In #45025 we increased the type instantiation depth limit from 50 to 500. We've subsequently seen multiple examples of stack overflows occurring during compilation of programs containing non-terminating types, particularly when the compiler is used in browser hosted environments (where, apparently, in some cases the call stack limit is lower than in Node.js). It is clear that 500 is too high of a limit, so in this PR we lower the maximum to 100.

There are legitimate cases where evaluation of recursive conditional types needs more than 100 iterations to complete. For that reason, this PR implements tail recursive evaluation of conditional types. Specifically, when a conditional type ends in another (or, through recursion, another instantiation of the same) conditional type, the compiler now performs type resolution in a loop that consumes no extra call stack. We permit evaluation of such types to loop 1000 times before we consider the type non-terminating and issue an error.

The following conditional type is tail recursive:

type Trim<S extends string> =
    S extends ` ${infer T}` ? Trim<T> :
    S extends `${infer T} ` ? Trim<T> :
    S;

Previously, resolution of instantiations of this type would error for string literals containing more than 25 blanks. We now permit strings with up to 1000 blanks.

Conditional types that aren't tail recursive generally can be written in a tail recursive form by introducing an "accumulator". For example, this type, which extracts a union of the characters in a string, isn't tail recursive (because it recurs through a union type)

type GetChars<S> =
    S extends `${infer Char}${infer Rest}` ? Char | GetChars<Rest> : never;

but this rewritten form is

type GetChars<S> = GetCharsRec<S, never>;
type GetCharsRec<S, Acc> =
    S extends `${infer Char}${infer Rest}` ? GetCharsRec<Rest, Char | Acc> : Acc;

Some additional examples of tail recursive conditional types:

type Reverse<T> = any[] extends T ? T : ReverseRec<T, []>;
type ReverseRec<T, Acc extends unknown[]> =
    T extends [infer Head, ...infer Tail] ? ReverseRec<Tail, [Head, ...Acc]> : Acc;

type T1 = Reverse<[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9]>;

type TupleOf<T, N extends number> = number extends N ? T[] : TupleOfRec<T, N, []>;
type TupleOfRec<T, N extends number, Acc extends unknown[]> =
    Acc["length"] extends N ? Acc : TupleOfRec<T, N, [T, ...Acc]>;

type T2 = TupleOf<any, 200>;

The examples above previously would error in "Type instantiation is excessively deep and possibly infinite", but now succeed.

@typescript-bot test this
@typescript-bot user test this
@typescript-bot run dt
@typescript-bot perf test this

Heya @ahejlsberg, I've started to run the parallelized Definitely Typed test suite on this PR at 093f76a. You can monitor the build here.

Heya @ahejlsberg, I've started to run the extended test suite on this PR at 093f76a. You can monitor the build here.

Heya @ahejlsberg, I've started to run the parallelized community code test suite on this PR at 093f76a. You can monitor the build here.

Heya @ahejlsberg, I've started to run the perf test suite on this PR at 093f76a. You can monitor the build here.

Update: The results are in!

It'd be nice if we could kinda automatically do the "extract to an accumulator" thing you suggest in the OP, so people didn't need to write their conditionals with such structure in mind; but this seems good.

The user suite test run you requested has finished and failed. I've opened a PR with the baseline diff from master.

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

Here they are:

