More reliable mechanism for `_this`/`_super` simplification #56130

rbuckton · 2023-10-16T19:54:43Z

This changes the somewhat fragile way we handled the simplification of constructor body statements when transforming super() that became even more fragile in TS 5.2. These simplifications were intended to slim down transformed constructor bodies when a temporary variable like _this may not be necessary:

// given
class C extends Base {
  constructor() {
    super();
  }
}

// without simplification
var C = (function (_super) {
    function C() {
        var _this = this;
        _this = _super.call(this) || this;
        return _this;
    }
    return C;
})(Base);

// with simplificaiton
var C = (function (_super) {
    function C() {
        return _super.call(this) || this;
    }
    return C;
})(Base);

However, when using was introduced in TS 5.2, the simplification mechanism became more complicated as the super() statements we would normally look for would be moved inside of a try..catch..finally block if the constructor contained a using declaration.

Rather than try to handle specific super() simplifications when initially visiting the constructor body, this PR instead performs these simplifications in a second pass after the initial transformation completes. This results in a mechanism that is more reliable than the prior approach as it only performs these simplifications with complete knowledge of the transformed result..

Fixes #55646
Fixes #55637

rbuckton · 2023-10-16T19:55:38Z

@typescript-bot perf test

typescript-bot · 2023-10-16T19:55:41Z

Heya @rbuckton, I've started to run the regular perf test suite on this PR at 21a697d. You can monitor the build here.

Update: The results are in!

typescript-bot · 2023-10-16T20:17:47Z

@rbuckton
The results of the perf run you requested are in!

Here they are:

