Adds the result_and_inner_method lint (suspicious, warn-by-default).

[Souradip121]

Closes #16847

What the lint catches

Calling .and() on a Result<T, E> when the inner type T has an inherent method also named and. This is a footgun: Result::and discards the first Ok value entirely, which is rarely the intent when the inner type has its own and method.

// Before
fn foot_gun() -> Result<AndType, ()> {
    foo(0b0001).and(foo(0b1111))  // calls Result::and, discards first Ok value
}

// After (suggestion)
fn foot_gun() -> Result<AndType, ()> {
    Result::and(foo(0b0001), foo(0b1111))  // explicit: clearly calling Result::and
}

Conservative conditions (no false positives)

The lint is skipped when:

• The receiver is not Result<T, E>
• The inner type T has no inherent method named and (e.g. Result<u8, E> does not lint)
• The call is already in fully-qualified form (Result::and(a, b))

Only inherent methods are checked, not trait methods, which keeps the scope tight and avoids surprising users who implement custom traits with an and method on an unrelated type.

changelog: [result_and_inner_method]: new lint that warns when Result::and is called and the inner Ok type has an inherent and method, suggesting fully-qualified syntax to make the intent explicit.

[rustbot]

r? @samueltardieu

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The reviewer was selected based on:

• Owners of files modified in this PR: 7 candidates
• 7 candidates expanded to 7 candidates
• Random selection from Jarcho, dswij, llogiq, samueltardieu

[samueltardieu]

r? clippy

[ada4a]

sorry, don't have the capacity right now

r? clippy