FillConsoleOutputCharacterA crashes conhost when passed an invalid character

[j4james]

Environment

Windows build number: Version 10.0.18362.535

Steps to reproduce

Compile and run the following C program in a conhost shell:

#include <windows.h>

void main() {
    SetConsoleOutputCP(50220);
    HANDLE handle = GetStdHandle(STD_OUTPUT_HANDLE);
    DWORD written;
    FillConsoleOutputCharacterA(handle, 14, 1, COORD{ 0,0 }, &written); 
}

Expected behavior

I believe codepoint 14 is invalid in the given codepage, so I would expect it to write out something like the unicode replacement character in the top left corner of the screen buffer, or possibly nothing at all. The legacy console seems to write out a null character.

Actual behavior

The conhost crashes.

What's happening is that the FillConsoleOutputCharacterAImpl method is calling ConvertToW with a string that can't be converted in the given codepage. And ConvertToW then throws an exception when MultiByteToWideChar returns 0.

terminal/src/types/convert.cpp

Lines 41 to 42 in 9e5792b

	int const iTarget = MultiByteToWideChar(codePage, 0, source.data(), iSource, nullptr, 0);
	THROW_LAST_ERROR_IF(0 == iTarget);

And note that FillConsoleOutputCharacterAImpl is declared as noexcept, even though it quite clearly is capable of throwing exceptions. I've actually noticed a few cases like that - we may need to do an audit of our noexcept usage, and make sure it's being applied appropriately.

[mkitzan]

I'll PR a fix to this issue by wrapping the throwing call in a try-catch and making sure the output parameter cellsModified is set to 0 (which is what other FillConsoleOutputCharacter* do).

I'm down to do a noexcept audit, but it'll tie me up for bit. @DHowett-MSFT, let me know if it'd be more helpful to improve the settings warnings (#4299, #4239, #2440) for the time being instead (re:Email).

[ghost]

🎉This issue was addressed in #4309, which has now been successfully released as Windows Terminal Preview v0.9.433.0.:tada:

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