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pelikhan merged 3 commits into from
Jul 23, 2026
+251 −65
Merged

Make no-unsafe-catch-error-property flow-sensitive to branch dominance and source order #47534

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7501382
Initial plan
Copilot Jul 23, 2026
a775e52
Fix guard flow sensitivity in no-unsafe-catch-error-property
Copilot Jul 23, 2026
b871203
Recognize early-exit instanceof guards (negated and else-return patte…
Copilot Jul 23, 2026
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100 changes: 100 additions & 0 deletions eslint-factory/src/rules/no-unsafe-catch-error-property.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -42,6 +42,58 @@ describe("no-unsafe-catch-error-property", () => {
});
});

it("valid: nested guard block that dominates access is allowed", () => {
cjsRuleTester.run("no-unsafe-catch-error-property", noUnsafeCatchErrorPropertyRule, {
valid: [`try { f(); } catch (err) { if (flag) { if (err instanceof Error) { console.log(err.stack); } } }`],
invalid: [],
});
});

it("valid: early-exit instanceof guard (negated) before access is recognized", () => {
cjsRuleTester.run("no-unsafe-catch-error-property", noUnsafeCatchErrorPropertyRule, {
valid: [
// if (!(err instanceof Error)) return; err.stack;
`try { f(); } catch (err) { if (!(err instanceof Error)) return; console.log(err.stack); }`,
// if (!(err instanceof Error)) { return; } err.stack;
`try { f(); } catch (err) { if (!(err instanceof Error)) { return; } console.log(err.stack); }`,
// if (!(err instanceof Error)) throw new TypeError(); err.stack;
`try { f(); } catch (err) { if (!(err instanceof Error)) throw new TypeError("not an error"); console.log(err.stack); }`,
// if (err instanceof Error) {} else return; err.stack;
`try { f(); } catch (err) { if (err instanceof Error) { doSomething(); } else return; console.log(err.stack); }`,
// if (err instanceof Error) {} else { return; } err.stack;
`try { f(); } catch (err) { if (err instanceof Error) { } else { return; } console.log(err.stack); }`,
// multiple safe properties after a single early-exit guard
`try { f(); } catch (err) { if (!(err instanceof Error)) return; console.log(err.message, err.stack); }`,
],
invalid: [],
});
});

it("invalid: early-exit guard without termination does not suppress access", () => {
cjsRuleTester.run("no-unsafe-catch-error-property", noUnsafeCatchErrorPropertyRule, {
valid: [],
invalid: [
{
// non-matching path does not terminate — access is still unsafe
code: `try { f(); } catch (err) { if (!(err instanceof Error)) console.log("not an error"); console.log(err.stack); }`,
errors: [
{
messageId: "unsafeProperty",
data: { prop: "stack", errorVar: "err" },
suggestions: [
{
messageId: "wrapWithInstanceof",
data: { errorVar: "err", prop: "stack" },
output: `try { f(); } catch (err) { if (!(err instanceof Error)) console.log("not an error"); console.log((err instanceof Error ? err.stack : undefined)); }`,
},
],
},
],
},
],
});
});

it("valid: property access on a different variable is not flagged", () => {
cjsRuleTester.run("no-unsafe-catch-error-property", noUnsafeCatchErrorPropertyRule, {
valid: [`try { f(); } catch (err) { console.log(otherObj.message); }`, `try { f(); } catch (err) { const e = new Error(); console.log(e.message); }`],
Expand Down Expand Up @@ -152,6 +204,54 @@ describe("no-unsafe-catch-error-property", () => {
});
});

it("invalid: sibling-branch guard does not suppress unguarded access", () => {
cjsRuleTester.run("no-unsafe-catch-error-property", noUnsafeCatchErrorPropertyRule, {
valid: [],
invalid: [
{
code: `try { f(); } catch (err) { if (flag) { core.info(err.message); } if (err instanceof Error) { core.info(err.stack); } }`,
errors: [
{
messageId: "unsafeProperty",
data: { prop: "message", errorVar: "err" },
suggestions: [
{
messageId: "useGetErrorMessage",
data: { errorVar: "err" },
output: `try { f(); } catch (err) { if (flag) { core.info(getErrorMessage(err)); } if (err instanceof Error) { core.info(err.stack); } }`,
},
],
},
],
},
],
});
});

