Mistyped standard attributes should give a warning

[cD1rtX3]

Type: Feature Request

I recently typed code similar to this:

switch (rule) {
    case EXPRESSION:
        /* ... */
        [[falthrough]];
    default:
}
/* ... */

Where's the error? It's hard to notice, but [[fallthrough]], a statement which tells the compiler not to warn on falling through the bottom of a case, is mistyped as [[falthrough]], without one of the Ls. Technically, this isn't a syntax error, but it should be a warning in VS Code since the statement won't do anything.

Extension version: 1.29.2
VS Code version: Code 1.106.3 (bf9252a2fb45be6893dd8870c0bf37e2e1766d61, 2025-11-25T22:28:18.024Z)
OS version: Linux x64 6.8.0-88-generic
Modes:

[cD1rtX3]

Yes, this is a feature in C.

[cD1rtX3]

This should also activate when you put a valid attribute like [[unsequenced]] in a spot it doesn't belong.

[sean-mcmanus]

@cD1rtX3 Does any compiler give a warning for that? How would we determine it's a misspelled attribute?

[cD1rtX3]

GCC throws “warning: ‘falthrough’ attribute ignored [-Wattributes]”. You can determine it's a misspelt attribute by noting that it isn't a correctly-spelt attribute.

[sean-mcmanus]

@cD1rtX3 Ah, okay, I see how -- our EDG parser also shows that warning, but the root issue is that we disable all warnings for IntelliSense and only show errors, so it's the same root issue as #828 , although we can keep this issue open for tracking the different warning case. You can modify the common.json to remove --no_warning to see warnings in general, but this particular cases also requires a binary change:

We'd probably want to investigate if anything could break by making that change. When I tried to enable the warnings back in 2018 there were complaints because VS doesn't expose those.

[sean-mcmanus]

@cD1rtX3 I've filed a feature request on VS at https://developercommunity.visualstudio.com/t/Show-C-IntelliSense-warnings-for-unrec/11013631 .