Add lint for inline assembly syntax style preference

[jethrogb]

changelog: Add lint for inline assembly syntax style preference

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @matthiaskrgr (or someone else) soon.

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[ebroto]

Thanks for your contribution and welcome to Clippy!

Currently Clippy is reluctant to accept new pre-expansion lints, as it's not clear if support for them will be removed at some point in rustc. Moreover, with a pre-expansion lint we would not be able to catch cases like the following:

#![feature(asm)]

macro_rules! nested {
    () => {
        asm!("");
    }
}

fn main() {
    unsafe {
        nested!();   
    }
}

Luckily, we don't need a pre-expansion pass. We can move the lints to an early pass, check for expressions whose kind is ExprKind::InlineAsm, and then check the syntax with

if inline_asm.options.contains(InlineAsmOptions::ATT_SYNTAX) {
   // ...
}

[ebroto]

r? @ebroto

[jethrogb]

Neat! That would've saved me a bunch of work 😃 Only downside is rustc_ast::ast::InlineAsm doesn't contain span information for the options.

[ebroto]

LGTM modulo the change I've added. If the tests pass I will merge it.

Thanks!

[ebroto]

@bors r+

[bors]

📌 Commit 507561e has been approved by ebroto

[bors]

⌛ Testing commit 507561e with merge abce9e7...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: ebroto
Pushing abce9e7 to master...