src/overflow.rs

   1 //! Rewrite a list some items with overflow.
   2
   3 use std::cmp::min;
   4
   5 use itertools::Itertools;
   6 use rustc_ast::token::DelimToken;
   7 use rustc_ast::{ast, ptr};
   8 use rustc_span::Span;
   9
  10 use crate::closures;
  11 use crate::config::lists::*;
  12 use crate::config::Version;
  13 use crate::expr::{
  14     can_be_overflowed_expr, is_every_expr_simple, is_method_call, is_nested_call, is_simple_expr,
  15     rewrite_cond,
  16 };
  17 use crate::lists::{
  18     definitive_tactic, itemize_list, write_list, ListFormatting, ListItem, Separator,
  19 };
  20 use crate::macros::MacroArg;
  21 use crate::patterns::{can_be_overflowed_pat, TuplePatField};
  22 use crate::rewrite::{Rewrite, RewriteContext};
  23 use crate::shape::Shape;
  24 use crate::source_map::SpanUtils;
  25 use crate::spanned::Spanned;
  26 use crate::types::{can_be_overflowed_type, SegmentParam};
  27 use crate::utils::{count_newlines, extra_offset, first_line_width, last_line_width, mk_sp};
  28
  29 const SHORT_ITEM_THRESHOLD: usize = 10;
  30
  31 /// A list of `format!`-like macros, that take a long format string and a list of arguments to
  32 /// format.
  33 ///
  34 /// Organized as a list of `(&str, usize)` tuples, giving the name of the macro and the number of
  35 /// arguments before the format string (none for `format!("format", ...)`, one for `assert!(result,
  36 /// "format", ...)`, two for `assert_eq!(left, right, "format", ...)`).
  37 const SPECIAL_MACRO_WHITELIST: &[(&str, usize)] = &[
  38     // format! like macros
  39     // From the Rust Standard Library.
  40     ("eprint!", 0),
  41     ("eprintln!", 0),
  42     ("format!", 0),
  43     ("format_args!", 0),
  44     ("print!", 0),
  45     ("println!", 0),
  46     ("panic!", 0),
  47     ("unreachable!", 0),
  48     // From the `log` crate.
  49     ("debug!", 0),
  50     ("error!", 0),
  51     ("info!", 0),
  52     ("warn!", 0),
  53     // write! like macros
  54     ("assert!", 1),
  55     ("debug_assert!", 1),
  56     ("write!", 1),
  57     ("writeln!", 1),
  58     // assert_eq! like macros
  59     ("assert_eq!", 2),
  60     ("assert_ne!", 2),
  61     ("debug_assert_eq!", 2),
  62     ("debug_assert_ne!", 2),
  63 ];
  64
  65 const SPECIAL_ATTR_WHITELIST: &[(&str, usize)] = &[
  66     // From the `failure` crate.