it("invalid: guard after unsafe access does not suppress report", () => {
cjsRuleTester.run("no-unsafe-catch-error-property", noUnsafeCatchErrorPropertyRule, {
valid: [],
invalid: [
{
code: `try { f(); } catch (err) { console.log(err.stack); if (err instanceof Error) { core.info(err.message); } }`,
errors: [
{
messageId: "unsafeProperty",
data: { prop: "stack", errorVar: "err" },
suggestions: [
{
messageId: "wrapWithInstanceof",
data: { errorVar: "err", prop: "stack" },
output: `try { f(); } catch (err) { console.log((err instanceof Error ? err.stack : undefined)); if (err instanceof Error) { core.info(err.message); } }`,
},
],
},
],
},
],
});
});

it("invalid: err.stack without guard is flagged", () => {
cjsRuleTester.run("no-unsafe-catch-error-property", noUnsafeCatchErrorPropertyRule, {
valid: [],
Expand Down
216 changes: 151 additions & 65 deletions eslint-factory/src/rules/no-unsafe-catch-error-property.ts
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Original file line number Diff line number Diff line change
@@ -1,16 +1,25 @@
import { AST_NODE_TYPES, ESLintUtils, TSESTree } from "@typescript-eslint/utils";
import { AST_NODE_TYPES, ESLintUtils, TSESLint, TSESTree } from "@typescript-eslint/utils";

const createRule = ESLintUtils.RuleCreator(name => `https://github.com/github/gh-aw/tree/main/eslint-factory#${name}`);

const UNSAFE_PROPERTIES = new Set(["message", "stack", "code", "status", "cause", "name"]);

interface CatchFrame {
varName: string;
hasGuard: boolean;
hasNonNullGuard: boolean;
safeCalls: TSESTree.CallExpression[];
unsafeNodes: Array<{ node: TSESTree.MemberExpression; prop: string }>;
}

function isInstanceofExprCheck(node: TSESTree.Expression, varName: string): boolean {
return node.type === AST_NODE_TYPES.BinaryExpression && node.operator === "instanceof" && node.left.type === AST_NODE_TYPES.Identifier && node.left.name === varName;
}

function isTerminating(stmt: TSESTree.Statement): boolean {
if (stmt.type === AST_NODE_TYPES.ReturnStatement || stmt.type === AST_NODE_TYPES.ThrowStatement) return true;
if (stmt.type === AST_NODE_TYPES.BlockStatement) return stmt.body.length > 0 && isTerminating(stmt.body[stmt.body.length - 1]);
return false;
}

function isTypeofObjectCheck(node: TSESTree.Expression, varName: string): boolean {
if (node.type !== AST_NODE_TYPES.BinaryExpression || node.operator !== "===") return false;
const { left, right } = node;
Expand All @@ -35,6 +44,135 @@ function isNonNullGuardCheck(node: TSESTree.Expression, varName: string): boolea
return (isVarRef(node.left) && isNullLiteral(node.right)) || (isVarRef(node.right) && isNullLiteral(node.left));
}

function getNearestBlockEntry(sourceCode: Readonly<TSESLint.SourceCode>, node: TSESTree.Node): { block: TSESTree.BlockStatement; entry: TSESTree.Statement } | null {
const ancestors = sourceCode.getAncestors(node);
let current: TSESTree.Node = node;
for (let index = ancestors.length - 1; index >= 0; index--) {
const ancestor = ancestors[index];
if (ancestor.type === AST_NODE_TYPES.BlockStatement) {
const entry = ancestor.body.find(stmt => stmt === current);
if (entry) return { block: ancestor, entry };
}
current = ancestor;
}
return null;
}

function hasPriorNonNullReturnGuard(sourceCode: Readonly<TSESLint.SourceCode>, anchorNode: TSESTree.Node, varName: string): boolean {
const location = getNearestBlockEntry(sourceCode, anchorNode);
if (!location) return false;

const entryIndex = location.block.body.indexOf(location.entry);
for (let index = 0; index < entryIndex; index++) {
const stmt = location.block.body[index];
if (
stmt.type === AST_NODE_TYPES.IfStatement &&
stmt.test.type === AST_NODE_TYPES.UnaryExpression &&
stmt.test.operator === "!" &&
stmt.test.argument.type === AST_NODE_TYPES.Identifier &&
stmt.test.argument.name === varName &&
stmt.consequent.type === AST_NODE_TYPES.ReturnStatement
) {
return true;
}
}

