From c03ce23ea62a0e6e8295fdd82d58b20304ff1c6e Mon Sep 17 00:00:00 2001
From: A4-Tacks <wdsjxhno1001@163.com>
Date: Sat, 1 Nov 2025 16:22:37 +0800
Subject: [PATCH] Add ide-assist: unmerge_else_if

Unmerge `else if` into the `else {}`.

Example
---
```rust
fn foo() {
    if cond1 {
        xxx()
    } else if$0 cond2 {
        yyy()
    } else {
        zzz()
    }
}
```
->
```rust
fn foo() {
    if cond1 {
        xxx()
    } else {
        if cond2 {
            yyy()
        } else {
            zzz()
        }
    }
}
```
---
 .../src/handlers/unmerge_else_if.rs           | 135 ++++++++++++++++++
 crates/ide-assists/src/lib.rs                 |   2 +
 crates/ide-assists/src/tests/generated.rs     |  31 ++++
 3 files changed, 168 insertions(+)
 create mode 100644 crates/ide-assists/src/handlers/unmerge_else_if.rs

diff --git a/crates/ide-assists/src/handlers/unmerge_else_if.rs b/crates/ide-assists/src/handlers/unmerge_else_if.rs
new file mode 100644
index 000000000000..16f65849f684
--- /dev/null
+++ b/crates/ide-assists/src/handlers/unmerge_else_if.rs
@@ -0,0 +1,135 @@
+use crate::{
+    AssistId,
+    assist_context::{AssistContext, Assists},
+};
+use syntax::{
+    AstNode, T,
+    ast::{self, edit::AstNodeEdit, syntax_factory::SyntaxFactory},
+};
+
+// Assist: unmerge_else_if
+//
+// Unmerge `else if` into the `else {}`.
+//
+// ```
+// fn foo() {
+//     if cond1 {
+//         xxx()
+//     } else if$0 cond2 {
+//         yyy()
+//     } else {
+//         zzz()
+//     }
+// }
+// ```
+// ->
+// ```
+// fn foo() {
+//     if cond1 {
+//         xxx()
+//     } else {
+//         if cond2 {
+//             yyy()
+//         } else {
+//             zzz()
+//         }
+//     }
+// }
+// ```
+pub(crate) fn unmerge_else_if(acc: &mut Assists, ctx: &AssistContext<'_>) -> Option<()> {
+    let if_keyword = ctx.find_token_syntax_at_offset(T![if])?;
+    let if_expr = if_keyword.parent().and_then(ast::IfExpr::cast)?;
+    let _parent_if = if_expr.syntax().parent().and_then(ast::IfExpr::cast)?;
+
+    let target = if_expr.syntax().text_range();
+    acc.add(AssistId::refactor_rewrite("unmerge_else_if"), "Unmerge else if", target, |builder| {
+        let mut edit = builder.make_editor(if_expr.syntax());
+        let make = SyntaxFactory::with_mappings();
+
+        let new_if_expr = if_expr.reset_indent().indent(1.into()).into();
+        let new_block = make.block_expr(None, Some(new_if_expr)).indent(if_expr.indent_level());
+        edit.replace(if_expr.syntax(), new_block.syntax());
+
+        edit.add_mappings(make.finish_with_mappings());
+        builder.add_file_edits(ctx.vfs_file_id(), edit);
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_assist, check_assist_not_applicable};
+
+    use super::*;
+
+    #[test]
+    fn with_indent() {
+        check_assist(
+            unmerge_else_if,
+            r#"
+            fn foo() {
+                {
+                    if cond1 {
+                        xxx()
+                    } else if$0 cond2 {
+                        yyy(
+                            "..."
+                        )
+                    } else {
+                        zzz(
+                            "..."
+                        )
+                    }
+                }
+            }"#,
+            r#"
+            fn foo() {
+                {
+                    if cond1 {
+                        xxx()
+                    } else {
+                        if cond2 {
+                            yyy(
+                                "..."
+                            )
+                        } else {
+                            zzz(
+                                "..."
+                            )
+                        }
+                    }
+                }
+            }"#,
+        );
+    }
+
+    #[test]
+    fn not_applicable_outside_if_keyword() {
+        check_assist_not_applicable(
+            unmerge_else_if,
+            r#"
+            fn foo() {
+                if cond1 {
+                    xxx()
+                } else if cond2$0 {
+                    yyy()
+                } else {
+                    zzz()
+                }
+            }"#,
+        );
+
+        check_assist_not_applicable(
+            unmerge_else_if,
+            r#"
+            fn foo() {
+                if cond1 {
+                    xxx()
+                } else$0 if cond2 {
+                    yyy()
+                } else {
+                    zzz()
+                }
+            }"#,
+        );
+    }
+}
diff --git a/crates/ide-assists/src/lib.rs b/crates/ide-assists/src/lib.rs
index e9f2d686465e..a99836426327 100644
--- a/crates/ide-assists/src/lib.rs
+++ b/crates/ide-assists/src/lib.rs
@@ -225,6 +225,7 @@ mod handlers {
     mod toggle_async_sugar;
     mod toggle_ignore;
     mod toggle_macro_delimiter;
+    mod unmerge_else_if;
     mod unmerge_imports;
     mod unmerge_match_arm;
     mod unnecessary_async;
@@ -372,6 +373,7 @@ mod handlers {
             toggle_ignore::toggle_ignore,
             toggle_macro_delimiter::toggle_macro_delimiter,
             unmerge_match_arm::unmerge_match_arm,
+            unmerge_else_if::unmerge_else_if,
             unmerge_imports::unmerge_imports,
             unnecessary_async::unnecessary_async,
             unqualify_method_call::unqualify_method_call,
diff --git a/crates/ide-assists/src/tests/generated.rs b/crates/ide-assists/src/tests/generated.rs
index a99fe8de333d..5bd07a0e0cbc 100644
--- a/crates/ide-assists/src/tests/generated.rs
+++ b/crates/ide-assists/src/tests/generated.rs
@@ -3577,6 +3577,37 @@ sth!{ }
     )
 }
 
+#[test]
+fn doctest_unmerge_else_if() {
+    check_doc_test(
+        "unmerge_else_if",
+        r#####"
+fn foo() {
+    if cond1 {
+        xxx()
+    } else if$0 cond2 {
+        yyy()
+    } else {
+        zzz()
+    }
+}
+"#####,
+        r#####"
+fn foo() {
+    if cond1 {
+        xxx()
+    } else {
+        if cond2 {
+            yyy()
+        } else {
+            zzz()
+        }
+    }
+}
+"#####,
+    )
+}
+
 #[test]
 fn doctest_unmerge_imports() {
     check_doc_test(