imports_granularity = "Module" with path contains self

[davidBar-On]

Suggested fix for #4681: when imports_granularity = "Module", the formatting output of use crate::lexer::{self, tokens::TokenData} includes now crate::lexer::{self} instead of crate::lexer::self.

The change in merge_use_trees() is based on the code in flatten_use_trees() that handles similar issue.

[calebcartwright]

This is wrong, although it kinda turned out well that you did this as it highlights a lack of dedupe we have with the Item variant (something separate)

Suggested change

	// rustfmt-imports_granularity: Item
	// rustfmt-imports_granularity: Module

[davidBar-On]

Oops! Fixed. (Probably was a last minute change as I did most of the tests by setting the configuration in the .toml file)

Note the test file changes, as with Module duplicates are removed in the formatted output, so made sure the related output is from the use crate::lexer::{self, tokens::TokenData} source line.

[calebcartwright]

Thanks! Will go ahead and merge so we can get the issue fixed, but if you're interested in take a follow up look I think it might be worthwhile to see if there's pieces that can be leveraged between the Module and Crate variant, since the latter obviously doesn't need this post correction

[calebcartwright]

Any ideas why this isn't needed for the Crate variant?

[davidBar-On]

As I understand, the following code transforms ahead foo::self to foo:

rustfmt/src/formatting/imports.rs

Lines 474 to 477 in 0e90855

	// Normalise foo::self -> foo.
	if let UseSegment::Slf(None) = last {
	if !self.path.is_empty() {
	return self;

Therefore, the only reason foo::self can be present in the code you asked about, is that flatten() created foo::self from foo::{self, bar}, in addition to creating foo::bar. For SharedPrefix::Module these too imports will remain separate, so {} should be added to self. However for SharedPrefix::Crate they will be merged again. This is because how share_prefix() identify shared prefix:

rustfmt/src/formatting/imports.rs

Lines 570 to 573 in 0e90855

	match shared_prefix {
	SharedPrefix::Crate => self.path[0] == other.path[0],
	SharedPrefix::Module => {
	self.path[..self.path.len() - 1] == other.path[..other.path.len() - 1]

When checking this I found two examples of imports formatting which I am not sure are correct. The first is when using imports_granularity = "Crate":

use foo;
use foo::{self};

is formatted as:

use foo::{
    self, {self},
};

Is that o.k. or it should have been use foo::{self}?

The second possible formatting issue is when using imports_granularity = "Module":

use foo;
use bar;

is formatted as:

use {bar, foo};

Is this o.k.?