Comparison Report - main..45711

Metric	main	45711	Delta	Best	Worst
Angular - node (v10.16.3, x64)
Memory used	351,611k (± 0.03%)	351,552k (± 0.02%)	-59k (- 0.02%)	351,375k	351,666k
Parse Time	1.91s (± 0.30%)	1.90s (± 0.49%)	-0.00s (- 0.26%)	1.88s	1.92s
Bind Time	0.85s (± 0.40%)	0.85s (± 0.70%)	+0.00s (+ 0.23%)	0.84s	0.87s
Check Time	5.39s (± 0.41%)	5.40s (± 0.32%)	+0.01s (+ 0.15%)	5.36s	5.43s
Emit Time	5.83s (± 0.42%)	5.84s (± 0.45%)	+0.01s (+ 0.17%)	5.79s	5.91s
Total Time	13.97s (± 0.25%)	13.99s (± 0.27%)	+0.02s (+ 0.11%)	13.93s	14.10s
Compiler-Unions - node (v10.16.3, x64)
Memory used	203,474k (± 0.03%)	203,450k (± 0.03%)	-24k (- 0.01%)	203,353k	203,620k
Parse Time	0.78s (± 0.85%)	0.78s (± 0.87%)	+0.00s (+ 0.51%)	0.77s	0.80s
Bind Time	0.52s (± 1.13%)	0.52s (± 1.28%)	-0.00s (- 0.19%)	0.51s	0.54s
Check Time	7.82s (± 0.42%)	7.80s (± 0.42%)	-0.02s (- 0.26%)	7.75s	7.91s
Emit Time	2.44s (± 0.51%)	2.43s (± 1.06%)	-0.01s (- 0.25%)	2.40s	2.53s
Total Time	11.56s (± 0.42%)	11.54s (± 0.39%)	-0.02s (- 0.15%)	11.47s	11.65s
Monaco - node (v10.16.3, x64)
Memory used	340,659k (± 0.02%)	340,634k (± 0.02%)	-25k (- 0.01%)	340,472k	340,811k
Parse Time	1.45s (± 0.69%)	1.45s (± 0.67%)	+0.00s (+ 0.07%)	1.43s	1.47s
Bind Time	0.75s (± 0.87%)	0.75s (± 0.40%)	0.00s ( 0.00%)	0.74s	0.75s
Check Time	5.44s (± 0.37%)	5.40s (± 0.45%)	-0.04s (- 0.68%)	5.36s	5.48s
Emit Time	3.17s (± 0.78%)	3.15s (± 0.58%)	-0.02s (- 0.63%)	3.11s	3.18s
Total Time	10.80s (± 0.32%)	10.75s (± 0.34%)	-0.05s (- 0.50%)	10.67s	10.82s
TFS - node (v10.16.3, x64)
Memory used	304,028k (± 0.01%)	304,024k (± 0.03%)	-4k (- 0.00%)	303,780k	304,176k
Parse Time	1.18s (± 0.52%)	1.19s (± 0.57%)	+0.01s (+ 0.59%)	1.18s	1.21s
Bind Time	0.72s (± 0.95%)	0.71s (± 1.06%)	-0.00s (- 0.14%)	0.70s	0.73s
Check Time	4.92s (± 0.56%)	4.94s (± 0.62%)	+0.03s (+ 0.53%)	4.86s	4.99s
Emit Time	3.31s (± 1.05%)	3.37s (± 1.96%)	+0.06s (+ 1.72%)	3.25s	3.52s
Total Time	10.12s (± 0.45%)	10.21s (± 0.71%)	+0.09s (+ 0.86%)	10.08s	10.40s
material-ui - node (v10.16.3, x64)
Memory used	469,942k (± 0.01%)	469,793k (± 0.01%)	-149k (- 0.03%)	469,715k	469,940k
Parse Time	1.73s (± 0.40%)	1.73s (± 0.43%)	+0.01s (+ 0.46%)	1.72s	1.75s
Bind Time	0.66s (± 0.55%)	0.67s (± 0.51%)	+0.01s (+ 1.36%)	0.67s	0.68s
Check Time	14.15s (± 0.27%)	14.35s (± 0.65%)	+0.20s (+ 1.43%)	14.16s	14.60s
Emit Time	0.00s (± 0.00%)	0.00s (± 0.00%)	0.00s ( NaN%)	0.00s	0.00s
