Add ide-assist: merge_nested_else_if

crates/ide-assists/src/handlers/merge_nested_if.rs

@@ -1,7 +1,7 @@
 use ide_db::syntax_helpers::node_ext::is_pattern_cond;
 use syntax::{
     T,
-    ast::{self, AstNode, BinaryOp},
+    ast::{self, AstNode, BinaryOp, edit::AstNodeEdit},
 };
 
 use crate::{
@@ -89,6 +89,58 @@ pub(crate) fn merge_nested_if(acc: &mut Assists, ctx: &AssistContext<'_>) -> Opt
     })
 }
 
+// Assist: merge_nested_else_if
+//
+// This transforms `if x {} else { if y {} }` into `if x {} else if y {}`,
+// This assist can only be applied with the cursor on `else`.
+//
+// ```
+// fn main() {
+//     if x == 3 {
+//         true
+//     } $0else {
+//         if x == 2 {
+//             false
+//         } else {
+//             true
+//         }
+//     }
+// }
+// ```
+// ->
+// ```
+// fn main() {
+//     if x == 3 {
+//         true
+//     } else if x == 2 {
+//         false
+//     } else {
+//         true
+//     }
+// }
+// ```
+pub(crate) fn merge_nested_else_if(acc: &mut Assists, ctx: &AssistContext<'_>) -> Option<()> {
+    let else_keyword = ctx.find_token_syntax_at_offset(T![else])?;
+    let expr = ast::IfExpr::cast(else_keyword.parent()?)?;
+    let ast::ElseBranch::Block(else_block) = expr.else_branch()? else { return None };
+    let ast::Expr::IfExpr(else_expr) = else_block.tail_expr()? else { return None };
+
+    if else_block.statements().next().is_some() {
+        return None;
+    }
+
+    let target = else_keyword.text_range();
+    acc.add(
+        AssistId::refactor_rewrite("merge_nested_else_if"),
+        "Merge nested else if",
+        target,
+        |edit| {
+            let else_expr = else_expr.dedent(1.into()).into();
+            edit.replace_ast(ast::Expr::BlockExpr(else_block), else_expr);
+        },
+    )
+}
+
 /// Returns whether the given if condition has logical operators.
 fn has_logic_op_or(expr: &ast::Expr) -> bool {
     match expr {

crates/ide-assists/src/lib.rs

@@ -322,6 +322,7 @@ mod handlers {
             merge_imports::merge_imports,
             merge_match_arms::merge_match_arms,
             merge_nested_if::merge_nested_if,
+            merge_nested_if::merge_nested_else_if,
             move_bounds::move_bounds_to_where_clause,
             move_const_to_impl::move_const_to_impl,
             move_from_mod_rs::move_from_mod_rs,

crates/ide-assists/src/tests/generated.rs

@@ -2476,6 +2476,37 @@ fn handle(action: Action) {
     )
 }
 
+#[test]
+fn doctest_merge_nested_else_if() {
+    check_doc_test(
+        "merge_nested_else_if",
+        r#####"
+fn main() {
+    if x == 3 {
+        true
+    } $0else {
+        if x == 2 {
+            false
+        } else {
+            true
+        }
+    }
+}
+"#####,
+        r#####"
+fn main() {
+    if x == 3 {
+        true
+    } else if x == 2 {
+        false
+    } else {
+        true
+    }
+}
+"#####,
+    )
+}
+
 #[test]
 fn doctest_merge_nested_if() {
     check_doc_test(