src/tools/rustfmt/src/closures.rs

   1 use rustc_ast::{ast, ptr};
   2 use rustc_span::Span;
   3
   4 use crate::attr::get_attrs_from_stmt;
   5 use crate::config::lists::*;
   6 use crate::config::Version;
   7 use crate::expr::{block_contains_comment, is_simple_block, is_unsafe_block, rewrite_cond};
   8 use crate::items::{span_hi_for_param, span_lo_for_param};
   9 use crate::lists::{definitive_tactic, itemize_list, write_list, ListFormatting, Separator};
  10 use crate::overflow::OverflowableItem;
  11 use crate::rewrite::{Rewrite, RewriteContext};
  12 use crate::shape::Shape;
  13 use crate::source_map::SpanUtils;
  14 use crate::types::rewrite_lifetime_param;
  15 use crate::utils::{last_line_width, left_most_sub_expr, stmt_expr, NodeIdExt};
  16
  17 // This module is pretty messy because of the rules around closures and blocks:
  18 // FIXME - the below is probably no longer true in full.
  19 //   * if there is a return type, then there must be braces,
  20 //   * given a closure with braces, whether that is parsed to give an inner block
  21 //     or not depends on if there is a return type and if there are statements
  22 //     in that block,
  23 //   * if the first expression in the body ends with a block (i.e., is a
  24 //     statement without needing a semi-colon), then adding or removing braces
  25 //     can change whether it is treated as an expression or statement.
  26
  27 pub(crate) fn rewrite_closure(
  28     binder: &ast::ClosureBinder,
  29     constness: ast::Const,
  30     capture: ast::CaptureBy,
  31     is_async: &ast::Async,
  32     movability: ast::Movability,
  33     fn_decl: &ast::FnDecl,
  34     body: &ast::Expr,
  35     span: Span,
  36     context: &RewriteContext<'_>,
  37     shape: Shape,
  38 ) -> Option<String> {
  39     debug!("rewrite_closure {:?}", body);
  40
  41     let (prefix, extra_offset) = rewrite_closure_fn_decl(
  42         binder, constness, capture, is_async, movability, fn_decl, body, span, context, shape,
  43     )?;
  44     // 1 = space between `|...|` and body.
  45     let body_shape = shape.offset_left(extra_offset)?;
  46
  47     if let ast::ExprKind::Block(ref block, _) = body.kind {
  48         // The body of the closure is an empty block.
  49         if block.stmts.is_empty() && !block_contains_comment(context, block) {
  50             return body
  51                 .rewrite(context, shape)
  52                 .map(|s| format!("{} {}", prefix, s));
  53         }
  54
  55         let result = match fn_decl.output {
  56             ast::FnRetTy::Default(_) if !context.inside_macro() => {
  57                 try_rewrite_without_block(body, &prefix, context, shape, body_shape)
  58             }
  59             _ => None,
  60         };
  61
  62         result.or_else(|| {
  63             // Either we require a block, or tried without and failed.
  64             rewrite_closure_block(block, &prefix, context, body_shape)
  65         })
  66     } else {
  67         rewrite_closure_expr(body, &prefix, context, body_shape).or_else(|| {
  68             // The closure originally had a non-block expression, but we can't fit on
  69             // one line, so we'll insert a block.
  70             rewrite_closure_with_block(body, &prefix, context, body_shape)
  71         })
  72     }
  73 }
  74
  75 fn try_rewrite_without_block(
  76     expr: &ast::Expr,
  77     prefix: &str,
  78     context: &RewriteContext<'_>,
  79     shape: Shape,
  80     body_shape: Shape,
  81 ) -> Option<String> {
  82     let expr = get_inner_expr(expr, prefix, context);
  83
  84     if is_block_closure_forced(context, expr) {
  85         rewrite_closure_with_block(expr, prefix, context, shape)
  86     } else {
  87         rewrite_closure_expr(expr, prefix, context, body_shape)
  88     }
  89 }
  90
  91 fn get_inner_expr<'a>(
  92     expr: &'a ast::Expr,
  93     prefix: &str,
  94     context: &RewriteContext<'_>,
  95 ) -> &'a ast::Expr {
  96     if let ast::ExprKind::Block(ref block, _) = expr.kind {
  97         if !needs_block(block, prefix, context) {
  98             // block.stmts.len() == 1 except with `|| {{}}`;
  99             // https://github.com/rust-lang/rustfmt/issues/3844
 100             if let Some(expr) = block.stmts.first().and_then(stmt_expr) {
 101                 return get_inner_expr(expr, prefix, context);
 102             }
 103         }
 104     }
 105
 106     expr
 107 }
 108
 109 // Figure out if a block is necessary.