Total Time	16.54s (± 0.24%)	16.76s (± 0.58%)	+0.22s (+ 1.31%)	16.56s	17.01s
Angular - node (v12.1.0, x64)
Memory used	329,584k (± 0.03%)	329,534k (± 0.02%)	-49k (- 0.01%)	329,365k	329,668k
Parse Time	1.88s (± 0.62%)	1.88s (± 0.48%)	-0.00s (- 0.21%)	1.85s	1.89s
Bind Time	0.83s (± 0.44%)	0.84s (± 0.80%)	+0.00s (+ 0.24%)	0.82s	0.85s
Check Time	5.22s (± 0.52%)	5.22s (± 0.39%)	+0.01s (+ 0.10%)	5.19s	5.28s
Emit Time	6.05s (± 0.49%)	6.13s (± 1.46%)	+0.08s (+ 1.32%)	6.04s	6.47s
Total Time	13.98s (± 0.31%)	14.07s (± 0.71%)	+0.08s (+ 0.59%)	13.94s	14.41s
Compiler-Unions - node (v12.1.0, x64)
Memory used	191,013k (± 0.02%)	190,985k (± 0.03%)	-28k (- 0.01%)	190,894k	191,166k
Parse Time	0.78s (± 0.83%)	0.78s (± 0.88%)	-0.01s (- 0.77%)	0.76s	0.79s
Bind Time	0.52s (± 1.13%)	0.53s (± 1.09%)	+0.01s (+ 1.15%)	0.52s	0.54s
Check Time	7.37s (± 0.58%)	7.39s (± 0.72%)	+0.02s (+ 0.22%)	7.31s	7.50s
Emit Time	2.47s (± 1.18%)	2.45s (± 0.78%)	-0.02s (- 0.61%)	2.42s	2.51s
Total Time	11.15s (± 0.49%)	11.15s (± 0.57%)	0.00s ( 0.00%)	11.04s	11.28s
Monaco - node (v12.1.0, x64)
Memory used	323,734k (± 0.01%)	323,779k (± 0.02%)	+45k (+ 0.01%)	323,576k	323,859k
Parse Time	1.43s (± 0.51%)	1.43s (± 0.85%)	+0.00s (+ 0.21%)	1.41s	1.46s
Bind Time	0.72s (± 0.47%)	0.73s (± 0.92%)	+0.00s (+ 0.55%)	0.71s	0.74s
Check Time	5.26s (± 0.43%)	5.28s (± 0.37%)	+0.03s (+ 0.49%)	5.23s	5.31s
Emit Time	3.19s (± 0.67%)	3.19s (± 0.78%)	-0.00s (- 0.06%)	3.15s	3.25s
Total Time	10.60s (± 0.35%)	10.63s (± 0.30%)	+0.03s (+ 0.30%)	10.54s	10.69s
TFS - node (v12.1.0, x64)
Memory used	288,714k (± 0.02%)	288,785k (± 0.02%)	+71k (+ 0.02%)	288,664k	288,910k
Parse Time	1.20s (± 0.77%)	1.21s (± 0.93%)	+0.01s (+ 0.75%)	1.19s	1.24s
Bind Time	0.70s (± 0.71%)	0.70s (± 0.97%)	+0.01s (+ 1.29%)	0.69s	0.72s
Check Time	4.83s (± 0.41%)	4.87s (± 0.53%)	+0.04s (+ 0.81%)	4.82s	4.92s
Emit Time	3.37s (± 0.55%)	3.40s (± 0.83%)	+0.03s (+ 0.77%)	3.34s	3.48s
Total Time	10.10s (± 0.32%)	10.18s (± 0.55%)	+0.08s (+ 0.82%)	10.05s	10.34s
material-ui - node (v12.1.0, x64)
Memory used	448,462k (± 0.07%)	448,419k (± 0.05%)	-43k (- 0.01%)	447,608k	448,684k
Parse Time	1.72s (± 0.47%)	1.73s (± 0.50%)	+0.00s (+ 0.29%)	1.71s	1.75s
Bind Time	0.65s (± 0.86%)	0.65s (± 0.91%)	+0.01s (+ 0.93%)	0.64s	0.67s
Check Time	12.78s (± 0.53%)	12.97s (± 0.89%)	+0.19s (+ 1.50%)	12.76s	13.24s
Emit Time	0.00s (± 0.00%)	0.00s (± 0.00%)	0.00s ( NaN%)	0.00s	0.00s
Total Time	15.15s (± 0.46%)	15.36s (± 0.78%)	+0.20s (+ 1.34%)	15.16s	15.63s