return false;
}

// Recognizes early-exit instanceof narrowing patterns that precede the access in the same block:
// if (!(err instanceof Error)) return/throw; err.stack;
// if (err instanceof Error) { } else return/throw; err.stack;
function hasPriorEarlyExitInstanceofGuard(sourceCode: Readonly<TSESLint.SourceCode>, anchorNode: TSESTree.Node, varName: string): boolean {
const location = getNearestBlockEntry(sourceCode, anchorNode);
if (!location) return false;

const entryIndex = location.block.body.indexOf(location.entry);
for (let index = 0; index < entryIndex; index++) {
const stmt = location.block.body[index];
if (stmt.type !== AST_NODE_TYPES.IfStatement) continue;

const { test, consequent, alternate } = stmt;

// if (!(err instanceof Error)) return/throw
if (test.type === AST_NODE_TYPES.UnaryExpression && test.operator === "!" && isInstanceofExprCheck(test.argument, varName) && alternate === null && isTerminating(consequent)) {
return true;
}

// if (err instanceof Error) { ... } else return/throw
if (isInstanceofExprCheck(test, varName) && alternate !== null && isTerminating(alternate)) {
return true;
}
}

return false;
}

function isTruthyBranchGuarded(sourceCode: Readonly<TSESLint.SourceCode>, test: TSESTree.Expression, varName: string, guardNode: TSESTree.Node): boolean {
const conjuncts: TSESTree.Expression[] = [];
const collectConjuncts = (expr: TSESTree.Expression): void => {
if (expr.type === AST_NODE_TYPES.LogicalExpression && expr.operator === "&&") {
collectConjuncts(expr.left);
collectConjuncts(expr.right);
return;
}
conjuncts.push(expr);
};
collectConjuncts(test);

const hasInstanceof = conjuncts.some(expr => isInstanceofExprCheck(expr, varName));
if (hasInstanceof) return true;

const hasTypeofObject = conjuncts.some(expr => isTypeofObjectCheck(expr, varName));
const hasNonNullGuard = conjuncts.some(expr => isNonNullGuardCheck(expr, varName));

if (!hasTypeofObject) return false;
if (hasNonNullGuard) return true;
return hasPriorNonNullReturnGuard(sourceCode, guardNode, varName);
}

function isGuardedByAncestorBranch(sourceCode: Readonly<TSESLint.SourceCode>, node: TSESTree.MemberExpression, varName: string): boolean {
const ancestors = sourceCode.getAncestors(node);
let current: TSESTree.Node = node;
for (let index = ancestors.length - 1; index >= 0; index--) {
const ancestor = ancestors[index];

if (ancestor.type === AST_NODE_TYPES.IfStatement && ancestor.consequent === current) {
if (isTruthyBranchGuarded(sourceCode, ancestor.test, varName, ancestor)) return true;
Comment on lines +140 to +141
}

if (ancestor.type === AST_NODE_TYPES.ConditionalExpression && ancestor.consequent === current) {
if (isTruthyBranchGuarded(sourceCode, ancestor.test, varName, ancestor)) return true;
}

if (ancestor.type === AST_NODE_TYPES.LogicalExpression && ancestor.operator === "&&" && ancestor.right === current) {
if (isTruthyBranchGuarded(sourceCode, ancestor.left, varName, ancestor)) return true;
}

current = ancestor;
}

return false;
}

function isCallOrderingGuarded(sourceCode: Readonly<TSESLint.SourceCode>, node: TSESTree.MemberExpression, safeCalls: TSESTree.CallExpression[]): boolean {
const nodeLocation = getNearestBlockEntry(sourceCode, node);
if (!nodeLocation) return false;
const nodeEntryIndex = nodeLocation.block.body.indexOf(nodeLocation.entry);

for (const callNode of safeCalls) {
if (callNode.range[1] > node.range[0]) continue;
const callLocation = getNearestBlockEntry(sourceCode, callNode);
if (!callLocation || callLocation.block !== nodeLocation.block) continue;

const callEntryIndex = callLocation.block.body.indexOf(callLocation.entry);
if (callEntryIndex < nodeEntryIndex) return true;
if (callEntryIndex === nodeEntryIndex && callNode.range[1] <= node.range[0]) return true;
}