 110 fn needs_block(block: &ast::Block, prefix: &str, context: &RewriteContext<'_>) -> bool {
 111     let has_attributes = block.stmts.first().map_or(false, |first_stmt| {
 112         !get_attrs_from_stmt(first_stmt).is_empty()
 113     });
 114
 115     is_unsafe_block(block)
 116         || block.stmts.len() > 1
 117         || has_attributes
 118         || block_contains_comment(context, block)
 119         || prefix.contains('\n')
 120 }
 121
 122 fn veto_block(e: &ast::Expr) -> bool {
 123     match e.kind {
 124         ast::ExprKind::Call(..)
 125         | ast::ExprKind::Binary(..)
 126         | ast::ExprKind::Cast(..)
 127         | ast::ExprKind::Type(..)
 128         | ast::ExprKind::Assign(..)
 129         | ast::ExprKind::AssignOp(..)
 130         | ast::ExprKind::Field(..)
 131         | ast::ExprKind::Index(..)
 132         | ast::ExprKind::Range(..)
 133         | ast::ExprKind::Try(..) => true,
 134         _ => false,
 135     }
 136 }
 137
 138 // Rewrite closure with a single expression wrapping its body with block.
 139 // || { #[attr] foo() } -> Block { #[attr] foo() }
 140 fn rewrite_closure_with_block(
 141     body: &ast::Expr,
 142     prefix: &str,
 143     context: &RewriteContext<'_>,
 144     shape: Shape,
 145 ) -> Option<String> {
 146     let left_most = left_most_sub_expr(body);
 147     let veto_block = veto_block(body) && !expr_requires_semi_to_be_stmt(left_most);
 148     if veto_block {
 149         return None;
 150     }
 151
 152     let block = ast::Block {
 153         stmts: vec![ast::Stmt {
 154             id: ast::NodeId::root(),
 155             kind: ast::StmtKind::Expr(ptr::P(body.clone())),
 156             span: body.span,
 157         }],
 158         id: ast::NodeId::root(),
 159         rules: ast::BlockCheckMode::Default,
 160         tokens: None,
 161         span: body
 162             .attrs
 163             .first()
 164             .map(|attr| attr.span.to(body.span))
 165             .unwrap_or(body.span),
 166         could_be_bare_literal: false,
 167     };
 168     let block = crate::expr::rewrite_block_with_visitor(
 169         context,
 170         "",
 171         &block,
 172         Some(&body.attrs),
 173         None,
 174         shape,
 175         false,
 176     )?;
 177     Some(format!("{} {}", prefix, block))
 178 }
 179
 180 // Rewrite closure with a single expression without wrapping its body with block.
 181 fn rewrite_closure_expr(
 182     expr: &ast::Expr,
 183     prefix: &str,
 184     context: &RewriteContext<'_>,
 185     shape: Shape,
 186 ) -> Option<String> {
 187     fn allow_multi_line(expr: &ast::Expr) -> bool {
 188         match expr.kind {
 189             ast::ExprKind::Match(..)
 190             | ast::ExprKind::Async(..)
 191             | ast::ExprKind::Block(..)
 192             | ast::ExprKind::TryBlock(..)
 193             | ast::ExprKind::Loop(..)
 194             | ast::ExprKind::Struct(..) => true,
 195
 196             ast::ExprKind::AddrOf(_, _, ref expr)
 197             | ast::ExprKind::Box(ref expr)
 198             | ast::ExprKind::Try(ref expr)
 199             | ast::ExprKind::Unary(_, ref expr)
 200             | ast::ExprKind::Cast(ref expr, _) => allow_multi_line(expr),
 201
 202             _ => false,
 203         }
 204     }
 205
 206     // When rewriting closure's body without block, we require it to fit in a single line
 207     // unless it is a block-like expression or we are inside macro call.
 208     let veto_multiline = (!allow_multi_line(expr) && !context.inside_macro())
 209         || context.config.force_multiline_blocks();
 210     expr.rewrite(context, shape)
 211         .and_then(|rw| {
 212             if veto_multiline && rw.contains('\n') {
 213                 None
 214             } else {
 215                 Some(rw)
 216             }
 217         })
 218         .map(|rw| format!("{} {}", prefix, rw))
 219 }
 220
 221 // Rewrite closure whose body is block.
