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GeezerVison is showing github.com — Fix issues + Support template literal types as discriminants by ahejlsberg · Pull Request #46137 · microsoft/TypeScript

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@ahejlsberg

@ahejlsberg Anders Hejlsberg (ahejlsberg) commented Sep 29, 2021

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Fixes #46045.
Fixes #46125.

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Anders Hejlsberg (ahejlsberg) added 2 commits September 29, 2021 13:42
@ahejlsberg
Fix issues + Support template literal types in discriminants
7f34792
@ahejlsberg
Add tests
e1907a2
@typescript-bot TypeScript Bot (typescript-bot) assigned Anders Hejlsberg (ahejlsberg) Sep 29, 2021
@typescript-bot TypeScript Bot (typescript-bot) added Author: Team For Milestone Bug PRs that fix a bug with a specific milestone labels Sep 29, 2021
@ahejlsberg
Anders Hejlsberg (ahejlsberg) requested review from Daniel Rosenwasser (DanielRosenwasser) and Andrew Branch (andrewbranch) September 29, 2021 20:58
weswigham
Wesley Wigham (weswigham) reviewed Sep 29, 2021
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Comment thread tests/baselines/reference/templateLiteralTypes3.js Outdated

// Repro from #46045

export type Action =

@weswigham Wesley Wigham (weswigham) Sep 29, 2021

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We probably want to remove the export from this and the other line to keep around the declaration emit in the test.

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@ahejlsberg Anders Hejlsberg (ahejlsberg) Sep 29, 2021

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Yeah, for sure.

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weswigham
Wesley Wigham (weswigham) reviewed Sep 29, 2021
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Comment thread src/compiler/checker.ts
const targetEnd = target.texts[target.texts.length - 1];
const startLen = Math.min(sourceStart.length, targetStart.length);
const endLen = Math.min(sourceEnd.length, targetEnd.length);
return sourceStart.slice(0, startLen) !== targetStart.slice(0, startLen) ||

@weswigham Wesley Wigham (weswigham) Sep 29, 2021

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Won't this flag foo-${boolean} and foo-${number} as possibly related? We still need to make sure the holes relate when this returns True, no?

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@ahejlsberg Anders Hejlsberg (ahejlsberg) Sep 29, 2021

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Yes, it'll flag them as possibly related. Or, rather, not flag them as definitely unrelated. We could potentially check the placeholders that immediately follow identical prefix texts or immediately precede identical suffix texts, but honestly there's very little gained from it. In fact, probably only the boolean vs. number disqualification. I think what is here already is sufficient, and it impacts whether we flag operands as non-overlapping, which isn't super critical to get 100% right.

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weswigham
Wesley Wigham (weswigham) reviewed Sep 29, 2021
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Comment thread tests/baselines/reference/templateLiteralTypes3.js Outdated

// Repro from #46125

function ff1<T extends string>(x: `foo-${string}`, y: `${string}-bar`, z: `baz-${string}`) {

@weswigham Wesley Wigham (weswigham) Sep 29, 2021

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Before I forget, can we also get a copy of this test with a signature like

function ff1<T extends string>(x: `foo-${T}`, y: `${T}-bar`, z: `baz-${T}`) {

? I figure it should behave the same, but, y'know, coverage. Maybe it can just be more cases on this signature, since it already has a generic parameter for some reason~

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@ahejlsberg Anders Hejlsberg (ahejlsberg) Sep 29, 2021

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Will do.

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@DanielRosenwasser

Daniel Rosenwasser (DanielRosenwasser) commented Sep 29, 2021

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TypeScript Bot (@typescript-bot) test this
TypeScript Bot (@typescript-bot) user test this
TypeScript Bot (@typescript-bot) perf test this
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TypeScript Bot (typescript-bot) commented Sep 29, 2021 •
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Heya Daniel Rosenwasser (@DanielRosenwasser), I've started to run the perf test suite on this PR at e1907a2. You can monitor the build here.

Update: The results are in!
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TypeScript Bot (typescript-bot) commented Sep 29, 2021 •
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Heya Daniel Rosenwasser (@DanielRosenwasser), I've started to run the extended test suite on this PR at e1907a2. You can monitor the build here.
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TypeScript Bot (typescript-bot) commented Sep 29, 2021 •
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Heya Daniel Rosenwasser (@DanielRosenwasser), I've started to run the parallelized community code test suite on this PR at e1907a2. You can monitor the build here.
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@ahejlsberg
Address CR feedback
955fda5
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Daniel Rosenwasser (@DanielRosenwasser)
The results of the perf run you requested are in!

