Add ide-assist: convert_range_for_to_while

Convert for each range into while loop.

```rust
fn foo() {
    $0for i in 3..7 {
        foo(i);
    }
}
```
->
```rust
fn foo() {
    let mut i = 3;
    while i < 7 {
        foo(i);
        i += 1;
    }
}
```

Author: A4-Tacks

src/tools/rust-analyzer/crates/ide-assists/src/handlers/convert_range_for_to_while.rs

@@ -0,0 +1,254 @@
+use ide_db::assists::AssistId;
+use itertools::Itertools;
+use syntax::{
+    AstNode, T,
+    algo::previous_non_trivia_token,
+    ast::{
+        self, HasArgList, HasLoopBody, HasName, RangeItem, edit::AstNodeEdit, make,
+        syntax_factory::SyntaxFactory,
+    },
+    syntax_editor::{Element, Position},
+};
+
+use crate::assist_context::{AssistContext, Assists};
+
+// Assist: convert_range_for_to_while
+//
+// Convert for each range into while loop.
+//
+// ```
+// fn foo() {
+//     $0for i in 3..7 {
+//         foo(i);
+//     }
+// }
+// ```
+// ->
+// ```
+// fn foo() {
+//     let mut i = 3;
+//     while i < 7 {
+//         foo(i);
+//         i += 1;
+//     }
+// }
+// ```
+pub(crate) fn convert_range_for_to_while(acc: &mut Assists, ctx: &AssistContext<'_>) -> Option<()> {
+    let for_kw = ctx.find_token_syntax_at_offset(T![for])?;
+    let for_ = ast::ForExpr::cast(for_kw.parent()?)?;
+    let ast::Pat::IdentPat(pat) = for_.pat()? else { return None };
+    let iterable = for_.iterable()?;
+    let (start, end, step, inclusive) = extract_range(&iterable)?;
+    let name = pat.name()?;
+    let body = for_.loop_body()?;
+    let last = previous_non_trivia_token(body.stmt_list()?.r_curly_token()?)?;
+
+    acc.add(
+        AssistId::refactor("convert_range_for_to_while"),
+        "Replace to while or loop",
+        for_.syntax().text_range(),
+        |builder| {
+            let mut edit = builder.make_editor(for_.syntax());
+            let make = SyntaxFactory::with_mappings();
+
+            let indent = for_.indent_level();
+            let pat = make.ident_pat(pat.ref_token().is_some(), true, name.clone());
+            let let_stmt = make.let_stmt(pat.into(), None, Some(start));
+            edit.insert_all(
+                Position::before(for_.syntax()),
+                vec![
+                    let_stmt.syntax().syntax_element(),
+                    make.whitespace(&format!("\n{}", indent)).syntax_element(),
+                ],
+            );
+
+            let mut elements = vec![];
+
+            let var_expr = make.expr_path(make.ident_path(&name.text()));
+            let op = ast::BinaryOp::CmpOp(ast::CmpOp::Ord {
+                ordering: ast::Ordering::Less,
+                strict: !inclusive,
+            });
+            if let Some(end) = end {
+                elements.extend([
+                    make.token(T![while]).syntax_element(),
+                    make.whitespace(" ").syntax_element(),
+                    make.expr_bin(var_expr.clone(), op, end).syntax().syntax_element(),
+                ]);
+            } else {
+                elements.push(make.token(T![loop]).syntax_element());
+            }
+
+            edit.replace_all(
+                for_kw.syntax_element()..=iterable.syntax().syntax_element(),
+                elements,
+            );
+
+            let op = ast::BinaryOp::Assignment { op: Some(ast::ArithOp::Add) };
+            edit.insert_all(
+                Position::after(last),
+                vec![
+                    make.whitespace(&format!("\n{}", indent + 1)).syntax_element(),
+                    make.expr_bin(var_expr, op, step).syntax().syntax_element(),
+                    make.token(T![;]).syntax_element(),
+                ],
+            );
+
+            edit.add_mappings(make.finish_with_mappings());
+            builder.add_file_edits(ctx.vfs_file_id(), edit);
+        },
+    )
+}
+
+fn extract_range(iterable: &ast::Expr) -> Option<(ast::Expr, Option<ast::Expr>, ast::Expr, bool)> {
+    Some(match iterable {
+        ast::Expr::ParenExpr(expr) => extract_range(&expr.expr()?)?,
+        ast::Expr::RangeExpr(range) => {
+            let inclusive = range.op_kind()? == ast::RangeOp::Inclusive;
+            (range.start()?, range.end(), make::expr_literal("1").into(), inclusive)
+        }
+        ast::Expr::MethodCallExpr(call) if call.name_ref()?.text() == "step_by" => {
+            let [step] = call.arg_list()?.args().collect_array()?;
+            let (start, end, _, inclusive) = extract_range(&call.receiver()?)?;
+            (start, end, step, inclusive)
+        }
+        _ => return None,
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_assist, check_assist_not_applicable};
+
+    use super::*;
+
+    #[test]
+    fn test_convert_range_for_to_while() {
+        check_assist(
+            convert_range_for_to_while,
+            "
+fn foo() {
+    $0for i in 3..7 {
+        foo(i);
+    }
+}
+            ",
+            "
+fn foo() {
+    let mut i = 3;
+    while i < 7 {
+        foo(i);
+        i += 1;
+    }
+}
+            ",
+        );
+    }
+
+    #[test]
+    fn test_convert_range_for_to_while_no_end_bound() {
+        check_assist(
+            convert_range_for_to_while,
+            "
+fn foo() {
+    $0for i in 3.. {
+        foo(i);
+    }
+}
+            ",
+            "
+fn foo() {
+    let mut i = 3;
+    loop {
+        foo(i);
+        i += 1;
+    }
+}
+            ",
+        );
+    }
+
+    #[test]
+    fn test_convert_range_for_to_while_with_mut_binding() {
+        check_assist(
+            convert_range_for_to_while,
+            "
+fn foo() {
+    $0for mut i in 3..7 {
+        foo(i);
+    }
+}
+            ",
+            "
+fn foo() {
+    let mut i = 3;
+    while i < 7 {
+        foo(i);
+        i += 1;
+    }
+}
+            ",
+        );
+    }
+
+    #[test]
+    fn test_convert_range_for_to_while_with_label() {
+        check_assist(
+            convert_range_for_to_while,
+            "
+fn foo() {
+    'a: $0for mut i in 3..7 {
+        foo(i);
+    }
+}
+            ",
+            "
+fn foo() {
+    let mut i = 3;
+    'a: while i < 7 {
+        foo(i);
+        i += 1;
+    }
+}
+            ",
+        );
+    }
+
+    #[test]
+    fn test_convert_range_for_to_while_step_by() {
+        check_assist(
+            convert_range_for_to_while,
+            "
+fn foo() {
+    $0for mut i in (3..7).step_by(2) {
+        foo(i);
+    }
+}
+            ",
+            "
+fn foo() {
+    let mut i = 3;
+    while i < 7 {
+        foo(i);
+        i += 2;
+    }
+}
+            ",
+        );
+    }
+
+    #[test]
+    fn test_convert_range_for_to_while_not_applicable_non_range() {
+        check_assist_not_applicable(
+            convert_range_for_to_while,
+            "
+fn foo() {
+    let ident = 3..7;
+    $0for mut i in ident {
+        foo(i);
+    }
+}
+            ",
+        );
+    }
+}

