redundant_pattern_matching added support for more complex patterns

[mendelsshop]

changelog: [redundant_pattern_matching]: Improved this lint by allowing to handle more complex patterns beyond just _

Before, the lint would only activate when the pattern was an _ or if the constructor was a unit constructor (like None):

while let Some(_) = Some(42) {}

But now it can also catch more complicated nested patterns

struct Foo { x: i32 }
enum E {
     Unit
}
if let Some((Foo { x: _}, _, E::Unit)) = None {}

The only thing it doesn't support right now is if the redundancy happens because of an or pattern.

if let Some(Some(Some(_) | None)) = None {}

Edit:
I also made that the only slice patterns that are checked are [..] and [] because in all the other cases we are constraining the size of what we are matching to be bigger:

if let Some([_, _, ..]) = Some(&[1] as &[i32]) {}

If we were to blindly apply the lint here we would get:

if Some(&[1] as &[i32]).is_some() {}

And the condition would (incorrectly) be true even if the slice was the less than length two.
For [T: N] we could make it work and only activate the lint if for the pattern [x0, ... xn] N > n.

fixes #16235

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[github-actions]

Lintcheck changes for 40a60e2

Lint	Added	Removed	Changed
clippy::redundant_pattern_matching_complex	11	0	0

This comment will be updated if you push new changes

[Jarcho]

Since this lint is enabled by default I'm going to use the same reasoning for let_unit_value and say we can't lint on this. People use the additional part of the pattern as an assertion about the types involved.

This also doesn't take into account if the pattern is needed for type inference. e.g.

fn foo<T>() -> Result<T, ()> {panic!()}
if let Ok(()) = foo() {}

[mendelsshop]

Ok, I see, would we want to turn the support for more complex patterns into a separate allow-by-default-lint?

[mendelsshop]

Ok so I added another lint for these more complex patterns, it uses the same logic as before, but if it finds a complex pattern it just emits a different lint.

I put it under nursery.