Split heritage clause expression and type nodes by jakebailey · Pull Request #4797 · microsoft/typescript-go

Jake Bailey (jakebailey) · 2026-07-30T18:38:27Z

Gerrit Birkeland (@Gerrit0) mentioned on Discord that heritage clauses are expressions with type args, but that those are not marked as type nodes.

While we could probably restore the brand, that got me thinking whether or not we could actually just have two different nodes here depending on whether or not it's type space or not.

I threw copilot at it to see if it could make the change and how bad it'd be.

I actually don't think that this is that bad at all, ~~and does (IIRC) resolve a previous conversation we had about how it was weird to make the emitter handle this?~~ (no, that was something else, the use of ExprWithTypeArgs for hovers)

Jake Bailey (jakebailey) · 2026-07-30T20:33:07Z

TypeScript Bot (@typescript-bot) perf test this faster

typescript-automation · 2026-07-30T20:33:12Z

Starting jobs; this comment will be updated as builds start and complete.

Command	Status	Results
`perf test this faster`	✅ Started	👀 Results

Gerrit Birkeland (Gerrit0) · 2026-07-30T20:53:15Z

I guess this reinforces that there really are two cases here, which I hadn't really thought about previously, seems like a good idea!

Gerrit Birkeland (Gerrit0) · 2026-07-30T20:54:16Z

+            assert.strictEqual(interfaceDecl.heritageClauses?.[0].types[0].kind, SyntaxKind.TypeReference);
+        }
+        finally {
+            api.close();


This showing up all over in the unit tests makes me wonder if API ought to have a Symbol.dispose method so the tests can do using api = spawnAPI(...) and avoid this

typescript-automation · 2026-07-30T21:39:33Z

Jake Bailey (@jakebailey)
The results of the perf run you requested are in!

Here they are:

