Un-deprecate `length` and add guard #897

meeber · 2017-01-02T16:54:09Z

This PR is broken into two commits. The first commit makes length and lengthOf true aliases, with documentation updated to remove the deprecation notice and favor lengthOf over length. The second commit adds a guard against chaining length directly off of an uninvoked method assertion.

Closes .length(value) deprecation #684
Closes length as assertion => lengthOf #841

- The method part of the `length` assertion was slated for deprecation due to a compatibility issue in legacy environments. The decision to deprecate `length` was reversed per chaijs#684. This commit replaces the deprecation notice with a recommendation to favor `lengthOf` over `length` due to the compatibility issue. - The `lengthOf` assertion wasn't a true alias of `length` because it was a method assertion instead of a chainable method assertion. This commit changes `lengthOf` into a chainable method assertion that's identical to `length`, and updates tests and docs accordingly. - Updates docs to classify `length` as an alias of `lengthOf`. - Updates docs of related assertions to use `lengthOf` instead of `length`.

shvaikalesh · 2017-01-02T21:21:08Z

Great work, @meeber.

However, I think trapping length makes things more complicated than they could be. What about checking configurable attr of a function's length and set up a getter?

EDIT: why that's better:

proxiyfy: SRP (well, more specific responsibility), -1 parameter, easier logic
Works down to Node.js 4
Will make proxy optimizable

meeber · 2017-01-02T21:58:56Z

@shvaikalesh Seems like a good suggestion, even if only for the benefit of "Works down to Node.js 4". Can you elaborate on the third point about optimization?

lucasfcosta · 2017-01-02T22:37:07Z

Awesome work! Thanks @meeber!
As @shvaikalesh suggested, since we're targeting newer environments by fixing this problem with Proxies I think that checking for configurable length properties would be a great idea.

However, due to the fact that older browsers don't have neither configurable length nor Proxy support I think this is a problem we can't really handle without an explicit warning.

meeber · 2017-01-02T22:47:54Z

@lucasfcosta Just to make sure we're on the same page regarding your second point: With this PR, the proxy-based length protection would throw a helpful error message in environments that support proxies, but in other environments, it would still throw the somewhat vague error message that it currently does in master. Likewise, if I refactor this PR to instead use @shvaikalesh's suggestion, then the getter-based length protection would throw a helpful error message in environments that support configurable .length on functions, but in other environments, it would still throw the somewhat vague error message that it currently does in master. So either way, the error messages in the legacy environments aren't improved upon, but at least @shvaikalesh's idea allows more environments to benefit from the helpful error messages.

shvaikalesh · 2017-01-02T23:03:50Z

@meeber

Right now, we wrap every Assertion instance/chainable in proxy. That is kinda expensive. But what more expensive is that every [[Get]] getting trapped and invariant-checked.

Now

Correct method

Proxy {expensive} --> Assertion instance --> Assertion.prototype [hit!] -!- Object.prototype -!- null

Misspelled method

Proxy {expensive}[error!] -!- Assertion instance -!- Assertion.prototype [hit!] -!- Object.prototype -!- null

Suggested

Correct method

Assertion instance --> Assertion.prototype [hit!] -!- Proxy {expensive} -!- Object.prototype -!- null

Misspelled method

Assertion instance --> Assertion.prototype --> Proxy {expensive}[error!] -!- Object.prototype -!- null

EDIT: oops, sent too early.

So, by putting proxies upper on the prototype chain, [[Get]] will hit them only when they would throw and they won't reduce performance otherwise (tested in V8).

meeber · 2017-01-02T23:21:30Z

@shvaikalesh Gotcha. Seems like another strong reason to limit proxy protection to undefined properties.

meeber · 2017-01-03T01:21:22Z

Pushed a new version of this that uses getters instead of proxies.

shvaikalesh · 2017-01-03T01:26:43Z

lib/chai/utils/addLengthGuard.js

+var config = require('../config');
+
+var fnDesc = Object.getOwnPropertyDescriptor(function () {}, 'length');
+var isFnLengthConfigurable = typeof fnDesc === 'object'


Descriptor is guaranteed to be an object here.

shvaikalesh · 2017-01-03T01:27:22Z

lib/chai/utils/addLengthGuard.js

+ */
+
+module.exports = function addLengthGuard (fn, assertionName, isChainable) {
+  if (isFnLengthConfigurable !== true) return fn;


Maybe we can do if (!fnDesc.configurable) here?

shvaikalesh · 2017-01-03T01:28:17Z

lib/chai/utils/addLengthGuard.js

+
+  Object.defineProperty(fn, 'length', {
+    get: function () {
+      if (isChainable === true) {


Maybe if (isChainable) will suffice?

meeber · 2017-01-03T01:44:57Z

Updated!

shvaikalesh · 2017-01-03T01:56:46Z

test/utilities.js

+
+  describe('addLengthGuard', function () {
+    var fnDesc = Object.getOwnPropertyDescriptor(function () {}, 'length');
+    if (typeof fnDesc !== 'object' || fnDesc.configurable !== true) return;


I've missed this before. I believe, if (!fnDesc.configurable) would be enough.

When the `length` assertion is chained directly off of an uninvoked method, it references `function`'s built-in `length` property instead of Chai's `length` assertion. This commit adds a guard to Chai methods to detect this problem and throw a helpful error message that advises the user on how to correct it.

meeber · 2017-01-03T02:03:14Z

Gottem.

shvaikalesh · 2017-01-03T02:06:48Z

Thanks for addressing the issues, @meeber! LGTM.

PS. Maybe we should change PR title to reflect the changes?

keithamus · 2017-01-03T10:05:12Z

This LGTM too. I'll force a merge, LGTM.co is no longer working so we need to disable and find a workable alternative.

meeber force-pushed the proxy-length branch from 8fbe2c9 to ecfed03 Compare January 2, 2017 17:04

meeber force-pushed the proxy-length branch 3 times, most recently from 8cfcf1b to 3397835 Compare January 3, 2017 01:20

shvaikalesh reviewed Jan 3, 2017

View reviewed changes

meeber force-pushed the proxy-length branch from 3397835 to 048005a Compare January 3, 2017 01:42

shvaikalesh reviewed Jan 3, 2017

View reviewed changes

meeber force-pushed the proxy-length branch from 048005a to ce9a2c2 Compare January 3, 2017 02:01

meeber changed the title ~~Un-deprecate length and add proxy protection~~ Un-deprecate length and add guard Jan 3, 2017

keithamus merged commit c9bebe4 into chaijs:master Jan 3, 2017

shvaikalesh mentioned this pull request Jan 3, 2017

length as assertion => lengthOf chaijs/chaijs.github.io#143

Merged

meeber mentioned this pull request Jan 27, 2017

Rename .string to .substring (with alias .substr) #918

Closed

lucasfcosta mentioned this pull request May 10, 2017

4.x.x Complete Migration Guide #781

Closed

TimothyGu mentioned this pull request Jul 26, 2017

Detecting whether a method is chainable (and general concerns with breaking changes) #1010

Closed

meeber deleted the proxy-length branch August 6, 2017 13:49

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Un-deprecate length and add guard #897

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Now

Correct method

Misspelled method

Suggested

Correct method

Misspelled method

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Un-deprecate `length` and add guard #897

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