Here they are:

Comparison Report - main..46137

Metric main 46137 Delta Best Worst
Angular - node (v10.16.3, x64)
Memory used 354,154k (± 0.02%) 354,131k (± 0.02%) -23k (- 0.01%) 354,015k 354,332k
Parse Time 1.94s (± 0.49%) 1.94s (± 0.37%) +0.01s (+ 0.36%) 1.93s 1.96s
Bind Time 0.84s (± 0.62%) 0.84s (± 0.98%) +0.00s (+ 0.36%) 0.83s 0.86s
Check Time 5.46s (± 0.46%) 5.47s (± 0.50%) +0.00s (+ 0.07%) 5.39s 5.52s
Emit Time 5.82s (± 0.33%) 5.86s (± 0.69%) +0.04s (+ 0.67%) 5.78s 5.96s
Total Time 14.06s (± 0.25%) 14.12s (± 0.33%) +0.05s (+ 0.38%) 14.01s 14.23s
Compiler-Unions - node (v10.16.3, x64)
Memory used 203,944k (± 0.02%) 203,852k (± 0.04%) -91k (- 0.04%) 203,701k 203,992k
Parse Time 0.78s (± 0.97%) 0.79s (± 1.13%) +0.00s (+ 0.26%) 0.77s 0.81s
Bind Time 0.52s (± 1.18%) 0.52s (± 1.28%) +0.00s (+ 0.38%) 0.51s 0.54s
Check Time 7.94s (± 0.70%) 7.91s (± 0.57%) -0.02s (- 0.29%) 7.82s 8.06s
Emit Time 2.47s (± 0.81%) 2.46s (± 0.81%) -0.01s (- 0.45%) 2.41s 2.50s
Total Time 11.71s (± 0.57%) 11.68s (± 0.42%) -0.03s (- 0.26%) 11.60s 11.82s
Monaco - node (v10.16.3, x64)
Memory used 342,054k (± 0.03%) 341,996k (± 0.02%) -58k (- 0.02%) 341,871k 342,258k
Parse Time 1.48s (± 0.51%) 1.47s (± 0.71%) -0.01s (- 0.34%) 1.44s 1.49s
Bind Time 0.75s (± 0.40%) 0.75s (± 0.77%) -0.00s (- 0.27%) 0.74s 0.76s
Check Time 5.45s (± 0.65%) 5.44s (± 0.63%) -0.01s (- 0.17%) 5.38s 5.53s
Emit Time 3.18s (± 0.69%) 3.19s (± 0.96%) +0.00s (+ 0.13%) 3.10s 3.25s
Total Time 10.86s (± 0.33%) 10.85s (± 0.36%) -0.01s (- 0.11%) 10.76s 10.94s
TFS - node (v10.16.3, x64)
Memory used 304,663k (± 0.02%) 304,672k (± 0.02%) +9k (+ 0.00%) 304,503k 304,836k
Parse Time 1.19s (± 0.50%) 1.19s (± 0.44%) -0.00s (- 0.25%) 1.18s 1.20s
Bind Time 0.71s (± 0.81%) 0.71s (± 0.78%) -0.00s (- 0.28%) 0.69s 0.72s
Check Time 4.99s (± 0.66%) 4.96s (± 0.46%) -0.03s (- 0.56%) 4.88s 5.00s
Emit Time 3.33s (± 1.65%) 3.33s (± 0.88%) -0.01s (- 0.21%) 3.26s 3.40s
Total Time 10.22s (± 0.61%) 10.18s (± 0.42%) -0.04s (- 0.40%) 10.05s 10.26s
material-ui - node (v10.16.3, x64)
Memory used 472,240k (± 0.02%) 472,270k (± 0.02%) +30k (+ 0.01%) 472,053k 472,392k
Parse Time 1.77s (± 0.38%) 1.76s (± 0.50%) -0.00s (- 0.23%) 1.75s 1.79s
Bind Time 0.66s (± 0.61%) 0.66s (± 0.55%) -0.00s (- 0.46%) 0.65s 0.66s
Check Time 14.41s (± 0.65%) 14.38s (± 0.71%) -0.03s (- 0.18%) 14.25s 14.68s
Emit Time 0.00s (± 0.00%) 0.00s (± 0.00%) 0.00s ( NaN%) 0.00s 0.00s
Total Time 16.83s (± 0.59%) 16.80s (± 0.64%) -0.03s (- 0.17%) 16.66s 17.12s
Angular - node (v12.1.0, x64)
Memory used 332,038k (± 0.03%) 331,993k (± 0.02%) -45k (- 0.01%) 331,833k 332,156k
Parse Time 1.93s (± 0.78%) 1.92s (± 0.45%) -0.00s (- 0.21%) 1.90s 1.93s
Bind Time 0.82s (± 0.82%) 0.81s (± 0.90%) -0.01s (- 0.61%) 0.80s 0.83s
