKind,
TextRange,
ThisExpression,
ThrowStatement,
tokenToString,
Expand All @@ -313,8 +303,6 @@ import {
TypeOfExpression,
TypeParameterDeclaration,
unescapeLeadingUnderscores,
unreachableCodeIsError,
unusedLabelIsError,
VariableDeclaration,
WhileStatement,
WithStatement,
Expand Down Expand Up @@ -562,7 +550,6 @@ function createBinder(): (file: SourceFile, options: CompilerOptions) => void {
var classifiableNames: Set<__String>;

var unreachableFlow = createFlowNode(FlowFlags.Unreachable, /*node*/ undefined, /*antecedent*/ undefined);
var reportedUnreachableFlow = createFlowNode(FlowFlags.Unreachable, /*node*/ undefined, /*antecedent*/ undefined);
var bindBinaryExpressionFlow = createBindBinaryExpressionFlow();
/* eslint-enable no-var */

Expand All @@ -588,7 +575,6 @@ function createBinder(): (file: SourceFile, options: CompilerOptions) => void {

// Attach debugging information if necessary
Debug.attachFlowNodeDebugInfo(unreachableFlow);
Debug.attachFlowNodeDebugInfo(reportedUnreachableFlow);

if (!file.locals) {
tracing?.push(tracing.Phase.Bind, "bindSourceFile", { path: file.path }, /*separateBeginAndEnd*/ true);
Expand Down Expand Up @@ -1099,18 +1085,24 @@ function createBinder(): (file: SourceFile, options: CompilerOptions) => void {
// Most nodes aren't valid in an assignment pattern, so we clear the value here
// and set it before we descend into nodes that could actually be part of an assignment pattern.
inAssignmentPattern = false;
if (checkUnreachable(node)) {
if (canHaveFlowNode(node) && node.flowNode) {

if (currentFlow === unreachableFlow) {
if (canHaveFlowNode(node)) {
node.flowNode = undefined;
}
if (isPotentiallyExecutableNode(node)) {
(node as Mutable<Node>).flags |= NodeFlags.Unreachable;
}
bindEachChild(node);
bindJSDoc(node);
inAssignmentPattern = saveInAssignmentPattern;
return;
}
if (node.kind >= SyntaxKind.FirstStatement && node.kind <= SyntaxKind.LastStatement && (!options.allowUnreachableCode || node.kind === SyntaxKind.ReturnStatement)) {
(node as HasFlowNode).flowNode = currentFlow;

if (SyntaxKind.FirstStatement <= node.kind && node.kind <= SyntaxKind.LastStatement && canHaveFlowNode(node)) {
node.flowNode = currentFlow;
}

switch (node.kind) {
case SyntaxKind.WhileStatement:
bindWhileStatement(node as WhileStatement);
Expand Down Expand Up @@ -1788,8 +1780,8 @@ function createBinder(): (file: SourceFile, options: CompilerOptions) => void {
};
bind(node.label);
bind(node.statement);
if (!activeLabelList.referenced && !options.allowUnusedLabels) {
errorOrSuggestionOnNode(unusedLabelIsError(options), node.label, Diagnostics.Unused_label);
if (!activeLabelList.referenced) {
(node.label as Mutable<Node>).flags |= NodeFlags.Unreachable;
}
activeLabelList = activeLabelList.next;
addAntecedent(postStatementLabel, currentFlow);
Expand Down Expand Up @@ -2708,24 +2700,6 @@ function createBinder(): (file: SourceFile, options: CompilerOptions) => void {
file.bindDiagnostics.push(createFileDiagnostic(file, span.start, span.length, message, ...args));
}

function errorOrSuggestionOnNode(isError: boolean, node: Node, message: DiagnosticMessage): void {
errorOrSuggestionOnRange(isError, node, node, message);
}

function errorOrSuggestionOnRange(isError: boolean, startNode: Node, endNode: Node, message: DiagnosticMessage): void {
addErrorOrSuggestionDiagnostic(isError, { pos: getTokenPosOfNode(startNode, file), end: endNode.end }, message);
}

function addErrorOrSuggestionDiagnostic(isError: boolean, range: TextRange, message: DiagnosticMessage): void {
const diag = createFileDiagnostic(file, range.pos, range.end - range.pos, message);
if (isError) {
file.bindDiagnostics.push(diag);
}
else {
file.bindSuggestionDiagnostics = append(file.bindSuggestionDiagnostics, { ...diag, category: DiagnosticCategory.Suggestion });
}
}

function bind(node: Node | undefined): void {
if (!node) {
return;
Expand Down Expand Up @@ -3757,93 +3731,6 @@ function createBinder(): (file: SourceFile, options: CompilerOptions) => void {
declareSymbolAndAddToSymbolTable(node, SymbolFlags.TypeParameter, SymbolFlags.TypeParameterExcludes);
}
}