 222 fn rewrite_closure_block(
 223     block: &ast::Block,
 224     prefix: &str,
 225     context: &RewriteContext<'_>,
 226     shape: Shape,
 227 ) -> Option<String> {
 228     Some(format!("{} {}", prefix, block.rewrite(context, shape)?))
 229 }
 230
 231 // Return type is (prefix, extra_offset)
 232 fn rewrite_closure_fn_decl(
 233     binder: &ast::ClosureBinder,
 234     constness: ast::Const,
 235     capture: ast::CaptureBy,
 236     asyncness: &ast::Async,
 237     movability: ast::Movability,
 238     fn_decl: &ast::FnDecl,
 239     body: &ast::Expr,
 240     span: Span,
 241     context: &RewriteContext<'_>,
 242     shape: Shape,
 243 ) -> Option<(String, usize)> {
 244     let binder = match binder {
 245         ast::ClosureBinder::For { generic_params, .. } if generic_params.is_empty() => {
 246             "for<> ".to_owned()
 247         }
 248         ast::ClosureBinder::For { generic_params, .. } => {
 249             let lifetime_str = rewrite_lifetime_param(context, shape, generic_params)?;
 250             format!("for<{lifetime_str}> ")
 251         }
 252         ast::ClosureBinder::NotPresent => "".to_owned(),
 253     };
 254
 255     let const_ = if matches!(constness, ast::Const::Yes(_)) {
 256         "const "
 257     } else {
 258         ""
 259     };
 260
 261     let immovable = if movability == ast::Movability::Static {
 262         "static "
 263     } else {
 264         ""
 265     };
 266     let is_async = if asyncness.is_async() { "async " } else { "" };
 267     let mover = if capture == ast::CaptureBy::Value {
 268         "move "
 269     } else {
 270         ""
 271     };
 272     // 4 = "|| {".len(), which is overconservative when the closure consists of
 273     // a single expression.
 274     let nested_shape = shape
 275         .shrink_left(binder.len() + const_.len() + immovable.len() + is_async.len() + mover.len())?
 276         .sub_width(4)?;
 277
 278     // 1 = |
 279     let param_offset = nested_shape.indent + 1;
 280     let param_shape = nested_shape.offset_left(1)?.visual_indent(0);
 281     let ret_str = fn_decl.output.rewrite(context, param_shape)?;
 282
 283     let param_items = itemize_list(
 284         context.snippet_provider,
 285         fn_decl.inputs.iter(),
 286         "|",
 287         ",",
 288         |param| span_lo_for_param(param),
 289         |param| span_hi_for_param(context, param),
 290         |param| param.rewrite(context, param_shape),
 291         context.snippet_provider.span_after(span, "|"),
 292         body.span.lo(),
 293         false,
 294     );
 295     let item_vec = param_items.collect::<Vec<_>>();
 296     // 1 = space between parameters and return type.
 297     let horizontal_budget = nested_shape.width.saturating_sub(ret_str.len() + 1);
 298     let tactic = definitive_tactic(
 299         &item_vec,
 300         ListTactic::HorizontalVertical,
 301         Separator::Comma,
 302         horizontal_budget,
 303     );
 304     let param_shape = match tactic {
 305         DefinitiveListTactic::Horizontal => param_shape.sub_width(ret_str.len() + 1)?,
 306         _ => param_shape,
 307     };
 308
 309     let fmt = ListFormatting::new(param_shape, context.config)
 310         .tactic(tactic)
 311         .preserve_newline(true);
 312     let list_str = write_list(&item_vec, &fmt)?;
 313     let mut prefix = format!(
 314         "{}{}{}{}{}|{}|",
 315         binder, const_, immovable, is_async, mover, list_str
 316     );
 317
 318     if !ret_str.is_empty() {
 319         if prefix.contains('\n') {
 320             prefix.push('\n');
 321             prefix.push_str(&param_offset.to_string(context.config));
 322         } else {
 323             prefix.push(' ');
 324         }
 325         prefix.push_str(&ret_str);
 326     }
 327     // 1 = space between `|...|` and body.
 328     let extra_offset = last_line_width(&prefix) + 1;
 329
 330     Some((prefix, extra_offset))
 331 }
 332
 333 // Rewriting closure which is placed at the end of the function call's arg.
 334 // Returns `None` if the reformatted closure 'looks bad'.
 335 pub(crate) fn rewrite_last_closure(
 336     context: &RewriteContext<'_>,
 337     expr: &ast::Expr,
 338     shape: Shape,
 339 ) -> Option<String> {
 340     if let ast::ExprKind::Closure(ref closure) = expr.kind {
 341         let ast::Closure {
 342             ref binder,
 343             constness,
 344             capture_clause,
 345             ref asyncness,
 346             movability,
 347             ref fn_decl,
 348             ref body,
 349             fn_decl_span: _,
 350             fn_arg_span: _,
 351         } = **closure;
 352         let body = match body.kind {
 353             ast::ExprKind::Block(ref block, _)
 354                 if !is_unsafe_block(block)
 355                     && !context.inside_macro()
 356                     && is_simple_block(context, block, Some(&body.attrs)) =>
 357             {
 358                 stmt_expr(&block.stmts[0]).unwrap_or(body)
 359             }
 360             _ => body,
 361         };
 362         let (prefix, extra_offset) = rewrite_closure_fn_decl(
 363             binder,
 364             constness,
 365             capture_clause,
 366             asyncness,
 367             movability,
 368             fn_decl,
 369             body,
 370             expr.span,
 371             context,
 372             shape,
 373         )?;
 374         // If the closure goes multi line before its body, do not overflow the closure.