Angular - node (v14.15.1, x64)
Memory used	328,115k (± 0.01%)	328,111k (± 0.01%)	-4k (- 0.00%)	328,022k	328,206k
Parse Time	1.91s (± 0.70%)	1.90s (± 0.52%)	-0.01s (- 0.37%)	1.88s	1.92s
Bind Time	0.88s (± 1.13%)	0.88s (± 0.41%)	+0.00s (+ 0.45%)	0.88s	0.89s
Check Time	5.29s (± 0.46%)	5.28s (± 0.47%)	-0.01s (- 0.13%)	5.21s	5.33s
Emit Time	6.22s (± 0.87%)	6.22s (± 0.78%)	-0.01s (- 0.10%)	6.12s	6.30s
Total Time	14.30s (± 0.55%)	14.29s (± 0.49%)	-0.02s (- 0.11%)	14.11s	14.39s
Compiler-Unions - node (v14.15.1, x64)
Memory used	192,165k (± 0.48%)	192,487k (± 0.38%)	+321k (+ 0.17%)	189,506k	192,910k
Parse Time	0.81s (± 0.76%)	0.81s (± 0.58%)	+0.00s (+ 0.12%)	0.80s	0.82s
Bind Time	0.55s (± 1.08%)	0.56s (± 0.53%)	+0.00s (+ 0.54%)	0.55s	0.56s
Check Time	7.50s (± 0.50%)	7.54s (± 0.71%)	+0.04s (+ 0.52%)	7.42s	7.65s
Emit Time	2.45s (± 0.58%)	2.46s (± 0.56%)	+0.01s (+ 0.45%)	2.43s	2.49s
Total Time	11.31s (± 0.44%)	11.37s (± 0.50%)	+0.06s (+ 0.51%)	11.26s	11.52s
Monaco - node (v14.15.1, x64)
Memory used	322,544k (± 0.00%)	322,548k (± 0.01%)	+4k (+ 0.00%)	322,489k	322,578k
Parse Time	1.49s (± 0.98%)	1.49s (± 0.61%)	+0.00s (+ 0.27%)	1.47s	1.51s
Bind Time	0.75s (± 0.40%)	0.76s (± 0.66%)	+0.00s (+ 0.40%)	0.75s	0.77s
Check Time	5.21s (± 0.61%)	5.24s (± 0.27%)	+0.03s (+ 0.58%)	5.22s	5.28s
Emit Time	3.22s (± 0.63%)	3.22s (± 0.65%)	0.00s ( 0.00%)	3.16s	3.26s
Total Time	10.67s (± 0.46%)	10.71s (± 0.27%)	+0.04s (+ 0.34%)	10.61s	10.75s
TFS - node (v14.15.1, x64)
Memory used	287,699k (± 0.01%)	287,695k (± 0.00%)	-5k (- 0.00%)	287,669k	287,707k
Parse Time	1.26s (± 1.13%)	1.25s (± 2.11%)	-0.01s (- 0.48%)	1.21s	1.34s
Bind Time	0.72s (± 0.80%)	0.76s (± 4.49%)	+0.04s (+ 5.28%)	0.71s	0.83s
Check Time	4.86s (± 0.54%)	4.87s (± 0.68%)	+0.01s (+ 0.14%)	4.79s	4.92s
Emit Time	3.46s (± 1.01%)	3.46s (± 0.88%)	-0.00s (- 0.14%)	3.40s	3.53s
Total Time	10.30s (± 0.40%)	10.34s (± 0.60%)	+0.03s (+ 0.33%)	10.20s	10.44s
material-ui - node (v14.15.1, x64)
Memory used	447,023k (± 0.00%)	446,915k (± 0.01%)	-108k (- 0.02%)	446,870k	446,976k
Parse Time	1.76s (± 0.47%)	1.77s (± 0.62%)	+0.02s (+ 0.97%)	1.75s	1.80s
Bind Time	0.68s (± 0.87%)	0.69s (± 0.94%)	+0.01s (+ 1.02%)	0.68s	0.71s
Check Time	12.90s (± 0.53%)	13.19s (± 0.49%)	+0.29s (+ 2.27%)	13.00s	13.34s
Emit Time	0.00s (± 0.00%)	0.00s (± 0.00%)	0.00s ( NaN%)	0.00s	0.00s
Total Time	15.34s (± 0.50%)	15.66s (± 0.42%)	+0.32s (+ 2.09%)	15.47s	15.78s