Compiler

Comparison Report - baseline..pr

_Metric	_baseline	_pr	_Delta	_Best	_Worst	_p-value
_{Angular - node (v18.15.0, x64)}
_{Memory used}	_{295,079k (± 0.02%)}	_{295,145k (± 0.01%)}	_{+66k (+ 0.02%)}	_295,098k	_295,207k	_{p=0.020 n=6}
_{Parse Time}	_{2.62s (± 0.92%)}	_{2.64s (± 0.52%)}	_~	_2.61s	_2.65s	_{p=0.506 n=6}
_{Bind Time}	_{0.84s (± 1.17%)}	_{0.84s (± 1.06%)}	_~	_0.83s	_0.85s	_{p=0.798 n=6}
_{Check Time}	_{8.07s (± 0.31%)}	_{8.08s (± 0.22%)}	_~	_8.05s	_8.10s	_{p=0.463 n=6}
_{Emit Time}	_{7.05s (± 0.19%)}	_{7.09s (± 0.28%)}	_{+0.04s (+ 0.61%)}	_7.06s	_7.12s	_{p=0.008 n=6}
_{Total Time}	_{18.58s (± 0.19%)}	_{18.65s (± 0.22%)}	_{+0.07s (+ 0.36%)}	_18.60s	_18.72s	_{p=0.010 n=6}
_{Compiler-Unions - node (v18.15.0, x64)}
_{Memory used}	_{193,542k (± 1.65%)}	_{191,631k (± 1.24%)}	_~	_190,642k	_196,499k	_{p=1.000 n=6}
_{Parse Time}	_{1.34s (± 0.82%)}	_{1.35s (± 1.46%)}	_~	_1.32s	_1.38s	_{p=0.611 n=6}
_{Bind Time}	_{0.73s (± 0.00%)}	_{0.73s (± 0.00%)}	_~	_0.73s	_0.73s	_{p=1.000 n=6}
_{Check Time}	_{9.13s (± 0.27%)}	_{9.12s (± 0.30%)}	_~	_9.09s	_9.16s	_{p=0.629 n=6}
_{Emit Time}	_{2.64s (± 0.37%)}	_{2.63s (± 0.44%)}	_~	_2.61s	_2.64s	_{p=0.209 n=6}
_{Total Time}	_{13.84s (± 0.26%)}	_{13.83s (± 0.17%)}	_~	_13.80s	_13.86s	_{p=0.464 n=6}
_{Monaco - node (v18.15.0, x64)}
_{Memory used}	_{347,292k (± 0.00%)}	_{347,355k (± 0.01%)}	_{+63k (+ 0.02%)}	_347,313k	_347,421k	_{p=0.005 n=6}
_{Parse Time}	_{2.45s (± 0.31%)}	_{2.45s (± 0.17%)}	_~	_2.45s	_2.46s	_{p=1.000 n=6}
_{Bind Time}	_{0.94s (± 0.87%)}	_{0.94s (± 0.55%)}	_~	_0.94s	_0.95s	_{p=0.114 n=6}
_{Check Time}	_{6.90s (± 0.49%)}	_{6.91s (± 0.44%)}	_~	_6.87s	_6.95s	_{p=0.376 n=6}
_{Emit Time}	_{4.03s (± 0.51%)}	_{4.04s (± 0.40%)}	_~	_4.02s	_4.07s	_{p=0.255 n=6}
_{Total Time}	_{14.32s (± 0.34%)}	_{14.35s (± 0.19%)}	_~	_14.31s	_14.38s	_{p=0.260 n=6}
_{TFS - node (v18.15.0, x64)}
_{Memory used}	_{302,543k (± 0.01%)}	_{302,578k (± 0.01%)}	_~	_302,539k	_302,637k	_{p=0.092 n=6}
_{Parse Time}	_{2.01s (± 0.77%)}	_{2.00s (± 0.42%)}	_~	_1.99s	_2.01s	_{p=0.078 n=6}
_{Bind Time}	_{1.00s (± 1.36%)}	_{1.00s (± 1.04%)}	_~	_0.98s	_1.01s	_{p=0.557 n=6}
_{Check Time}	_{6.26s (± 0.31%)}	_{6.27s (± 0.48%)}	_~	_6.24s	_6.32s	_{p=0.514 n=6}
_{Emit Time}	_{3.55s (± 0.58%)}	_{3.59s (± 0.45%)}	_{+0.03s (+ 0.94%)}	_3.56s	_3.60s	_{p=0.022 n=6}
_{Total Time}	_{12.83s (± 0.34%)}	_{12.85s (± 0.25%)}	_~	_12.82s	_12.91s	_{p=0.226 n=6}
_{material-ui - node (v18.15.0, x64)}
_{Memory used}	_{470,501k (± 0.00%)}	_{470,498k (± 0.00%)}	_~	_470,479k	_470,512k	_{p=0.423 n=6}
_{Parse Time}	_{2.58s (± 0.75%)}	_{2.58s (± 0.67%)}	_~	_2.56s	_2.60s	_{p=1.000 n=6}
_{Bind Time}	_{0.99s (± 0.55%)}	_{1.00s (± 0.89%)}	_~	_0.99s	_1.01s	_{p=0.341 n=6}
_{Check Time}	_{16.62s (± 0.34%)}	_{16.59s (± 0.36%)}	_~	_16.53s	_16.67s	_{p=0.421 n=6}
_{Emit Time}	_{0.00s (± 0.00%)}	_{0.00s (± 0.00%)}	_~	_0.00s	_0.00s	_{p=1.000 n=6}
_{Total Time}	_{20.20s (± 0.34%)}	_{20.17s (± 0.26%)}	_~	_20.11s	_20.25s	_{p=0.627 n=6}
_{xstate - node (v18.15.0, x64)}
_{Memory used}	_{512,610k (± 0.01%)}	_{512,649k (± 0.01%)}	_~	_512,579k	_512,720k	_{p=0.471 n=6}
_{Parse Time}	_{3.27s (± 0.30%)}	_{3.26s (± 0.27%)}	_~	_3.25s	_3.27s	_{p=0.082 n=6}
_{Bind Time}	_{1.55s (± 0.41%)}	_{1.55s (± 0.58%)}	_~	_1.54s	_1.56s	_{p=1.000 n=6}
_{Check Time}	_{2.86s (± 0.58%)}	_{2.88s (± 0.69%)}	_~	_2.86s	_2.91s	_{p=0.171 n=6}
_{Emit Time}	_{0.08s (± 4.99%)}	_{0.08s (± 0.00%)}	_~	_0.08s	_0.08s	_{p=0.405 n=6}
_{Total Time}	_{7.76s (± 0.28%)}	_{7.76s (± 0.26%)}	_~	_7.74s	_7.80s	_{p=0.935 n=6}