Check Time 5.30s (± 0.37%) 5.30s (± 0.56%) -0.00s (- 0.06%) 5.23s 5.36s
Emit Time 6.09s (± 0.61%) 6.14s (± 0.89%) +0.04s (+ 0.72%) 6.06s 6.29s
Total Time 14.14s (± 0.39%) 14.18s (± 0.37%) +0.03s (+ 0.23%) 14.03s 14.30s
Compiler-Unions - node (v12.1.0, x64)
Memory used 191,331k (± 0.11%) 191,264k (± 0.12%) -66k (- 0.03%) 190,408k 191,506k
Parse Time 0.78s (± 0.85%) 0.78s (± 0.61%) -0.00s (- 0.38%) 0.77s 0.79s
Bind Time 0.53s (± 0.98%) 0.53s (± 0.92%) +0.00s (+ 0.95%) 0.52s 0.54s
Check Time 7.43s (± 0.66%) 7.39s (± 0.75%) -0.04s (- 0.54%) 7.30s 7.51s
Emit Time 2.46s (± 1.03%) 2.48s (± 0.95%) +0.02s (+ 0.69%) 2.43s 2.54s
Total Time 11.20s (± 0.61%) 11.18s (± 0.62%) -0.02s (- 0.21%) 11.06s 11.33s
Monaco - node (v12.1.0, x64)
Memory used 325,116k (± 0.02%) 325,088k (± 0.02%) -28k (- 0.01%) 324,925k 325,220k
Parse Time 1.45s (± 0.47%) 1.47s (± 0.81%) +0.01s (+ 0.89%) 1.44s 1.49s
Bind Time 0.73s (± 0.47%) 0.73s (± 1.06%) +0.00s (+ 0.55%) 0.72s 0.75s
Check Time 5.35s (± 0.65%) 5.31s (± 0.33%) -0.03s (- 0.58%) 5.27s 5.35s
Emit Time 3.20s (± 0.70%) 3.17s (± 0.65%) -0.03s (- 0.81%) 3.14s 3.22s
Total Time 10.73s (± 0.46%) 10.68s (± 0.36%) -0.04s (- 0.39%) 10.60s 10.77s
TFS - node (v12.1.0, x64)
Memory used 289,416k (± 0.02%) 289,429k (± 0.02%) +14k (+ 0.00%) 289,295k 289,617k
Parse Time 1.21s (± 0.71%) 1.21s (± 0.62%) +0.00s (+ 0.08%) 1.20s 1.23s
Bind Time 0.69s (± 0.69%) 0.69s (± 0.81%) +0.00s (+ 0.15%) 0.68s 0.70s
Check Time 4.90s (± 0.26%) 4.89s (± 0.31%) -0.02s (- 0.33%) 4.86s 4.94s
Emit Time 3.39s (± 0.85%) 3.38s (± 0.92%) -0.01s (- 0.35%) 3.31s 3.45s
Total Time 10.20s (± 0.33%) 10.17s (± 0.37%) -0.03s (- 0.25%) 10.08s 10.23s
material-ui - node (v12.1.0, x64)
Memory used 450,955k (± 0.02%) 450,742k (± 0.08%) -213k (- 0.05%) 449,797k 451,114k
Parse Time 1.77s (± 0.47%) 1.77s (± 0.57%) 0.00s ( 0.00%) 1.75s 1.80s
Bind Time 0.64s (± 1.32%) 0.64s (± 1.25%) +0.00s (+ 0.16%) 0.62s 0.66s
Check Time 13.05s (± 0.49%) 13.00s (± 0.68%) -0.05s (- 0.38%) 12.84s 13.26s
Emit Time 0.00s (± 0.00%) 0.00s (± 0.00%) 0.00s ( NaN%) 0.00s 0.00s
Total Time 15.47s (± 0.45%) 15.42s (± 0.58%) -0.05s (- 0.32%) 15.26s 15.67s
Angular - node (v14.15.1, x64)
Memory used 330,452k (± 0.01%) 330,452k (± 0.01%) -1k (- 0.00%) 330,419k 330,494k
Parse Time 1.95s (± 0.67%) 1.94s (± 0.49%) -0.00s (- 0.26%) 1.93s 1.97s
Bind Time 0.86s (± 0.65%) 0.86s (± 0.84%) +0.00s (+ 0.47%) 0.85s 0.88s
Check Time 5.35s (± 0.56%) 5.33s (± 0.58%) -0.02s (- 0.36%) 5.26s 5.40s
Emit Time 6.22s (± 0.74%) 6.20s (± 0.70%) -0.02s (- 0.32%) 6.10s 6.30s
Total Time 14.38s (± 0.51%) 14.33s (± 0.54%) -0.04s (- 0.29%) 14.19s 14.48s
Compiler-Unions - node (v14.15.1, x64)