System

Machine Name	ts-ci-ubuntu
Platform	linux 4.4.0-210-generic
Architecture	x64
Available Memory	16 GB
Available Memory	9 GB
CPUs	4 × 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	45711	10
Baseline	main	10

Developer Information:

Download Benchmark

I can't tell how much of this in the noise, but the check time on material-ui does seem like it's taken a hit across all versions.

@typescript-bot perf test this

Heya @ahejlsberg, I've started to run the perf test suite on this PR at a4224d6. You can monitor the build here.

Update: The results are in!

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

Here they are:

Comparison Report - main..45711

Metric	main	45711	Delta	Best	Worst
Angular - node (v10.16.3, x64)
Memory used	351,498k (± 0.02%)	351,568k (± 0.02%)	+70k (+ 0.02%)	351,360k	351,643k
Parse Time	1.90s (± 0.34%)	1.91s (± 0.68%)	+0.01s (+ 0.63%)	1.89s	1.94s
Bind Time	0.85s (± 0.76%)	0.86s (± 0.69%)	+0.01s (+ 0.94%)	0.85s	0.87s
Check Time	5.40s (± 0.45%)	5.41s (± 0.37%)	+0.01s (+ 0.24%)	5.36s	5.47s
Emit Time	5.83s (± 0.29%)	5.86s (± 0.64%)	+0.03s (+ 0.55%)	5.77s	5.95s
Total Time	13.97s (± 0.26%)	14.04s (± 0.38%)	+0.07s (+ 0.48%)	13.88s	14.14s
Compiler-Unions - node (v10.16.3, x64)
Memory used	203,519k (± 0.04%)	203,445k (± 0.03%)	-74k (- 0.04%)	203,329k	203,611k
Parse Time	0.78s (± 0.85%)	0.79s (± 0.89%)	+0.01s (+ 1.15%)	0.77s	0.80s
Bind Time	0.52s (± 1.43%)	0.52s (± 1.66%)	-0.00s (- 0.19%)	0.51s	0.54s
Check Time	7.84s (± 0.50%)	7.89s (± 0.64%)	+0.05s (+ 0.66%)	7.76s	7.99s
Emit Time	2.44s (± 0.70%)	2.46s (± 0.74%)	+0.02s (+ 0.61%)	2.42s	2.49s
Total Time	11.58s (± 0.37%)	11.65s (± 0.54%)	+0.07s (+ 0.60%)	11.51s	11.77s
Monaco - node (v10.16.3, x64)
Memory used	340,627k (± 0.03%)	340,619k (± 0.02%)	-9k (- 0.00%)	340,464k	340,827k
Parse Time	1.45s (± 0.90%)	1.46s (± 0.46%)	+0.01s (+ 0.76%)	1.44s	1.47s
Bind Time	0.75s (± 1.07%)	0.75s (± 0.60%)	0.00s ( 0.00%)	0.74s	0.76s
Check Time	5.44s (± 0.60%)	5.41s (± 0.72%)	-0.03s (- 0.50%)	5.31s	5.49s
Emit Time	3.16s (± 0.86%)	3.16s (± 1.04%)	+0.01s (+ 0.25%)	3.11s	3.26s
Total Time	10.79s (± 0.44%)	10.78s (± 0.29%)	-0.01s (- 0.05%)	10.71s	10.86s
TFS - node (v10.16.3, x64)
Memory used	303,979k (± 0.03%)	304,033k (± 0.02%)	+55k (+ 0.02%)	303,923k	304,196k