  67     ("fail", 0),
  68 ];
  69
  70 #[derive(Debug)]
  71 pub(crate) enum OverflowableItem<'a> {
  72     Expr(&'a ast::Expr),
  73     GenericParam(&'a ast::GenericParam),
  74     MacroArg(&'a MacroArg),
  75     NestedMetaItem(&'a ast::NestedMetaItem),
  76     SegmentParam(&'a SegmentParam<'a>),
  77     FieldDef(&'a ast::FieldDef),
  78     TuplePatField(&'a TuplePatField<'a>),
  79     Ty(&'a ast::Ty),
  80 }
  81
  82 impl<'a> Rewrite for OverflowableItem<'a> {
  83     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
  84         self.map(|item| item.rewrite(context, shape))
  85     }
  86 }
  87
  88 impl<'a> Spanned for OverflowableItem<'a> {
  89     fn span(&self) -> Span {
  90         self.map(|item| item.span())
  91     }
  92 }
  93
  94 impl<'a> OverflowableItem<'a> {
  95     fn has_attrs(&self) -> bool {
  96         match self {
  97             OverflowableItem::Expr(ast::Expr { attrs, .. })
  98             | OverflowableItem::GenericParam(ast::GenericParam { attrs, .. }) => !attrs.is_empty(),
  99             OverflowableItem::FieldDef(ast::FieldDef { attrs, .. }) => !attrs.is_empty(),
 100             OverflowableItem::MacroArg(MacroArg::Expr(expr)) => !expr.attrs.is_empty(),
 101             OverflowableItem::MacroArg(MacroArg::Item(item)) => !item.attrs.is_empty(),
 102             _ => false,
 103         }
 104     }
 105
 106     pub(crate) fn map<F, T>(&self, f: F) -> T
 107     where
 108         F: Fn(&dyn IntoOverflowableItem<'a>) -> T,
 109     {
 110         match self {
 111             OverflowableItem::Expr(expr) => f(*expr),
 112             OverflowableItem::GenericParam(gp) => f(*gp),
 113             OverflowableItem::MacroArg(macro_arg) => f(*macro_arg),
 114             OverflowableItem::NestedMetaItem(nmi) => f(*nmi),
 115             OverflowableItem::SegmentParam(sp) => f(*sp),
 116             OverflowableItem::FieldDef(sf) => f(*sf),
 117             OverflowableItem::TuplePatField(pat) => f(*pat),
 118             OverflowableItem::Ty(ty) => f(*ty),
 119         }
 120     }
 121
 122     pub(crate) fn is_simple(&self) -> bool {
 123         match self {
 124             OverflowableItem::Expr(expr) => is_simple_expr(expr),
 125             OverflowableItem::MacroArg(MacroArg::Keyword(..)) => true,
 126             OverflowableItem::MacroArg(MacroArg::Expr(expr)) => is_simple_expr(expr),
 127             OverflowableItem::NestedMetaItem(nested_meta_item) => match nested_meta_item {
 128                 ast::NestedMetaItem::Literal(..) => true,
 129                 ast::NestedMetaItem::MetaItem(ref meta_item) => {
 130                     matches!(meta_item.kind, ast::MetaItemKind::Word)
 131                 }
 132             },
 133             _ => false,
 134         }
 135     }
 136
 137     pub(crate) fn is_expr(&self) -> bool {
 138         matches!(
 139             self,
 140             OverflowableItem::Expr(..) | OverflowableItem::MacroArg(MacroArg::Expr(..))
 141         )
 142     }
 143
 144     pub(crate) fn is_nested_call(&self) -> bool {
 145         match self {
 146             OverflowableItem::Expr(expr) => is_nested_call(expr),
 147             OverflowableItem::MacroArg(MacroArg::Expr(expr)) => is_nested_call(expr),
 148             _ => false,
 149         }
 150     }
 151
 152     pub(crate) fn to_expr(&self) -> Option<&'a ast::Expr> {
 153         match self {
 154             OverflowableItem::Expr(expr) => Some(expr),
 155             OverflowableItem::MacroArg(MacroArg::Expr(ref expr)) => Some(expr),
 156             _ => None,
 157         }
 158     }
 159
 160     pub(crate) fn can_be_overflowed(&self, context: &RewriteContext<'_>, len: usize) -> bool {
 161         match self {
 162             OverflowableItem::Expr(expr) => can_be_overflowed_expr(context, expr, len),
 163             OverflowableItem::MacroArg(macro_arg) => match macro_arg {
 164                 MacroArg::Expr(ref expr) => can_be_overflowed_expr(context, expr, len),
