Add SEMICOLON_IN_EXPRESSIONS_FROM_MACROS lint

[Aaron1011]

cc #79813

This PR adds an allow-by-default future-compatibility lint
SEMICOLON_IN_EXPRESSIONS_FROM_MACROS. It fires when a trailing semicolon in a
macro body is ignored due to the macro being used in expression
position:

macro_rules! foo {
    () => {
        true; // WARN
    }
}

fn main() {
    let val = match true {
        true => false,
        _ => foo!()
    };
}

The lint takes its level from the macro call site, and
can be allowed for a particular macro by adding
#[allow(macro_trailing_semicolon)].

The lint is set to warn for all internal rustc crates (when being built
by a stage1 compiler). After the next beta bump, we can enable
the lint for the bootstrap compiler as well.

[rust-highfive]

r? @matthewjasper

(rust-highfive has picked a reviewer for you, use r? to override)

[Aaron1011]

This becomes tricky when the macro is defined in a different crate. I think we need to instead take the lint level from the macro call site - otherwise, the warning becomes unsurpressable in downstream code.

[Aaron1011]

Unfortunately, inert attributes on macro invocations (e.g. #[allow(macro_trailing_semicolon)] my_macro!()) is an issue of its own: #63221

[Aaron1011]

Additionally, linting is currently done after HIR lowering, so the macro call doesn't even exist by the time we would be ready to emit the lint.

Implementing this will require some further thought.

[petrochenkov]

r? @petrochenkov

[petrochenkov]

I agree that the NodeId for linting should be taken from the use site rather than from definition site.

We have a method fn lint_node_id to obtain an ID that is close enough to the given macro invocation.
(#[allow(macro_trailing_semicolon)] my_macro!() still won't work though.)

[Dylan-DPC-zz]

@bors try

[bors]

⌛ Trying commit 1d8d56e95636056cf085c02decd7a386264310d3 with merge 50473808b4098f3d96d962b3940d38962305e408...

[Aaron1011]

@petrochenkov I've updated the PR to use lint_node_id

[petrochenkov]

The comment on macro_rules! declare_lint explains how to fix and test the lint-docs check.

[Aaron1011]

@bors r=petrochenkov

[bors]

📌 Commit f902551 has been approved by petrochenkov