Don't emit "is not a logical operator" error outside of associative expressions

[tgnottingham]

Avoid showing this error where it doesn't make sense by not assuming
"and" and "or" were intended to mean "&&" and "||" until after we decide
to continue parsing input as an associative expression.

Note that the decision of whether or not to continue parsing input as an
associative expression doesn't actually depend on this assumption.

Fixes #75599

---

First time contributor! Let me know if there are any conventions or policies I should be following that I missed here. Thanks :)

[rust-highfive]

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[tgnottingham]

r? @estebank

Hi @estebank, thought you might be the best person to review, since you've touched this part of the code recently.

---

Also, want to point out that, with this change, code like this...

fn foo(a: Option<u32>, b: Option<u32>) -> bool {
    if let Some(x) = a { true } else { false }
    and
    if let Some(y) = a { true } else { false }
}

...will no longer generate the suggestion to replace "and" with "&&". But it still suggests using parens to turn the construct into an expression, and after you do that, you will get the "and" -> "&&" suggestion.

Oops, I'm mistaken. It doesn't show the parens suggestion. But it does show the exact same errors as before, sans the "and" -> "&&" suggestion. Not sure if this is a deal-breaker.

error: expected one of `!`, `.`, `::`, `;`, `?`, `{`, `}`, or an operator, found keyword `if`
 --> src/main.rs:4:5
  |
3 |     and
  |        - expected one of 8 possible tokens
4 |     if let Some(y) = a { true } else { false }
  |     ^^ unexpected token

error[E0308]: mismatched types
 --> src/main.rs:2:26
  |
2 |     if let Some(x) = a { true } else { false }
  |     ---------------------^^^^------------------ help: consider using a semicolon here
  |     |                    |
  |     |                    expected `()`, found `bool`
  |     expected this to be `()`

error[E0308]: mismatched types
 --> src/main.rs:2:40
  |
2 |     if let Some(x) = a { true } else { false }
  |     -----------------------------------^^^^^--- help: consider using a semicolon here
  |     |                                  |
  |     |                                  expected `()`, found `bool`
  |     expected this to be `()`

[estebank]

This looks good to me. Can you squash the two commits? r=me after that.

[estebank]

But it does show the exact same errors as before, sans the "and" -> "&&" suggestion. Not sure if this is a deal-breaker.

That is unfortunate, but at the same time the code is far away from correct enough for us to accept the lack of helpful suggestions.

[tgnottingham]

Squashed the commits. Thanks @estebank.

[jyn514]

@bors r=estebank

[bors]

📌 Commit ff73a40 has been approved by estebank