Support if let guards in matches!() and assert_matches!() #152313

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1. theemathas

   added

   A-macrosArea: All kinds of macros (custom derive, macro_rules!, proc macros, ..)Area: All kinds of macros (custom derive, macro_rules!, proc macros, ..)

   T-libs-api[DEPRECATED; DO NOT USE][DEPRECATED; DO NOT USE]

   C-feature-requestCategory: A feature request, i.e: not implemented / a PR.Category: A feature request, i.e: not implemented / a PR.

   on Feb 8, 2026
2. rustbot

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   needs-triageThis issue may need triage. Remove when done. See docs forge.rust-lang.org/release/issue-triagingThis issue may need triage. Remove when done. See docs forge.rust-lang.org/release/issue-triaging

   on Feb 8, 2026
3. theemathas

   added

   A-patternsRelating to patterns and pattern matchingRelating to patterns and pattern matching

   and removed

   needs-triageThis issue may need triage. Remove when done. See docs forge.rust-lang.org/release/issue-triagingThis issue may need triage. Remove when done. See docs forge.rust-lang.org/release/issue-triaging

   on Feb 8, 2026
4. Kivooeo commented on Feb 12, 2026

   

   Kivooeo

   on Feb 12, 2026

   Member

   More actions

   In my opinion, it shouldn't. At least I couldn't come up with any useful examples. I thought about it when I was writing a blog post about 'if let' guards
5. theemathas commented on Feb 12, 2026

   

   theemathas

   on Feb 12, 2026

   ContributorAuthor

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   @Kivooeo Here's an artificial example of how it might be useful.

   struct Node {
       parent_id: Option<usize>,
   }
   
   fn has_great_grandparent(curr: &Node, nodes: &[Node]) -> bool {
       matches!(curr.parent_id, Some(p)
           if let Some(gp) = nodes[p].parent_id
           && nodes[gp].parent_id.is_some())
   }
6. theemathas commented on Feb 12, 2026

   

   theemathas

   on Feb 12, 2026

   ContributorAuthor

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   A more complicated example:

   enum Expr {
       Assign(String, usize),
       Sum(usize, usize),
       Var(String),
       Num(i32),
   }
   
   // check if an expression is the form "x = x + 1"
   fn is_increment(curr: &Expr, exprs: &[Expr]) -> bool {
       matches!(curr, Expr::Assign(lhs_name, rhs)
           if let Expr::Sum(operand1, operand2) = &exprs[rhs]
           && let Expr::Var(operand1_name) = &exprs[*operand1]
           && lhs_name == operand1_name
           && let Expr::Num(1) = exprs[*operand2]
       )
   }
7. theemathas commented on Feb 12, 2026

   

   theemathas

   on Feb 12, 2026

   ContributorAuthor

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   Real world code which could benefit from let-chains in assert_matches: https://github.com/rust-lang/rust/pull/152173/changes#diff-ee51fdc73fed0b3d6074a8e236e0482fc7e4893a11dd0f2b8823415ca5ebbd09R28

   👍React with 👍2Reacted by Asuna and Lu, Wangshan
8. JonathanBrouwer

   added 2 commits that reference this issue on Mar 25, 2026

   Rollup merge of rust-lang#153702 - SpriteOvO:guard-matcher, r=davidtwco

   ...

   5181637

   Rollup merge of rust-lang#153702 - SpriteOvO:guard-matcher, r=davidtwco

   ...

   6e3c174
9. flip1995

   added a commit that references this issue on Apr 4, 2026

   Rollup merge of rust-lang#153702 - SpriteOvO:guard-matcher, r=davidtwco

   ...

   ddfb974
10. rust-bors

    added a commit that references this issue on Jul 21, 2026

    Rollup merge of #153702 - SpriteOvO:guard-matcher, r=davidtwco

    ...

    6304720
11. clarfonthey

    added

    T-libsRelevant to the library team, which will review and decide on the PR/issue.Relevant to the library team, which will review and decide on the PR/issue.

    and removed

    T-libs-api[DEPRECATED; DO NOT USE][DEPRECATED; DO NOT USE]

    on Aug 12, 2026