src/tools/rust-analyzer/crates/ide-assists/src/lib.rs

@@ -131,6 +131,7 @@ mod handlers {
     mod convert_match_to_let_else;
     mod convert_named_struct_to_tuple_struct;
     mod convert_nested_function_to_closure;
+    mod convert_range_for_to_while;
     mod convert_to_guarded_return;
     mod convert_tuple_return_type_to_struct;
     mod convert_tuple_struct_to_named_struct;
@@ -268,6 +269,7 @@ mod handlers {
             convert_match_to_let_else::convert_match_to_let_else,
             convert_named_struct_to_tuple_struct::convert_named_struct_to_tuple_struct,
             convert_nested_function_to_closure::convert_nested_function_to_closure,
+            convert_range_for_to_while::convert_range_for_to_while,
             convert_to_guarded_return::convert_to_guarded_return,
             convert_tuple_return_type_to_struct::convert_tuple_return_type_to_struct,
             convert_tuple_struct_to_named_struct::convert_tuple_struct_to_named_struct,

src/tools/rust-analyzer/crates/ide-assists/src/tests/generated.rs

@@ -731,6 +731,29 @@ fn main() {
     )
 }
 
+#[test]
+fn doctest_convert_range_for_to_while() {
+    check_doc_test(
+        "convert_range_for_to_while",
+        r#####"
+fn foo() {
+    $0for i in 3..7 {
+        foo(i);
+    }
+}
+"#####,
+        r#####"
+fn foo() {
+    let mut i = 3;
+    while i < 7 {
+        foo(i);
+        i += 1;
+    }
+}
+"#####,
+    )
+}
+
 #[test]
 fn doctest_convert_to_guarded_return() {
     check_doc_test(

src/tools/rust-analyzer/crates/syntax/src/ast/make.rs

@@ -1355,7 +1355,7 @@ pub mod tokens {
 
     pub(super) static SOURCE_FILE: LazyLock<Parse<SourceFile>> = LazyLock::new(|| {
         SourceFile::parse(
-            "use crate::foo; const C: <()>::Item = ( true && true , true || true , 1 != 1, 2 == 2, 3 < 3, 4 <= 4, 5 > 5, 6 >= 6, !true, *p, &p , &mut p, async { let _ @ [] })\n;\n\nunsafe impl A for B where: {}",
+            "use crate::foo; const C: <()>::Item = ( true && true , true || true , 1 != 1, 2 == 2, 3 < 3, 4 <= 4, 5 > 5, 6 >= 6, !true, *p, &p , &mut p, async { let _ @ [] }, while loop {} {})\n;\n\nunsafe impl A for B where: {}",
             Edition::CURRENT,
         )
     });

src/tools/rust-analyzer/crates/syntax/src/ast/syntax_factory/constructors.rs

@@ -644,6 +644,20 @@ impl SyntaxFactory {
         ast
     }
 
+    pub fn expr_loop(&self, body: ast::BlockExpr) -> ast::LoopExpr {
+        let ast::Expr::LoopExpr(ast) = make::expr_loop(body.clone()).clone_for_update() else {
+            unreachable!()
+        };
+
+        if let Some(mut mapping) = self.mappings() {
+            let mut builder = SyntaxMappingBuilder::new(ast.syntax().clone());
+            builder.map_node(body.syntax().clone(), ast.loop_body().unwrap().syntax().clone());
+            builder.finish(&mut mapping);
+        }
+
+        ast
+    }
+
     pub fn expr_while_loop(&self, condition: ast::Expr, body: ast::BlockExpr) -> ast::WhileExpr {
         let ast = make::expr_while_loop(condition.clone(), body.clone()).clone_for_update();