 375         if prefix.contains('\n') {
 376             return None;
 377         }
 378
 379         let body_shape = shape.offset_left(extra_offset)?;
 380
 381         // We force to use block for the body of the closure for certain kinds of expressions.
 382         if is_block_closure_forced(context, body) {
 383             return rewrite_closure_with_block(body, &prefix, context, body_shape).map(
 384                 |body_str| {
 385                     match fn_decl.output {
 386                         ast::FnRetTy::Default(..) if body_str.lines().count() <= 7 => {
 387                             // If the expression can fit in a single line, we need not force block
 388                             // closure.  However, if the closure has a return type, then we must
 389                             // keep the blocks.
 390                             match rewrite_closure_expr(body, &prefix, context, shape) {
 391                                 Some(single_line_body_str)
 392                                     if !single_line_body_str.contains('\n') =>
 393                                 {
 394                                     single_line_body_str
 395                                 }
 396                                 _ => body_str,
 397                             }
 398                         }
 399                         _ => body_str,
 400                     }
 401                 },
 402             );
 403         }
 404
 405         // When overflowing the closure which consists of a single control flow expression,
 406         // force to use block if its condition uses multi line.
 407         let is_multi_lined_cond = rewrite_cond(context, body, body_shape).map_or(false, |cond| {
 408             cond.contains('\n') || cond.len() > body_shape.width
 409         });
 410         if is_multi_lined_cond {
 411             return rewrite_closure_with_block(body, &prefix, context, body_shape);
 412         }
 413
 414         // Seems fine, just format the closure in usual manner.
 415         return expr.rewrite(context, shape);
 416     }
 417     None
 418 }
 419
 420 /// Returns `true` if the given vector of arguments has more than one `ast::ExprKind::Closure`.
 421 pub(crate) fn args_have_many_closure(args: &[OverflowableItem<'_>]) -> bool {
 422     args.iter()
 423         .filter_map(OverflowableItem::to_expr)
 424         .filter(|expr| matches!(expr.kind, ast::ExprKind::Closure(..)))
 425         .count()
 426         > 1
 427 }
 428
 429 fn is_block_closure_forced(context: &RewriteContext<'_>, expr: &ast::Expr) -> bool {
 430     // If we are inside macro, we do not want to add or remove block from closure body.
 431     if context.inside_macro() {
 432         false
 433     } else {
 434         is_block_closure_forced_inner(expr, context.config.version())
 435     }
 436 }
 437
 438 fn is_block_closure_forced_inner(expr: &ast::Expr, version: Version) -> bool {
 439     match expr.kind {
 440         ast::ExprKind::If(..) | ast::ExprKind::While(..) | ast::ExprKind::ForLoop(..) => true,
 441         ast::ExprKind::Loop(..) if version == Version::Two => true,
 442         ast::ExprKind::AddrOf(_, _, ref expr)
 443         | ast::ExprKind::Box(ref expr)
 444         | ast::ExprKind::Try(ref expr)
 445         | ast::ExprKind::Unary(_, ref expr)
 446         | ast::ExprKind::Cast(ref expr, _) => is_block_closure_forced_inner(expr, version),
 447         _ => false,
 448     }
 449 }
 450
 451 /// Does this expression require a semicolon to be treated
 452 /// as a statement? The negation of this: 'can this expression
 453 /// be used as a statement without a semicolon' -- is used
 454 /// as an early-bail-out in the parser so that, for instance,
 455 ///     if true {...} else {...}
 456 ///      |x| 5
 457 /// isn't parsed as (if true {...} else {...} | x) | 5
 458 // From https://github.com/rust-lang/rust/blob/master/src/libsyntax/parse/classify.rs.
 459 fn expr_requires_semi_to_be_stmt(e: &ast::Expr) -> bool {
 460     match e.kind {
 461         ast::ExprKind::If(..)
 462         | ast::ExprKind::Match(..)
 463         | ast::ExprKind::Block(..)
 464         | ast::ExprKind::While(..)
 465         | ast::ExprKind::Loop(..)
 466         | ast::ExprKind::ForLoop(..)
 467         | ast::ExprKind::TryBlock(..) => false,
 468         _ => true,
 469     }
 470 }