tsc

Comparison Report - baseline..pr

_Metric	_baseline	_pr	_Delta	_Best	_Worst	_p-value
_{Compiler-Unions - native}
_Errors	₄₁	₄₁	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_119,733	_119,733	_~	_~	_~	_{p=1.000 n=6}
_Types	_99,032	_99,032	_~	_~	_~	_{p=1.000 n=6}
_{Memory Used}	_{151,639k (± 1.02%)}	_{151,966k (± 0.82%)}	_~	_149,707k	_153,052k	_{p=0.589 n=6}
_{Memory Allocs}	_{2,275,827 (± 0.01%)}	_{2,274,896 (± 0.01%)}	_{-931 (- 0.04%)}	_2,274,695	_2,275,157	_{p=0.002 n=6}
_{Config Time}	_0.000s	_{0.000s (±154.76%)}	_~	_0.000s	_0.001s	_{p=0.455 n=6}
_{Parse Time}	_{0.056s (± 5.86%)}	_{0.057s (±14.97%)}	_~	_0.045s	_0.068s	_{p=0.781 n=6}
_{Bind Time}	_{0.019s (±32.41%)}	_{0.021s (±21.32%)}	_~	_0.016s	_0.028s	_{p=0.452 n=6}
_{Check Time}	_{0.756s (± 1.53%)}	_{0.758s (± 0.53%)}	_~	_0.754s	_0.764s	_{p=0.608 n=6}
_{Emit Time}	_{0.311s (± 4.24%)}	_{0.302s (± 2.36%)}	_~	_0.293s	_0.310s	_{p=0.162 n=6}
_{Total Time}	_{1.152s (± 0.66%)}	_{1.143s (± 1.60%)}	_~	_1.126s	_1.169s	_{p=0.310 n=6}
_{angular-1 - native}
_Errors	₃	₃	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_{873,222 (± 0.07%)}	_{871,729 (± 0.09%)}	_{-1,493 (- 0.17%)}	_870,620	_872,986	_{p=0.004 n=6}
_Types	_{263,962 (± 0.00%)}	_{263,962 (± 0.00%)}	_~	_263,960	_263,963	_{p=1.000 n=6}
_{Memory Used}	_{808,238k (± 0.07%)}	_{807,699k (± 0.12%)}	_~	_806,999k	_809,599k	_{p=0.132 n=6}
_{Memory Allocs}	_{13,163,875 (± 0.16%)}	_{13,148,472 (± 0.10%)}	_~	_13,135,959	_13,164,939	_{p=0.310 n=6}
_{Config Time}	_0.017s	_{0.017s (± 2.98%)}	_~	_0.017s	_0.018s	_{p=0.455 n=6}
_{Parse Time}	_{0.237s (± 5.01%)}	_{0.232s (± 3.81%)}	_~	_0.223s	_0.247s	_{p=0.485 n=6}
_{Bind Time}	_{0.060s (±38.87%)}	_{0.059s (±34.25%)}	_~	_0.040s	_0.085s	_{p=0.619 n=6}
_{Check Time}	_0s	_0s	_~	_~	_~	_{p=1.000 n=6}
_{Emit Time}	_{1.871s (± 1.27%)}	_{1.894s (± 1.55%)}	_~	_1.859s	_1.934s	_{p=0.368 n=6}
_{Total Time}	_{2.194s (± 1.27%)}	_{2.214s (± 0.70%)}	_~	_2.197s	_2.237s	_{p=0.197 n=6}
_{mui-docs - native}
_Errors	_{11,273 (± 0.06%)}	_{11,278 (± 0.06%)}	_~	_11,265	_11,282	_{p=0.405 n=6}
_Symbols	_4,386,587	_4,386,587	_~	_~	_~	_{p=1.000 n=6}
_Types	_1,537,077	_1,537,077	_~	_~	_~	_{p=1.000 n=6}
_{Memory Used}	_{4,961,388k (± 0.05%)}	_{4,961,035k (± 0.04%)}	_~	_4,958,852k	_4,963,130k	_{p=0.818 n=6}
_{Memory Allocs}	_{45,981,123 (± 0.09%)}	_{45,974,343 (± 0.06%)}	_~	_45,941,030	_46,021,422	_{p=0.818 n=6}
_{Config Time}	_{0.016s (± 2.52%)}	_{0.018s (± 8.97%)}	_~	_0.016s	_0.020s	_{p=0.061 n=6}
_{Parse Time}	_{0.494s (± 5.29%)}	_{0.504s (± 1.66%)}	_~	_0.498s	_0.521s	_{p=0.524 n=6}
_{Bind Time}	_0.002s	_0.002s	_~	_~	_~	_{p=1.000 n=6}
_{Check Time}	_{16.022s (± 0.42%)}	_{15.979s (± 0.26%)}	_~	_15.903s	_16.024s	_{p=0.394 n=6}
_{Emit Time}	_{0.456s (± 3.26%)}	_{0.454s (± 3.13%)}	_~	_0.447s	_0.483s	_{p=0.398 n=6}
_{Total Time}	_{17.729s (± 0.31%)}	_{17.696s (± 0.46%)}	_~	_17.556s	_17.806s	_{p=0.699 n=6}
_{self-build-src - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_1,394,491	_1,394,491	_~	_~	_~	_{p=1.000 n=6}
_Types	_442,212	_442,212	_~	_~	_~	_{p=1.000 n=6}
_{Memory Used}	_{1,591,342k (± 0.13%)}	_{1,592,506k (± 0.31%)}	_~	_1,582,873k	_1,595,993k	_{p=0.240 n=6}
_{Memory Allocs}	_{97,098,657 (± 0.05%)}	_{97,024,074 (± 0.04%)}	_{-74,583 (- 0.08%)}	_96,967,778	_97,067,133	_{p=0.026 n=6}
_{Config Time}	_{0.017s (±18.16%)}	_{0.015s (±20.20%)}	_~	_0.011s	_0.019s	_{p=0.331 n=6}
_{Parse Time}	_{0.235s (± 2.20%)}	_{0.231s (± 1.21%)}	_~	_0.228s	_0.236s	_{p=0.171 n=6}
_{Bind Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=6}
_{Check Time}	_{2.161s (± 0.39%)}	_{2.146s (± 0.60%)}	_{-0.015s (- 0.71%)}	_2.124s	_2.157s	_{p=0.041 n=6}
_{Emit Time}	_{0.294s (± 3.58%)}	_{0.301s (± 2.53%)}	_~	_0.289s	_0.310s	_{p=0.258 n=6}
_{Total Time}	_{28.472s (± 0.45%)}	_{28.476s (± 0.44%)}	_~	_28.344s	_28.674s	_{p=0.699 n=6}
_{self-compiler - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_337,834	_337,834	_~	_~	_~	_{p=1.000 n=6}
_Types	_199,561	_199,561	_~	_~	_~	_{p=1.000 n=6}
_{Memory Used}	_{318,861k (± 0.03%)}	_{318,829k (± 0.04%)}	_~	_318,641k	_318,936k	_{p=0.485 n=6}