Parse Time	1.18s (± 0.59%)	1.18s (± 0.31%)	+0.00s (+ 0.25%)	1.18s	1.19s
Bind Time	0.71s (± 0.52%)	0.71s (± 0.69%)	-0.00s (- 0.14%)	0.71s	0.73s
Check Time	4.92s (± 0.65%)	4.93s (± 0.43%)	+0.01s (+ 0.20%)	4.89s	4.97s
Emit Time	3.32s (± 1.36%)	3.32s (± 1.45%)	+0.00s (+ 0.06%)	3.22s	3.43s
Total Time	10.13s (± 0.60%)	10.15s (± 0.56%)	+0.01s (+ 0.13%)	10.00s	10.28s
material-ui - node (v10.16.3, x64)
Memory used	469,920k (± 0.02%)	469,714k (± 0.01%)	-207k (- 0.04%)	469,641k	469,788k
Parse Time	1.73s (± 0.70%)	1.74s (± 0.61%)	+0.01s (+ 0.35%)	1.72s	1.76s
Bind Time	0.66s (± 0.45%)	0.67s (± 0.67%)	+0.01s (+ 0.91%)	0.66s	0.68s
Check Time	14.19s (± 0.63%)	14.44s (± 0.92%)	+0.25s (+ 1.76%)	14.17s	14.71s
Emit Time	0.00s (± 0.00%)	0.00s (± 0.00%)	0.00s ( NaN%)	0.00s	0.00s
Total Time	16.59s (± 0.55%)	16.85s (± 0.85%)	+0.26s (+ 1.56%)	16.57s	17.15s
Angular - node (v12.1.0, x64)
Memory used	329,562k (± 0.02%)	329,438k (± 0.08%)	-124k (- 0.04%)	328,468k	329,679k
Parse Time	1.89s (± 0.82%)	1.89s (± 0.77%)	+0.00s (+ 0.05%)	1.86s	1.92s
Bind Time	0.84s (± 0.95%)	0.84s (± 0.79%)	+0.00s (+ 0.12%)	0.83s	0.86s
Check Time	5.25s (± 0.64%)	5.28s (± 0.93%)	+0.03s (+ 0.50%)	5.14s	5.34s
Emit Time	6.08s (± 0.55%)	6.11s (± 0.53%)	+0.03s (+ 0.54%)	6.02s	6.17s
Total Time	14.06s (± 0.43%)	14.12s (± 0.57%)	+0.06s (+ 0.43%)	13.92s	14.24s
Compiler-Unions - node (v12.1.0, x64)
Memory used	190,701k (± 0.32%)	190,839k (± 0.13%)	+137k (+ 0.07%)	190,261k	191,234k
Parse Time	0.78s (± 0.77%)	0.78s (± 0.85%)	+0.00s (+ 0.52%)	0.77s	0.80s
Bind Time	0.54s (± 0.92%)	0.53s (± 0.84%)	-0.00s (- 0.75%)	0.53s	0.55s
Check Time	7.41s (± 0.69%)	7.42s (± 0.79%)	+0.01s (+ 0.18%)	7.26s	7.54s
Emit Time	2.46s (± 1.08%)	2.47s (± 0.92%)	+0.01s (+ 0.61%)	2.43s	2.53s
Total Time	11.17s (± 0.46%)	11.20s (± 0.59%)	+0.03s (+ 0.26%)	11.02s	11.35s
Monaco - node (v12.1.0, x64)
Memory used	323,777k (± 0.02%)	323,810k (± 0.02%)	+33k (+ 0.01%)	323,637k	323,961k
Parse Time	1.43s (± 0.61%)	1.44s (± 0.77%)	+0.01s (+ 0.63%)	1.42s	1.46s
Bind Time	0.73s (± 0.50%)	0.73s (± 0.41%)	+0.01s (+ 0.83%)	0.73s	0.74s
Check Time	5.30s (± 0.34%)	5.32s (± 0.75%)	+0.02s (+ 0.38%)	5.23s	5.43s
Emit Time	3.19s (± 0.71%)	3.19s (± 0.63%)	-0.01s (- 0.22%)	3.15s	3.24s
Total Time	10.65s (± 0.16%)	10.68s (± 0.60%)	+0.02s (+ 0.23%)	10.52s	10.83s