Memory used 193,187k (± 0.01%) 192,529k (± 0.49%) -659k (- 0.34%) 189,961k 193,210k
Parse Time 0.81s (± 0.64%) 0.81s (± 0.90%) -0.00s (- 0.37%) 0.80s 0.83s
Bind Time 0.56s (± 0.65%) 0.55s (± 0.40%) -0.01s (- 0.90%) 0.55s 0.56s
Check Time 7.55s (± 0.73%) 7.49s (± 0.37%) -0.07s (- 0.86%) 7.41s 7.55s
Emit Time 2.41s (± 0.48%) 2.44s (± 1.14%) +0.04s (+ 1.45%) 2.39s 2.52s
Total Time 11.32s (± 0.50%) 11.29s (± 0.33%) -0.03s (- 0.26%) 11.21s 11.39s
Monaco - node (v14.15.1, x64)
Memory used 323,989k (± 0.00%) 323,996k (± 0.01%) +7k (+ 0.00%) 323,956k 324,046k
Parse Time 1.51s (± 0.51%) 1.51s (± 0.77%) -0.00s (- 0.20%) 1.48s 1.53s
Bind Time 0.76s (± 0.48%) 0.75s (± 0.79%) -0.00s (- 0.26%) 0.74s 0.77s
Check Time 5.30s (± 0.59%) 5.30s (± 0.49%) +0.00s (+ 0.02%) 5.25s 5.39s
Emit Time 3.21s (± 0.87%) 3.22s (± 0.81%) +0.02s (+ 0.50%) 3.18s 3.29s
Total Time 10.78s (± 0.45%) 10.79s (± 0.39%) +0.01s (+ 0.13%) 10.69s 10.89s
TFS - node (v14.15.1, x64)
Memory used 288,334k (± 0.01%) 288,337k (± 0.01%) +3k (+ 0.00%) 288,294k 288,407k
Parse Time 1.24s (± 0.47%) 1.23s (± 0.24%) -0.01s (- 0.73%) 1.22s 1.23s
Bind Time 0.73s (± 0.84%) 0.73s (± 0.55%) +0.00s (+ 0.00%) 0.72s 0.74s
Check Time 4.91s (± 0.38%) 4.93s (± 0.39%) +0.01s (+ 0.28%) 4.88s 4.97s
Emit Time 3.48s (± 0.52%) 3.49s (± 0.87%) +0.01s (+ 0.43%) 3.43s 3.56s
Total Time 10.36s (± 0.25%) 10.38s (± 0.31%) +0.02s (+ 0.19%) 10.31s 10.44s
material-ui - node (v14.15.1, x64)
Memory used 448,958k (± 0.09%) 449,300k (± 0.00%) +342k (+ 0.08%) 449,275k 449,351k
Parse Time 1.82s (± 0.61%) 1.81s (± 0.56%) -0.01s (- 0.49%) 1.79s 1.84s
Bind Time 0.68s (± 1.03%) 0.68s (± 0.69%) -0.00s (- 0.15%) 0.67s 0.69s
Check Time 13.23s (± 1.18%) 13.13s (± 0.55%) -0.10s (- 0.73%) 12.97s 13.36s
Emit Time 0.00s (± 0.00%) 0.00s (± 0.00%) 0.00s ( NaN%) 0.00s 0.00s
Total Time 15.73s (± 1.04%) 15.63s (± 0.52%) -0.11s (- 0.67%) 15.45s 15.89s
System
Machine Namets-ci-ubuntu
Platformlinux 4.4.0-210-generic
Architecturex64
Available Memory16 GB
Available Memory8 GB
CPUs4 × Intel(R) Core(TM) i7-4770 CPU @ 3.40GHz
Hosts
  • node (v10.16.3, x64)
  • node (v12.1.0, x64)
  • node (v14.15.1, x64)
Scenarios
  • Angular - node (v10.16.3, x64)
  • Angular - node (v12.1.0, x64)
  • Angular - node (v14.15.1, x64)
  • Compiler-Unions - node (v10.16.3, x64)
  • Compiler-Unions - node (v12.1.0, x64)
  • Compiler-Unions - node (v14.15.1, x64)
  • Monaco - node (v10.16.3, x64)
  • Monaco - node (v12.1.0, x64)
  • Monaco - node (v14.15.1, x64)
  • TFS - node (v10.16.3, x64)
  • TFS - node (v12.1.0, x64)
  • TFS - node (v14.15.1, x64)
  • material-ui - node (v10.16.3, x64)
  • material-ui - node (v12.1.0, x64)
  • material-ui - node (v14.15.1, x64)
Benchmark Name Iterations
Current 46137 10
Baseline main 10