_{Memory Allocs}	_{4,678,563 (± 0.01%)}	_{4,675,943 (± 0.01%)}	_{-2,620 (- 0.06%)}	_4,674,841	_4,676,730	_{p=0.002 n=6}
_{Config Time}	_0.001s	_0.001s	_~	_~	_~	_{p=1.000 n=6}
_{Parse Time}	_{0.117s (± 3.19%)}	_{0.116s (± 5.19%)}	_~	_0.107s	_0.123s	_{p=0.848 n=6}
_{Bind Time}	_{0.000s (±244.70%)}	_0.000s	_~	_~	_~	_{p=1.000 n=6}
_{Check Time}	_{1.272s (± 0.61%)}	_{1.265s (± 0.55%)}	_{-0.007s (- 0.56%)}	_1.256s	_1.277s	_{p=0.048 n=6}
_{Emit Time}	_{0.120s (± 7.97%)}	_{0.120s (± 6.68%)}	_~	_0.108s	_0.129s	_{p=0.970 n=6}
_{Total Time}	_{1.563s (± 0.42%)}	_{1.558s (± 0.63%)}	_~	_1.545s	_1.575s	_{p=0.327 n=6}
_{ts-pre-modules - native}
_Errors	₈₇	₈₇	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_302,246	_302,246	_~	_~	_~	_{p=1.000 n=6}
_Types	_181,595	_181,595	_~	_~	_~	_{p=1.000 n=6}
_{Memory Used}	_{274,832k (± 0.02%)}	_{274,797k (± 0.02%)}	_~	_274,711k	_274,883k	_{p=0.394 n=6}
_{Memory Allocs}	_{1,675,501 (± 0.02%)}	_{1,675,645 (± 0.02%)}	_~	_1,675,294	_1,676,218	_{p=0.394 n=6}
_{Config Time}	_0.001s	_0.001s	_~	_~	_~	_{p=1.000 n=6}
_{Parse Time}	_{0.099s (± 4.52%)}	_{0.102s (± 4.42%)}	_~	_0.096s	_0.106s	_{p=0.675 n=6}
_{Bind Time}	_{0.038s (±11.58%)}	_{0.041s (± 7.06%)}	_~	_0.037s	_0.045s	_{p=0.381 n=6}
_{Check Time}	_{1.077s (± 2.06%)}	_{1.058s (± 0.63%)}	_~	_1.048s	_1.066s	_{p=0.084 n=6}
_{Emit Time}	_0.000s	_0.000s	_~	_~	_~	_{p=1.000 n=6}
_{Total Time}	_{1.231s (± 1.71%)}	_{1.216s (± 0.54%)}	_~	_1.206s	_1.225s	_{p=0.223 n=6}
_{vscode - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_7,522,360	_7,522,360	_~	_~	_~	_{p=1.000 n=6}
_Types	_2,622,244	_2,622,244	_~	_~	_~	_{p=1.000 n=6}
_{Memory Used}	_{5,026,703k (± 0.04%)}	_{5,025,949k (± 0.01%)}	_~	_5,025,241k	_5,027,131k	_{p=0.937 n=6}
_{Memory Allocs}	_{38,401,982 (± 0.07%)}	_{38,383,024 (± 0.04%)}	_~	_38,368,487	_38,411,193	_{p=0.180 n=6}
_{Config Time}	_{0.076s (±10.49%)}	_{0.077s (± 7.34%)}	_~	_0.070s	_0.084s	_{p=0.574 n=6}
_{Parse Time}	_{0.906s (± 3.45%)}	_{0.902s (± 4.39%)}	_~	_0.871s	_0.973s	_{p=0.589 n=6}
_{Bind Time}	_{0.211s (±22.45%)}	_{0.207s (±25.06%)}	_~	_0.164s	_0.297s	_{p=1.000 n=6}
_{Check Time}	_{8.719s (± 1.00%)}	_{8.754s (± 1.25%)}	_~	_8.615s	_8.901s	_{p=0.589 n=6}
_{Emit Time}	_{2.389s (± 9.35%)}	_{2.376s (±10.62%)}	_~	_2.159s	_2.704s	_{p=0.786 n=6}
_{Total Time}	_{12.334s (± 1.00%)}	_{12.343s (± 1.22%)}	_~	_12.218s	_12.540s	_{p=1.000 n=6}
_{webpack - native}
_Errors	₂	₂	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_195,834	_195,834	_~	_~	_~	_{p=1.000 n=6}
_Types	₃₄₀	₃₄₀	_~	_~	_~	_{p=1.000 n=6}
_{Memory Used}	_{229,821k (± 0.13%)}	_{230,036k (± 0.10%)}	_~	_229,718k	_230,329k	_{p=0.240 n=6}
_{Memory Allocs}	_{980,682 (± 0.65%)}	_{982,434 (± 0.59%)}	_~	_974,772	_987,779	_{p=0.589 n=6}
_{Config Time}	_{0.011s (±25.69%)}	_{0.012s (±22.95%)}	_~	_0.009s	_0.016s	_{p=0.597 n=6}
_{Parse Time}	_{0.152s (± 2.60%)}	_{0.155s (± 3.49%)}	_~	_0.147s	_0.163s	_{p=0.177 n=6}
_{Bind Time}	_0s	_0s	_~	_~	_~	_{p=1.000 n=6}
_{Check Time}	_0s	_0s	_~	_~	_~	_{p=1.000 n=6}
_{Emit Time}	_{0.053s (±13.83%)}	_{0.041s (±10.43%)}	_{🟩-0.012s (-23.20%)}	_0.034s	_0.044s	_{p=0.026 n=6}
_{Total Time}	_{0.217s (± 2.27%)}	_{0.209s (± 2.65%)}	_{🟩-0.008s (- 3.54%)}	_0.202s	_0.215s	_{p=0.024 n=6}
_{xstate-main - native}
_Errors	₀	₀	_~	_~	_~	_{p=1.000 n=6}
_Symbols	_1,066,055	_1,066,055	_~	_~	_~	_{p=1.000 n=6}
_Types	_392,847	_392,847	_~	_~	_~	_{p=1.000 n=6}
_{Memory Used}	_{634,739k (± 0.02%)}	_{634,761k (± 0.02%)}	_~	_634,636k	_635,003k	_{p=0.818 n=6}
_{Memory Allocs}	_{5,000,448 (± 0.12%)}	_{5,007,061 (± 0.17%)}	_~	_4,995,905	_5,018,737	_{p=0.180 n=6}
_{Config Time}	_{0.005s (±17.48%)}	_{0.004s (±27.36%)}	_~	_0.003s	_0.005s	_{p=0.545 n=6}
_{Parse Time}	_{0.126s (± 4.66%)}	_{0.123s (± 3.72%)}	_~	_0.116s	_0.128s	_{p=0.582 n=6}
_{Bind Time}	_{0.040s (±24.70%)}	_{0.034s (±29.47%)}	_~	_0.024s	_0.047s	_{p=0.193 n=6}
_{Check Time}	_{1.246s (± 1.47%)}	_{1.231s (± 0.68%)}	_~	_1.220s	_1.244s	_{p=0.190 n=6}
_{Emit Time}	_0.001s	_0.001s	_~	_~	_~	_{p=1.000 n=6}
_{Total Time}	_{1.420s (± 1.07%)}	_{1.397s (± 0.67%)}	_{-0.023s (- 1.63%)}	_1.378s	_1.403s	_{p=0.028 n=6}