return false;
}

export const noUnsafeCatchErrorPropertyRule = createRule({
name: "no-unsafe-catch-error-property",
meta: {
Expand All @@ -52,6 +190,7 @@ export const noUnsafeCatchErrorPropertyRule = createRule({
},
defaultOptions: [],
create(context) {
const sourceCode = context.sourceCode;
const catchStack: CatchFrame[] = [];

return {
Expand All @@ -61,18 +200,22 @@ export const noUnsafeCatchErrorPropertyRule = createRule({
// Only handle simple identifier bindings; skip bare catch {} and destructuring patterns.
// Push a sentinel frame so CatchClause:exit always has a matching pop.
if (!param || param.type !== AST_NODE_TYPES.Identifier) {
catchStack.push({ varName: "", hasGuard: true, hasNonNullGuard: true, unsafeNodes: [] });
catchStack.push({ varName: "", safeCalls: [], unsafeNodes: [] });
return;
}

catchStack.push({ varName: param.name, hasGuard: false, hasNonNullGuard: false, unsafeNodes: [] });
catchStack.push({ varName: param.name, safeCalls: [], unsafeNodes: [] });
},

"CatchClause:exit"() {
const frame = catchStack.pop();
if (!frame || !frame.varName || frame.hasGuard) return;
if (!frame || !frame.varName) return;

for (const { node: memberExpr, prop } of frame.unsafeNodes) {
if (isGuardedByAncestorBranch(sourceCode, memberExpr, frame.varName) || isCallOrderingGuarded(sourceCode, memberExpr, frame.safeCalls) || hasPriorEarlyExitInstanceofGuard(sourceCode, memberExpr, frame.varName)) {
continue;
}

const { varName } = frame;
const parent = memberExpr.parent;
const isChained =
Expand Down Expand Up @@ -112,68 +255,11 @@ export const noUnsafeCatchErrorPropertyRule = createRule({
CallExpression(node) {
if (catchStack.length === 0) return;
const top = catchStack[catchStack.length - 1];
if (!top || top.hasGuard || !top.varName) return;
if (!top || !top.varName) return;

const firstArg = node.arguments[0];
if (node.callee.type === AST_NODE_TYPES.Identifier && node.callee.name === "getErrorMessage" && node.arguments.length >= 1 && firstArg.type === AST_NODE_TYPES.Identifier && firstArg.name === top.varName) {
top.hasGuard = true;
}
},

// Detect catchVar instanceof Error — also accepted as a safe guard
// Detect typeof catchVar === 'object' with a non-null companion guard
BinaryExpression(node) {
if (catchStack.length === 0) return;
const top = catchStack[catchStack.length - 1];
if (!top || top.hasGuard || !top.varName) return;

if (node.operator === "instanceof" && node.left.type === AST_NODE_TYPES.Identifier && node.left.name === top.varName) {
top.hasGuard = true;
return;
}

if (isTypeofObjectCheck(node, top.varName) && top.hasNonNullGuard) {
top.hasGuard = true;
}
},

LogicalExpression(node) {
if (catchStack.length === 0) return;
const top = catchStack[catchStack.length - 1];
if (!top || top.hasGuard || !top.varName || node.operator !== "&&") return;

const conjuncts: TSESTree.Expression[] = [];
const collectConjuncts = (expr: TSESTree.Expression): void => {
if (expr.type === AST_NODE_TYPES.LogicalExpression && expr.operator === "&&") {
collectConjuncts(expr.left);
collectConjuncts(expr.right);
return;
}
conjuncts.push(expr);
};
collectConjuncts(node);

const hasTypeofObject = conjuncts.some(expr => isTypeofObjectCheck(expr, top.varName));
const hasNonNullGuard = conjuncts.some(expr => isNonNullGuardCheck(expr, top.varName));
if (hasTypeofObject && hasNonNullGuard) {
top.hasGuard = true;
top.hasNonNullGuard = true;
}
},

IfStatement(node) {
if (catchStack.length === 0) return;
const top = catchStack[catchStack.length - 1];
if (!top || top.hasGuard || !top.varName) return;

if (
node.test.type === AST_NODE_TYPES.UnaryExpression &&
node.test.operator === "!" &&
node.test.argument.type === AST_NODE_TYPES.Identifier &&
node.test.argument.name === top.varName &&
node.consequent.type === AST_NODE_TYPES.ReturnStatement
) {
top.hasNonNullGuard = true;
top.safeCalls.push(node);
}
},

Expand Down