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util: only inspect error properties that are not visible otherwise
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Inspecting errors results in duplicated information in case an error
is created with enumerable `name`, `message` or `stack` properties.
In that case, check if the output already contains that information
and prevent listing that property.

This reduces the noise as receiver.

PR-URL: nodejs#32327
Reviewed-By: Anto Aravinth <anto.aravinth.cse@gmail.com>
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BridgeAR authored and addaleax committed Apr 2, 2020
1 parent e20b4f9 commit 6baddcf
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Showing 2 changed files with 36 additions and 2 deletions.
16 changes: 14 additions & 2 deletions lib/internal/util/inspect.js
Expand Up @@ -890,7 +890,7 @@ function formatRaw(ctx, value, recurseTimes, typedArray) {
return ctx.stylize(base, 'date');
}
} else if (isError(value)) {
base = formatError(value, constructor, tag, ctx);
base = formatError(value, constructor, tag, ctx, keys);
if (keys.length === 0 && protoProps === undefined)
return base;
} else if (isAnyArrayBuffer(value)) {
Expand Down Expand Up @@ -1083,11 +1083,23 @@ function getFunctionBase(value, constructor, tag) {
return base;
}

function formatError(err, constructor, tag, ctx) {
function formatError(err, constructor, tag, ctx, keys) {
const name = err.name != null ? String(err.name) : 'Error';
let len = name.length;
let stack = err.stack ? String(err.stack) : ErrorPrototypeToString(err);

// Do not "duplicate" error properties that are already included in the output
// otherwise.
if (!ctx.showHidden && keys.length !== 0) {
for (const name of ['name', 'message', 'stack']) {
const index = keys.indexOf(name);
// Only hide the property in case it's part of the original stack
if (index !== -1 && stack.includes(err[name])) {
keys.splice(index, 1);
}
}
}

// A stack trace may contain arbitrary data. Only manipulate the output
// for "regular errors" (errors that "look normal") for now.
if (constructor === null ||
Expand Down
22 changes: 22 additions & 0 deletions test/parallel/test-util-inspect.js
Expand Up @@ -697,6 +697,28 @@ assert.strictEqual(util.inspect(-5e-324), '-5e-324');
Error.stackTraceLimit = tmp;
}

// Prevent enumerable error properties from being printed.
{
let err = new Error();
err.message = 'foobar';
let out = util.inspect(err).split('\n');
assert.strictEqual(out[0], 'Error: foobar');
assert(out[out.length - 1].startsWith(' at '));
// Reset the error, the stack is otherwise not recreated.
err = new Error();
err.message = 'foobar';
err.name = 'Unique';
Object.defineProperty(err, 'stack', { value: err.stack, enumerable: true });
out = util.inspect(err).split('\n');
assert.strictEqual(out[0], 'Unique: foobar');
assert(out[out.length - 1].startsWith(' at '));
err.name = 'Baz';
out = util.inspect(err).split('\n');
assert.strictEqual(out[0], 'Unique: foobar');
assert.strictEqual(out[out.length - 2], " name: 'Baz'");
assert.strictEqual(out[out.length - 1], '}');
}

// Doesn't capture stack trace.
{
function BadCustomError(msg) {
Expand Down

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