TFS - node (v12.1.0, x64)
Memory used	288,768k (± 0.02%)	288,762k (± 0.02%)	-6k (- 0.00%)	288,621k	288,915k
Parse Time	1.21s (± 0.72%)	1.22s (± 0.83%)	+0.01s (+ 0.66%)	1.20s	1.24s
Bind Time	0.71s (± 1.36%)	0.70s (± 1.18%)	-0.00s (- 0.56%)	0.69s	0.72s
Check Time	4.87s (± 0.49%)	4.87s (± 0.29%)	+0.01s (+ 0.12%)	4.85s	4.90s
Emit Time	3.39s (± 1.13%)	3.38s (± 0.61%)	-0.01s (- 0.32%)	3.32s	3.42s
Total Time	10.17s (± 0.63%)	10.17s (± 0.25%)	+0.00s (+ 0.04%)	10.10s	10.23s
material-ui - node (v12.1.0, x64)
Memory used	448,584k (± 0.02%)	448,412k (± 0.06%)	-172k (- 0.04%)	447,378k	448,617k
Parse Time	1.72s (± 0.62%)	1.73s (± 0.64%)	+0.01s (+ 0.64%)	1.70s	1.75s
Bind Time	0.65s (± 0.90%)	0.65s (± 1.02%)	+0.01s (+ 0.93%)	0.63s	0.66s
Check Time	12.85s (± 0.43%)	13.00s (± 0.75%)	+0.15s (+ 1.14%)	12.79s	13.19s
Emit Time	0.00s (± 0.00%)	0.00s (± 0.00%)	0.00s ( NaN%)	0.00s	0.00s
Total Time	15.22s (± 0.32%)	15.38s (± 0.66%)	+0.16s (+ 1.08%)	15.15s	15.59s
Angular - node (v14.15.1, x64)
Memory used	328,088k (± 0.01%)	328,103k (± 0.01%)	+15k (+ 0.00%)	328,050k	328,149k
Parse Time	1.90s (± 0.73%)	1.91s (± 0.64%)	+0.01s (+ 0.63%)	1.89s	1.94s
Bind Time	0.88s (± 0.51%)	0.88s (± 0.93%)	+0.00s (+ 0.11%)	0.87s	0.91s
Check Time	5.30s (± 0.76%)	5.32s (± 0.67%)	+0.02s (+ 0.32%)	5.24s	5.43s
Emit Time	6.22s (± 0.72%)	6.18s (± 0.70%)	-0.04s (- 0.71%)	6.11s	6.31s
Total Time	14.30s (± 0.51%)	14.29s (± 0.54%)	-0.01s (- 0.09%)	14.18s	14.55s
Compiler-Unions - node (v14.15.1, x64)
Memory used	191,742k (± 0.55%)	192,190k (± 0.49%)	+448k (+ 0.23%)	189,614k	192,907k
Parse Time	0.81s (± 0.92%)	0.81s (± 0.45%)	-0.00s (- 0.12%)	0.80s	0.81s
Bind Time	0.56s (± 0.85%)	0.56s (± 0.99%)	+0.01s (+ 0.90%)	0.55s	0.58s
Check Time	7.55s (± 0.61%)	7.55s (± 0.52%)	-0.00s (- 0.03%)	7.49s	7.68s
Emit Time	2.48s (± 1.01%)	2.46s (± 0.82%)	-0.02s (- 0.73%)	2.41s	2.49s
Total Time	11.39s (± 0.32%)	11.37s (± 0.48%)	-0.02s (- 0.16%)	11.27s	11.54s
Monaco - node (v14.15.1, x64)
Memory used	322,540k (± 0.00%)	322,541k (± 0.00%)	+1k (+ 0.00%)	322,511k	322,563k
Parse Time	1.48s (± 0.68%)	1.49s (± 0.67%)	+0.00s (+ 0.20%)	1.47s	1.51s
Bind Time	0.76s (± 0.66%)	0.76s (± 0.99%)	+0.00s (+ 0.26%)	0.75s	0.78s
Check Time	5.23s (± 0.43%)	5.23s (± 0.51%)	+0.01s (+ 0.13%)	5.19s	5.29s