System info unknown

Hosts

node (v18.15.0, x64)

Scenarios

Angular - node (v18.15.0, x64)
Compiler-Unions - node (v18.15.0, x64)
Monaco - node (v18.15.0, x64)
TFS - node (v18.15.0, x64)
material-ui - node (v18.15.0, x64)
xstate - node (v18.15.0, x64)

_Benchmark	_Name	_Iterations
_Current	_pr	₆
_Baseline	_baseline	₆

tsserver

Comparison Report - baseline..pr

_Metric	_baseline	_pr	_Delta	_Best	_Worst	_p-value
_{Compiler-UnionsTSServer - node (v18.15.0, x64)}
_{Req 1 - updateOpen}	_{2,372ms (± 1.62%)}	_{2,393ms (± 1.42%)}	_~	_2,336ms	_2,423ms	_{p=0.229 n=6}
_{Req 2 - geterr}	_{5,376ms (± 1.70%)}	_{5,339ms (± 1.42%)}	_~	_5,282ms	_5,439ms	_{p=0.575 n=6}
_{Req 3 - references}	_{327ms (± 0.63%)}	_{330ms (± 1.71%)}	_~	_323ms	_337ms	_{p=0.375 n=6}
_{Req 4 - navto}	_{275ms (± 1.29%)}	_{276ms (± 1.27%)}	_~	_270ms	_280ms	_{p=0.627 n=6}
_{Req 5 - completionInfo count}	_{1,356 (± 0.00%)}	_{1,356 (± 0.00%)}	_~	_1,356	_1,356	_{p=1.000 n=6}
_{Req 5 - completionInfo}	_{83ms (± 7.98%)}	_{82ms (± 8.15%)}	_~	_76ms	_91ms	_{p=0.935 n=6}
_{CompilerTSServer - node (v18.15.0, x64)}
_{Req 1 - updateOpen}	_{2,474ms (± 0.99%)}	_{2,493ms (± 0.65%)}	_~	_2,466ms	_2,514ms	_{p=0.173 n=6}
_{Req 2 - geterr}	_{4,183ms (± 1.48%)}	_{4,106ms (± 1.96%)}	_~	_4,042ms	_4,210ms	_{p=0.173 n=6}
_{Req 3 - references}	_{334ms (± 1.14%)}	_{340ms (± 1.61%)}	_~	_333ms	_345ms	_{p=0.059 n=6}
_{Req 4 - navto}	_{283ms (± 0.48%)}	_{285ms (± 0.78%)}	_~	_283ms	_289ms	_{p=0.145 n=6}
_{Req 5 - completionInfo count}	_{1,518 (± 0.00%)}	_{1,518 (± 0.00%)}	_~	_1,518	_1,518	_{p=1.000 n=6}
_{Req 5 - completionInfo}	_{79ms (± 6.33%)}	_{82ms (± 8.53%)}	_~	_74ms	_89ms	_{p=0.546 n=6}
_{xstateTSServer - node (v18.15.0, x64)}
_{Req 1 - updateOpen}	_{2,598ms (± 0.38%)}	_{2,581ms (± 0.50%)}	_{-18ms (- 0.67%)}	_2,562ms	_2,598ms	_{p=0.045 n=6}
_{Req 2 - geterr}	_{1,711ms (± 2.24%)}	_{1,716ms (± 3.06%)}	_~	_1,638ms	_1,773ms	_{p=0.936 n=6}
_{Req 3 - references}	_{110ms (± 7.77%)}	_{113ms (±10.10%)}	_~	_105ms	_129ms	_{p=1.000 n=6}
_{Req 4 - navto}	_{359ms (± 0.37%)}	_{359ms (± 0.29%)}	_~	_358ms	_360ms	_{p=0.457 n=6}
_{Req 5 - completionInfo count}	_{2,073 (± 0.00%)}	_{2,073 (± 0.00%)}	_~	_2,073	_2,073	_{p=1.000 n=6}
_{Req 5 - completionInfo}	_{304ms (± 1.37%)}	_{308ms (± 1.32%)}	_~	_304ms	_315ms	_{p=0.126 n=6}

