Add a WebAssembly version of System.Console.

[vargaz]

No description provided.

[vargaz]

This has about half the size (linked) as the normal unix version (21k vs 45k).

[stephentoub]

This has about half the size (linked) as the normal unix version (21k vs 45k).

What accounts for the difference?

[vargaz]

All the not implemented methods plus the simplified error handling, i.e. Interop.GetExceptionForIoErrno () is not used.

[stephentoub]

All the not implemented methods

What keeps them linked in? Presumably the app isn't calling them.

[vargaz]

There is a huge amount of code which reads the terminal database. Some virtual methods like the Read() methods are also retained.

[stephentoub]

There is a huge amount of code which reads the terminal database. Some virtual methods like the Read() methods are also retained.

Ok, thanks. I'm fine with this being merged, though I think it'd be good in the future for us to try to factor things in such a way that the linker could get rid of more, e.g. the terminal database, if it's not needed. It shouldn't be needed if the only thing the app is using is Console.ReadLine, for example. And it'd be nice if the size gains could accrue in the future to apps on other Unixes as well.

cc: @eerhardt

[ghost]

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[eerhardt]

though I think it'd be good in the future for us to try to factor things in such a way that the linker could get rid of more

My understanding is the issue is the virtual-ness of Stream. Since ConsoleStream derives from Stream, and the linker needs to preserve the base Stream.Read (for obvious reasons), I don't think it will trim ConsoleStream.Read. It would probably be pretty hard to figure out statically if a ConsoleStream is ever passed into a method that takes a Stream and calls .Read on it.

cc @vitek-karas @MichalStrehovsky @sbomer

[vargaz]

The terminal db code is being kept alive by:
ConsolePal:Write() -> UpdatedCachedCursorPosition() -> GetWindowSize() -> TerminalFormatStrings.Instance.

[stephentoub]

My understanding is the issue is the virtual-ness of Stream.

Isn't that Read small potatoes compared to the terminal db?

[eerhardt]

Isn't that Read small potatoes compared to the terminal db?

My point wasn't specifically Read, it was that the virtual methods on a derived Stream aren't able to be trimmed.

[stephentoub]

My point wasn't specifically Read, it was that the virtual methods on a derived Stream aren't able to be trimmed.

Understood, thanks. I'm highlighting that most of those overrides throw just like the one in this PR, they just throw a more appropriate exception that requires a tiny bit more logic to compute. So it doesn't look like we're saving a ton by having a custom ConsoleStream just for wasm; correct me if I'm wrong. The larger piece here seems to be the avoidance of the terminal db code, which ended up getting brought in per #35555 (comment) as part of 2ef9d36