Emit Time	3.21s (± 0.69%)	3.24s (± 1.03%)	+0.02s (+ 0.72%)	3.18s	3.31s
Total Time	10.68s (± 0.34%)	10.72s (± 0.42%)	+0.03s (+ 0.32%)	10.63s	10.82s
TFS - node (v14.15.1, x64)
Memory used	287,700k (± 0.01%)	287,713k (± 0.01%)	+13k (+ 0.00%)	287,663k	287,761k
Parse Time	1.26s (± 2.81%)	1.26s (± 2.13%)	+0.00s (+ 0.24%)	1.21s	1.33s
Bind Time	0.73s (± 1.27%)	0.73s (± 1.11%)	+0.00s (+ 0.27%)	0.72s	0.75s
Check Time	4.87s (± 0.35%)	4.91s (± 0.46%)	+0.04s (+ 0.76%)	4.84s	4.97s
Emit Time	3.47s (± 0.77%)	3.49s (± 0.84%)	+0.02s (+ 0.72%)	3.43s	3.57s
Total Time	10.32s (± 0.42%)	10.38s (± 0.43%)	+0.07s (+ 0.65%)	10.27s	10.46s
material-ui - node (v14.15.1, x64)
Memory used	447,030k (± 0.01%)	446,950k (± 0.00%)	-80k (- 0.02%)	446,922k	446,990k
Parse Time	1.76s (± 0.48%)	1.77s (± 0.33%)	+0.01s (+ 0.63%)	1.76s	1.78s
Bind Time	0.69s (± 0.58%)	0.69s (± 0.49%)	+0.00s (+ 0.29%)	0.69s	0.70s
Check Time	13.02s (± 0.60%)	13.13s (± 0.71%)	+0.12s (+ 0.88%)	12.87s	13.26s
Emit Time	0.00s (± 0.00%)	0.00s (± 0.00%)	0.00s ( NaN%)	0.00s	0.00s
Total Time	15.47s (± 0.50%)	15.59s (± 0.59%)	+0.13s (+ 0.83%)	15.33s	15.72s

System

Machine Name	ts-ci-ubuntu
Platform	linux 4.4.0-210-generic
Architecture	x64
Available Memory	16 GB
Available Memory	9 GB
CPUs	4 × 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	45711	10
Baseline	main	10

Developer Information:

Download Benchmark

Changed the tail recursion logic to bypass caching since it is effectively just computing temporary results. There's still a slight slowdown in material-ui (<1%), but generally I think not caching in the tail recursion loop is the best approach.

@ahejlsberg Thanks for this work! Using 4.4.3, I just hit the instantiationDepth === 50 limit (literally just 50, nothing above that) on a project I am working on.

Because it is possible / even likely to hit this depth limit of 50 with tuple types and template literal types in 4.4, I'm wondering if it would be possible to backport the instantiationDepth === 100 limit to a new release of 4.4 without including this tail recursive evaluation strategy This would mitigate the issue until 4.5 is released with this new (awesome) work. Let me know if you think this would be possible / a good idea. Thanks!