// reachability checks

function shouldReportErrorOnModuleDeclaration(node: ModuleDeclaration): boolean {
const instanceState = getModuleInstanceState(node);
return instanceState === ModuleInstanceState.Instantiated || (instanceState === ModuleInstanceState.ConstEnumOnly && shouldPreserveConstEnums(options));
}

function checkUnreachable(node: Node): boolean {
if (!(currentFlow.flags & FlowFlags.Unreachable)) {
return false;
}
if (currentFlow === unreachableFlow) {
const reportError =
// report error on all statements except empty ones
(isStatementButNotDeclaration(node) && node.kind !== SyntaxKind.EmptyStatement) ||
// report error on class declarations
node.kind === SyntaxKind.ClassDeclaration ||
// report errors on enums with preserved emit
isEnumDeclarationWithPreservedEmit(node, options) ||
// report error on instantiated modules
(node.kind === SyntaxKind.ModuleDeclaration && shouldReportErrorOnModuleDeclaration(node as ModuleDeclaration));

if (reportError) {
currentFlow = reportedUnreachableFlow;

if (!options.allowUnreachableCode) {
// unreachable code is reported if
// - user has explicitly asked about it AND
// - statement is in not ambient context (statements in ambient context is already an error
// so we should not report extras) AND
// - node is not variable statement OR
// - node is block scoped variable statement OR
// - node is not block scoped variable statement and at least one variable declaration has initializer
// Rationale: we don't want to report errors on non-initialized var's since they are hoisted
// On the other side we do want to report errors on non-initialized 'lets' because of TDZ
const isError = unreachableCodeIsError(options) &&
!(node.flags & NodeFlags.Ambient) &&
(
!isVariableStatement(node) ||
!!(getCombinedNodeFlags(node.declarationList) & NodeFlags.BlockScoped) ||
node.declarationList.declarations.some(d => !!d.initializer)
);

eachUnreachableRange(node, options, (start, end) => errorOrSuggestionOnRange(isError, start, end, Diagnostics.Unreachable_code_detected));
}
}
}
return true;
}
}

function isEnumDeclarationWithPreservedEmit(node: Node, options: CompilerOptions): boolean {
return node.kind === SyntaxKind.EnumDeclaration && (!isEnumConst(node as EnumDeclaration) || shouldPreserveConstEnums(options));
}

function eachUnreachableRange(node: Node, options: CompilerOptions, cb: (start: Node, last: Node) => void): void {
if (isStatement(node) && isExecutableStatement(node) && isBlock(node.parent)) {
const { statements } = node.parent;
const slice = sliceAfter(statements, node);
getRangesWhere(slice, isExecutableStatement, (start, afterEnd) => cb(slice[start], slice[afterEnd - 1]));
}
else {
cb(node, node);
}

// As opposed to a pure declaration like an `interface`
function isExecutableStatement(s: Statement): boolean {
// Don't remove statements that can validly be used before they appear.
return !isFunctionDeclaration(s) && !isPurelyTypeDeclaration(s) &&
// `var x;` may declare a variable used above
!(isVariableStatement(s) && !(getCombinedNodeFlags(s) & (NodeFlags.BlockScoped)) && s.declarationList.declarations.some(d => !d.initializer));
}

function isPurelyTypeDeclaration(s: Statement): boolean {
switch (s.kind) {
case SyntaxKind.InterfaceDeclaration:
case SyntaxKind.TypeAliasDeclaration:
return true;
case SyntaxKind.ModuleDeclaration:
return getModuleInstanceState(s as ModuleDeclaration) !== ModuleInstanceState.Instantiated;
case SyntaxKind.EnumDeclaration:
return !isEnumDeclarationWithPreservedEmit(s, options);
default:
return false;
}
}
}

/** @internal */
Expand Down
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