imports_granularity = "Module" with path contains self (#4716)

* Fix for issue 4681 - Module imports_granularity and self in path

* Change wrong rustfmt-imports_granularity Item in test file to Module

Author: davidBar-On

Diff for: src/formatting/imports.rs

@@ -168,7 +168,19 @@ pub(crate) fn merge_use_trees(use_trees: Vec<UseTree>, merge_by: SharedPrefix) -
             continue;
         }
 
-        for flattened in use_tree.flatten() {
+        for mut flattened in use_tree.flatten() {
+            if merge_by == SharedPrefix::Module {
+                // If a path ends in `::self`, rewrite it to `::{self}`.
+                if let Some(UseSegment::Slf(..)) = flattened.path.last() {
+                    let self_segment = flattened.path.pop().unwrap();
+                    flattened
+                        .path
+                        .push(UseSegment::List(vec![UseTree::from_path(
+                            vec![self_segment],
+                            DUMMY_SP,
+                        )]));
+                }
+            }
             if let Some(tree) = result
                 .iter_mut()
                 .find(|tree| tree.share_prefix(&flattened, merge_by))

Diff for: tests/source/issue-4681-imports_granularity_default.rs

@@ -0,0 +1,6 @@
+use crate::lexer;
+use crate::lexer::tokens::TokenData;
+use crate::lexer::{tokens::TokenData};
+use crate::lexer::self;
+use crate::lexer::{self};
+use crate::lexer::{self, tokens::TokenData};

Diff for: tests/source/issue-4681-imports_granularity_module.rs

@@ -0,0 +1,5 @@
+// rustfmt-imports_granularity: Module
+
+use crate::lexer;
+use crate::lexer::self;
+use crate::lexer::{self, tokens::TokenData};

Diff for: tests/target/issue-4681-imports_granularity_default.rs

@@ -0,0 +1,6 @@
+use crate::lexer;
+use crate::lexer;
+use crate::lexer::tokens::TokenData;
+use crate::lexer::tokens::TokenData;
+use crate::lexer::{self};
+use crate::lexer::{self, tokens::TokenData};

Diff for: tests/target/issue-4681-imports_granularity_module.rs

@@ -0,0 +1,5 @@
+// rustfmt-imports_granularity: Module
+
+use crate::lexer;
+use crate::lexer::tokens::TokenData;
+use crate::lexer::{self};