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Bug: Recursive generic union type synonyms cause poor compiler performance #10451
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- changed the title
[-]Bug: Recursive generic type synonyms cause poor compiler performance[/-][+]Bug: Recursive generic union type synonyms cause poor compiler performance[/+]on Aug 20, 2016 Hi,
this issue can still be reproduced with current master (9afb07d). On my machine, the example takes 8 seconds to compile, and if the fourth line is commented out, node crashes with "JavaScript heap out of memory".
looks like a duplicate of the same underlying issue in #10759.
Anonymous types are not cached when doing generic instantiations, causing a lot of these to happen than there should be. the work around is to use named types. e.g.:
interface A<T> { a: TSynonym<T> } interface B<T> { b: TSynonym<T> } interface C<T> { c: TSynonym<T> } interface D<T> { d: TSynonym<T> } type T<V> = A<V> | B<V> | C<V> | D<V>; type TSynonym<A> = T<A> function f<A>(): T<A> { return g<A>() } function g<A>(): T<A> { return h<A>() } function h<A>(): T<A> { }
This has been fixed by the type alias instantiation caching logic that was added in #12114. The OP example now type checks in effectively zero time.
Reacted by Benjamin Hodgson- locked and limited conversation to collaborators
on Jun 19, 2018
TypeScript Version: 1.8.10 and 2.1.0-dev.20160818
Code
Expected behavior:
Type error, in a reasonable length of time (because
gandhdo not return a value).Actual behavior:
This example takes over 7 seconds to (fail to) compile on my machine (a new, maxed-out MacBook Pro) and peaks at over 400MB of memory. Uncommenting the fourth line of
T's declaration causes the compiler to crash with an out-of-memory error after about a minute. Uncommenting the call tohdoubles the compilation time to 14 seconds and increases peak memory usage to over 1GB.Removing
TSynonym(so that the body ofTusesTdirectly), or removing all the generic types, improves the performance significantly.My guess is that the type-checker is recursively expanding the definitions of
TandTSynonymwhen it tries to type-check the functions, resulting in a very large quantity of nested union types.Here is the output of
tscwith the--diagnosticsflag: