Merge #10257

10257: assists: turn while into loop r=Veykril a=agluszak

Implements an assist to turn a `while` loop into a `loop` loop, as requested in #10214. 
I'm not sure sure what the guidelines are regarding naming assists convert_x_to_y vs replace_x_with_y.

This is my first commit to rust-analyzer :D Thank you `@matklad` for your awesome Explaining rust-analyzer series <3

Closes #10214 

Co-authored-by: Andrzej Głuszak <[email protected]>

Author: bors[bot]

crates/ide_assists/src/handlers/convert_while_to_loop.rs

@@ -0,0 +1,189 @@
+use std::iter::once;
+
+use syntax::{
+    ast::{
+        self,
+        edit::{AstNodeEdit, IndentLevel},
+        make, LoopBodyOwner,
+    },
+    AstNode, T,
+};
+
+use crate::{
+    assist_context::{AssistContext, Assists},
+    utils::invert_boolean_expression,
+    AssistId, AssistKind,
+};
+
+// Assist: convert_while_to_loop
+//
+// Replace a while with a loop.
+//
+// ```
+// fn main() {
+//     $0while cond {
+//         foo();
+//     }
+// }
+// ```
+// ->
+// ```
+// fn main() {
+//     loop {
+//         if !cond {
+//             break;
+//         }
+//         foo();
+//     }
+// }
+// ```
+pub(crate) fn convert_while_to_loop(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let while_kw = ctx.find_token_syntax_at_offset(T![while])?;
+    let while_expr: ast::WhileExpr = while_kw.parent().and_then(ast::WhileExpr::cast)?;
+    let while_body = while_expr.loop_body()?;
+    let cond = while_expr.condition()?;
+
+    // Don't handle while let
+    if let Some(_) = cond.pat() {
+        return None;
+    };
+
+    let cond_expr = cond.expr()?;
+
+    let target = while_expr.syntax().text_range();
+    acc.add(
+        AssistId("convert_while_to_loop", AssistKind::RefactorRewrite),
+        "Convert while to loop",
+        target,
+        |edit| {
+            let while_indent_level = IndentLevel::from_node(while_expr.syntax());
+
+            let replacement = {
+                let if_expr = {
+                    let cond = invert_boolean_expression(cond_expr);
+                    let then_branch = make::block_expr(
+                        once(make::expr_stmt(make::expr_break(None)).into()),
+                        None,
+                    );
+
+                    make::expr_if(make::condition(cond, None), then_branch, None)
+                };
+
+                let if_expr = if_expr.indent(while_indent_level);
+                let stmts = once(make::expr_stmt(if_expr).into()).chain(while_body.statements());
+
+                let block_expr = make::block_expr(stmts, while_body.tail_expr());
+
+                let block_expr = block_expr.indent(while_indent_level);
+
+                make::expr_loop(block_expr)
+            };
+
+            edit.replace(target, replacement.syntax().text())
+        },
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_assist, check_assist_not_applicable};
+
+    use super::*;
+
+    #[test]
+    fn convert_inside_fn() {
+        check_assist(
+            convert_while_to_loop,
+            r#"
+fn main() {
+    while$0 cond {
+        foo();
+    }
+}
+"#,
+            r#"
+fn main() {
+    loop {
+        if !cond {
+            break;
+        }
+        foo();
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn convert_busy_wait() {
+        check_assist(
+            convert_while_to_loop,
+            r#"
+fn main() {
+    while$0 cond() {}
+}
+"#,
+            r#"
+fn main() {
+    loop {
+        if !cond() {
+            break;
+        }
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn convert_trailing_expr() {
+        check_assist(
+            convert_while_to_loop,
+            r#"
+fn main() {
+    while$0 cond() {
+        bar()
+    }
+}
+"#,
+            r#"
+fn main() {
+    loop {
+        if !cond() {
+            break;
+        }
+        bar()
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn ignore_while_let() {
+        check_assist_not_applicable(
+            convert_while_to_loop,
+            r#"
+fn main() {
+    while$0 let Some(_) = foo() {
+        bar();
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn ignore_cursor_in_body() {
+        check_assist_not_applicable(
+            convert_while_to_loop,
+            r#"
+fn main() {
+    while cond {$0
+        bar();
+    }
+}
+"#,
+        );
+    }
+}

crates/ide_assists/src/lib.rs

@@ -118,6 +118,7 @@ mod handlers {
     mod convert_iter_for_each_to_for;
     mod convert_tuple_struct_to_named_struct;
     mod convert_to_guarded_return;
+    mod convert_while_to_loop;
     mod destructure_tuple_binding;
     mod expand_glob_import;
     mod extract_function;
@@ -191,6 +192,7 @@ mod handlers {
             convert_iter_for_each_to_for::convert_iter_for_each_to_for,
             convert_to_guarded_return::convert_to_guarded_return,
             convert_tuple_struct_to_named_struct::convert_tuple_struct_to_named_struct,
+            convert_while_to_loop::convert_while_to_loop,
             destructure_tuple_binding::destructure_tuple_binding,
             expand_glob_import::expand_glob_import,
             extract_struct_from_enum_variant::extract_struct_from_enum_variant,

crates/ide_assists/src/tests/generated.rs

@@ -367,6 +367,30 @@ impl Point {
     )
 }
 
+#[test]
+fn doctest_convert_while_to_loop() {
+    check_doc_test(
+        "convert_while_to_loop",
+        r#####"
+fn main() {
+    $0while cond {
+        foo();
+    }
+}
+"#####,
+        r#####"
+fn main() {
+    loop {
+        if !cond {
+            break;
+        }
+        foo();
+    }
+}
+"#####,
+    )
+}
+
 #[test]
 fn doctest_destructure_tuple_binding() {
     check_doc_test(

crates/syntax/src/ast/make.rs

@@ -316,6 +316,11 @@ pub fn expr_if(
 pub fn expr_for_loop(pat: ast::Pat, expr: ast::Expr, block: ast::BlockExpr) -> ast::Expr {
     expr_from_text(&format!("for {} in {} {}", pat, expr, block))
 }
+
+pub fn expr_loop(block: ast::BlockExpr) -> ast::Expr {
+    expr_from_text(&format!("loop {}", block))
+}
+
 pub fn expr_prefix(op: SyntaxKind, expr: ast::Expr) -> ast::Expr {
     let token = token(op);
     expr_from_text(&format!("{}{}", token, expr))