Developer Information:

Download Benchmark
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@typescript-bot TypeScript Bot (typescript-bot) mentioned this pull request Sep 29, 2021
🤖 User test baselines have changed for fix46125 typescript-bot/TypeScript#207
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The user suite test run you requested has finished and failed. I've opened a PR with the baseline diff from master.
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@ahejlsberg

Anders Hejlsberg (ahejlsberg) commented Sep 29, 2021

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Tests look clean, perf is slightly improved if anything. I think this one is good to go!
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weswigham
Wesley Wigham (weswigham) approved these changes Sep 29, 2021
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andrewbranch
Andrew Branch (andrewbranch) approved these changes Sep 29, 2021
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@DanielRosenwasser
Daniel Rosenwasser (DanielRosenwasser) merged commit 5ec836d into main Sep 30, 2021
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Daniel Rosenwasser (DanielRosenwasser) deleted the fix46125 branch September 30, 2021 00:38
@DanielRosenwasser Daniel Rosenwasser (DanielRosenwasser) mentioned this pull request Sep 30, 2021
Design Meeting Notes, 9/29/2021 #46141
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@zardoy

Vitaly (zardoy) commented Oct 2, 2021

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Great! But will buitin string methods support this? For now, I'm forced to use these standalone functions:

const startsWith = <T extends string>(str: string, search: T): str is `${T}${string}` => str.startsWith(search);
const endsWith = <T extends string>(str: string, search: T): str is `${string}${T}` => str.endsWith(search);
const includes = <T extends string>(str: string, search: T): str is `${string}${T}${string}` => str.includes(search);
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@zardoy Vitaly (zardoy) mentioned this pull request Jan 31, 2022
feat: Improve startsWith, includes and endsWith typings for TS 4.5 selfrefactor/rambda#622
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@RyanCavanaugh Ryan Cavanaugh (RyanCavanaugh) mentioned this pull request Mar 22, 2024
Improve comparable relation of template literal types to detect more impossible situations #57872
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@Andarist Mateusz Burzyński (Andarist) mentioned this pull request Aug 5, 2025
Support contextual type discrimination based on template literal expressions #62203
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@microsoft Microsoft (microsoft) locked as resolved and limited conversation to collaborators Oct 21, 2025
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@weswigham Wesley Wigham (weswigham) weswigham approved these changes
@andrewbranch Andrew Branch (andrewbranch) andrewbranch approved these changes
@DanielRosenwasser Daniel Rosenwasser (DanielRosenwasser) Awaiting requested review from DanielRosenwasser

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@ahejlsberg Anders Hejlsberg (ahejlsberg)

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Successfully merging this pull request may close these issues.

Multiple issues with template literal type narrowing and relations Type narrowing on template literal types

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@ahejlsberg @DanielRosenwasser @typescript-bot @zardoy @weswigham @andrewbranch
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