System info unknown

Hosts

node (v18.15.0, x64)

Scenarios

CompilerTSServer - node (v18.15.0, x64)
Compiler-UnionsTSServer - node (v18.15.0, x64)
xstateTSServer - node (v18.15.0, x64)

_Benchmark	_Name	_Iterations
_Current	_pr	₆
_Baseline	_baseline	₆

Startup

Comparison Report - baseline..pr

_Metric	_baseline	_pr	_Delta	_Best	_Worst	_p-value
_{tsc-startup - node (v18.15.0, x64)}
_{Execution time}	_{152.42ms (± 0.18%)}	_{152.45ms (± 0.16%)}	_~	_151.43ms	_155.17ms	_{p=0.282 n=600}
_{tsserver-startup - node (v18.15.0, x64)}
_{Execution time}	_{227.68ms (± 0.14%)}	_{227.71ms (± 0.15%)}	_~	_226.63ms	_231.04ms	_{p=0.891 n=600}
_{tsserverlibrary-startup - node (v18.15.0, x64)}
_{Execution time}	_{228.40ms (± 0.16%)}	_{228.55ms (± 0.19%)}	_{+0.15ms (+ 0.07%)}	_226.64ms	_235.53ms	_{p=0.001 n=600}
_{typescript-startup - node (v18.15.0, x64)}
_{Execution time}	_{228.80ms (± 0.18%)}	_{228.88ms (± 0.17%)}	_~	_227.25ms	_234.95ms	_{p=0.064 n=600}

System info unknown

Hosts

node (v18.15.0, x64)

Scenarios

tsc-startup - node (v18.15.0, x64)
tsserver-startup - node (v18.15.0, x64)
tsserverlibrary-startup - node (v18.15.0, x64)
typescript-startup - node (v18.15.0, x64)

_Benchmark	_Name	_Iterations
_Current	_pr	₆
_Baseline	_baseline	₆

Developer Information:

Download Benchmarks

jakebailey · 2023-10-23T20:19:45Z

tests/baselines/reference/callWithSpread.js

 var D = /** @class */ (function (_super) {
    __extends(D, _super);
    function D() {
        var _this = _super.call(this, 1, 2) || this;


Is it intentional to leave this unused variable behind? I guess it's harmless?

Yes and no. It's intentional in that the conditions for the simplification that elides var _this = isn't met. We could change the rules, in the future if necessary, but I don't want to spend too much time processing these simplifications during emit, which are primarily only to improve readability when debugging unmapped outputs, so I've generally opted for more coarse-grained rules.

rbuckton · 2023-10-23T21:41:37Z

I'm going to make a small update to make updatePropertyName public to align with #56194

typescript-bot · 2023-10-23T21:46:46Z

Looks like you're introducing a change to the public API surface area. If this includes breaking changes, please document them on our wiki's API Breaking Changes page.

Also, please make sure @DanielRosenwasser and @RyanCavanaugh are aware of the changes, just as a heads up.

… from other 'updateX' methods

more reliable mechanism for _this/_super simplification

21a697d

rbuckton requested review from andrewbranch and sandersn October 16, 2023 19:54

typescript-bot assigned rbuckton Oct 16, 2023

typescript-bot added Author: Team For Milestone Bug PRs that fix a bug with a specific milestone labels Oct 16, 2023

rbuckton requested review from DanielRosenwasser and jakebailey October 23, 2023 20:17

jakebailey approved these changes Oct 23, 2023

View reviewed changes

Expose 'updatePropertyName' in public NodeFactory API

8899b5a

Rename 'updatePropertyName' to 'replacePropertyName' to differentiate…

f1b9ce9

… from other 'updateX' methods

rbuckton force-pushed the fix-55646 branch from 189e45f to f1b9ce9 Compare October 23, 2023 21:52

rbuckton requested a review from RyanCavanaugh October 23, 2023 21:52

jakebailey approved these changes Oct 23, 2023

View reviewed changes

Merge branch 'main' into fix-55646

51ff38e

rbuckton merged commit 8e37e4b into main Oct 24, 2023

rbuckton deleted the fix-55646 branch October 24, 2023 01:01

microsoft locked as resolved and limited conversation to collaborators Oct 22, 2025

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