Give integer literals a sign instead of relying on negation expressions

[oli-obk]

Proposal

Signed negative literals (e.g. -12) currently are represented as an unary negation expression with a positive literal inside. I want to change this to have literals (signed int, unsuffixed int, and floats) to contain a flag that states whether there's a negative sign.

From HIR onwards this is implemented in rust-lang/rust#136860 which shows that while moderately invasive, not as invasive as I feared.

Doing the same in the AST will require more care, as macro_rules macros can detect lit fragments, which today do not include negated literals.

The repeated usage of checking for a negated expression of a literal is imo an anti-pattern that we should avoid by accepting this MCP.

Mentors or Reviewers

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Process

The main points of the Major Change Process are as follows:

• File an issue describing the proposal.
• A compiler team member or contributor who is knowledgeable in the area can second by writing @rustbot second.
  • Finding a "second" suffices for internal changes. If however, you are proposing a new public-facing feature, such as a -C flag, then full team check-off is required.
  • Compiler team members can initiate a check-off via @rfcbot fcp merge on either the MCP or the PR.
• Once an MCP is seconded, the Final Comment Period begins. If no objections are raised after 10 days, the MCP is considered approved.

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Comments

This issue is not meant to be used for technical discussion. There is a Zulip stream for that. Use this issue to leave procedural comments, such as volunteering to review, indicating that you second the proposal (or third, etc), or raising a concern that you would like to be addressed.

[rustbot]

This issue is not meant to be used for technical discussion. There is a Zulip stream for that. Use this issue to leave procedural comments, such as volunteering to review, indicating that you second the proposal (or third, etc), or raising a concern that you would like to be addressed.

Concerns or objections to the proposal should be discussed on Zulip and formally registered here by adding a comment with the following syntax:

@rfcbot concern reason-for-concern 
<description of the concern> 

Concerns can be lifted with:

@rfcbot resolve reason-for-concern 

See documentation at https://forge.rust-lang.org

cc @rust-lang/compiler

[Urgau]

@rustbot second

[oli-obk]

While the 2 week period is over, let's hold up on merging this as accepted until folk had time to review the impl and finish the discussion on zulip