Code change:
}; let last_type_ascription_set = self.last_type_ascription.is_some(); <del> match (self.expr_is_complete(&lhs), AssocOp::from_token(&self.token)) { (true, None) => { self.last_type_ascription = None; // Semi-statement forms are odd. See https://github.com/rust-lang/rust/issues/29071 return Ok(lhs); } (false, _) => {} // continue parsing the expression // An exhaustive check is done in the following block, but these are checked first // because they *are* ambiguous but also reasonable looking incorrect syntax, so we // want to keep their span info to improve diagnostics in these cases in a later stage. (true, Some(AssocOp::Multiply)) | // `{ 42 } *foo = bar;` or `{ 42 } * 3` (true, Some(AssocOp::Subtract)) | // `{ 42 } -5` (true, Some(AssocOp::LAnd)) | // `{ 42 } &&x` (#61475) (true, Some(AssocOp::Add)) // `{ 42 } + 42 // If the next token is a keyword, then the tokens above *are* unambiguously incorrect: // `if x { a } else { b } && if y { c } else { d }` if !self.look_ahead(1, |t| t.is_reserved_ident()) => { self.last_type_ascription = None; // These cases are ambiguous and can't be identified in the parser alone let sp = self.sess.source_map().start_point(self.token.span); self.sess.ambiguous_block_expr_parse.borrow_mut().insert(sp, lhs.span); return Ok(lhs); } (true, Some(ref op)) if !op.can_continue_expr_unambiguously() => { self.last_type_ascription = None; return Ok(lhs); } (true, Some(_)) => { // We've found an expression that would be parsed as a statement, but the next // token implies this should be parsed as an expression. // For example: `if let Some(x) = x { x } else { 0 } / 2` let mut err = self.struct_span_err(self.token.span, &format!( "expected expression, found `{}`", pprust::token_to_string(&self.token), )); err.span_label(self.token.span, "expected expression"); self.sess.expr_parentheses_needed( &mut err, lhs.span, Some(pprust::expr_to_string(&lhs), )); err.emit(); } </del> <ins> if !self.should_continue_as_assoc_expr(&lhs) { self.last_type_ascription = None; return Ok(lhs); </ins> } <del> self.expected_tokens.push(TokenType::Operator); while let Some(op) = AssocOp::from_token(&self.token) { </del> <ins> self.expected_tokens.push(TokenType::Operator); while let Some(op) = self.check_assoc_op() { </ins> // Adjust the span for interpolated LHS to point to the `$lhs` token and not to what // it refers to. Interpolated identifiers are unwrapped early and never show up here // as `PrevTokenKind::Interpolated` so if LHS is a single identifier we always process

Related discussion:
text: The idea of shortening to has been discussed many times before, and the general consensus always ends up being that it is not a good idea. I would like to propose something a bit different, so please hear me out. I propose that instead of aliasing to , we instead just make expand into when in the context of a variable declaration. For example: This solves the problems (readability, more concise) that people have with , whilst not causing the issues that people have (pattern matching and consistancy). The most common issue people have with aliasing to is that it doesn't fit well with patterns, like . However, gets rid of this problem, because you wouldn't write if you were trying to pattern match, so why would someone want to write ? You wouldn't do that, and it wouldn't compile. This would be optional, of course. would still work fine, and people would just have to option of removing the to let it be implied. There are a lot of other abbreviations used in rust (, , ) that all serve the purpose of writing less. It just doesn't feel right that one of the most commonly used keywords is so long. :heart::crab: <!-- TRIAGEBOTSTART --<!-- TRIAGEBOTASSIGNSTART --<!-- TRIAGEBOTASSIGNDATASTARTTRIAGEBOTASSIGNDATAEND --<!-- TRIAGEBOTASSIGNEND --<!-- TRIAGEBOTEND --
Rust wants to make to make you think when you try and use mutation, even if only a little bit, because mutation can be difficult to reason about. Shortening to doesn't fit this philosophy. Also, this makes mutation just as easy as no mutation. This will lead people to choose mutation because it will give them less compiler errors in the short term, and in doing so open themselves up to some weird bugs that could have been prevented with the syntactic salt that is . tldr: wasn't rejected because of the name , but because it allowed easy mutation, which runs counter to Rust's philosophy.
I politely disagree. In fact, it is actually the other way around. Using unnecessarily will cause compiler warnings, discouraging the use of unneeded mutability. The compiler doesn't warn when the use of is actually needed.
The fact that people will choose in the face of compiler warnings has been shown in practice, across many projects.