System info unknown

Hosts

native

Scenarios

Compiler-Unions - native
angular-1 - native
mui-docs - native
self-build-src - native
self-compiler - native
ts-pre-modules - native
vscode - native
webpack - native
xstate-main - native

_Benchmark	_Name	_Iterations
_Current	_pr	₆
_Baseline	_baseline	₆

Developer Information:

Download Benchmarks

Andrew Branch (andrewbranch) · 2026-08-03T15:17:09Z

 	p.emitToken(node.Token, node.Pos(), WriteKindKeyword, node.AsNode())
 	p.writeSpace()
-	p.emitList((*Printer).emitExpressionWithTypeArgumentsNode, node.AsNode(), node.Types, LFHeritageClauseTypes)
+	p.emitList((*Printer).emitTypeNodeOutsideExtends, node.AsNode(), node.Types, LFHeritageClauseTypes)


This reads kind of suspiciously both before and after, doesn’t it? Because an ExpressionWithTypeArguments is not a type node, and a type reference is not an ExpressionWithTypeArguments?

Split heritage clause expression and type nodes

75f021b

Gerrit Birkeland (Gerrit0) reviewed Jul 30, 2026

View reviewed changes

Jake Bailey (jakebailey) requested review from Anders Hejlsberg (ahejlsberg), Andrew Branch (andrewbranch) and Wesley Wigham (weswigham) July 30, 2026 20:55

Andrew Branch (andrewbranch) reviewed Aug 3, 2026

View reviewed changes

Jake Bailey (jakebailey) added 3 commits August 7, 2026 15:07

Handle heritage clause element kinds in printer

26f52fb

Use heritage clause element types in helpers

e865a77

Use type-space semantics for heritage references

a36ce60

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Split heritage clause expression and type nodes - #4797

Split heritage clause expression and type nodes#4797
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