 165                 MacroArg::Ty(ref ty) => can_be_overflowed_type(context, ty, len),
 166                 MacroArg::Pat(..) => false,
 167                 MacroArg::Item(..) => len == 1,
 168                 MacroArg::Keyword(..) => false,
 169             },
 170             OverflowableItem::NestedMetaItem(nested_meta_item) if len == 1 => {
 171                 match nested_meta_item {
 172                     ast::NestedMetaItem::Literal(..) => false,
 173                     ast::NestedMetaItem::MetaItem(..) => true,
 174                 }
 175             }
 176             OverflowableItem::SegmentParam(SegmentParam::Type(ty)) => {
 177                 can_be_overflowed_type(context, ty, len)
 178             }
 179             OverflowableItem::TuplePatField(pat) => can_be_overflowed_pat(context, pat, len),
 180             OverflowableItem::Ty(ty) => can_be_overflowed_type(context, ty, len),
 181             _ => false,
 182         }
 183     }
 184
 185     fn whitelist(&self) -> &'static [(&'static str, usize)] {
 186         match self {
 187             OverflowableItem::MacroArg(..) => SPECIAL_MACRO_WHITELIST,
 188             OverflowableItem::NestedMetaItem(..) => SPECIAL_ATTR_WHITELIST,
 189             _ => &[],
 190         }
 191     }
 192 }
 193
 194 pub(crate) trait IntoOverflowableItem<'a>: Rewrite + Spanned {
 195     fn into_overflowable_item(&'a self) -> OverflowableItem<'a>;
 196 }
 197
 198 impl<'a, T: 'a + IntoOverflowableItem<'a>> IntoOverflowableItem<'a> for ptr::P<T> {
 199     fn into_overflowable_item(&'a self) -> OverflowableItem<'a> {
 200         (**self).into_overflowable_item()
 201     }
 202 }
 203
 204 macro_rules! impl_into_overflowable_item_for_ast_node {
 205     ($($ast_node:ident),*) => {
 206         $(
 207             impl<'a> IntoOverflowableItem<'a> for ast::$ast_node {
 208                 fn into_overflowable_item(&'a self) -> OverflowableItem<'a> {
 209                     OverflowableItem::$ast_node(self)
 210                 }
 211             }
 212         )*
 213     }
 214 }
 215
 216 macro_rules! impl_into_overflowable_item_for_rustfmt_types {
 217     ([$($ty:ident),*], [$($ty_with_lifetime:ident),*]) => {
 218         $(
 219             impl<'a> IntoOverflowableItem<'a> for $ty {
 220                 fn into_overflowable_item(&'a self) -> OverflowableItem<'a> {
 221                     OverflowableItem::$ty(self)
 222                 }
 223             }
 224         )*
 225         $(
 226             impl<'a> IntoOverflowableItem<'a> for $ty_with_lifetime<'a> {
 227                 fn into_overflowable_item(&'a self) -> OverflowableItem<'a> {
 228                     OverflowableItem::$ty_with_lifetime(self)
 229                 }
 230             }
 231         )*
 232     }
 233 }
 234
 235 impl_into_overflowable_item_for_ast_node!(Expr, GenericParam, NestedMetaItem, FieldDef, Ty);
 236 impl_into_overflowable_item_for_rustfmt_types!([MacroArg], [SegmentParam, TuplePatField]);
 237
 238 pub(crate) fn into_overflowable_list<'a, T>(
 239     iter: impl Iterator<Item = &'a T>,
 240 ) -> impl Iterator<Item = OverflowableItem<'a>>
 241 where
 242     T: 'a + IntoOverflowableItem<'a>,
 243 {
 244     iter.map(|x| IntoOverflowableItem::into_overflowable_item(x))
 245 }
 246
 247 pub(crate) fn rewrite_with_parens<'a, T: 'a + IntoOverflowableItem<'a>>(
 248     context: &'a RewriteContext<'_>,
 249     ident: &'a str,
 250     items: impl Iterator<Item = &'a T>,
 251     shape: Shape,
 252     span: Span,
 253     item_max_width: usize,
 254     force_separator_tactic: Option<SeparatorTactic>,
 255 ) -> Option<String> {
 256     Context::new(
 257         context,
 258         items,
 259         ident,
 260         shape,
 261         span,
 262         "(",
 263         ")",
 264         item_max_width,
 265         force_separator_tactic,
 266         None,
 267     )
 268     .rewrite(shape)
 269 }
 270
 271 pub(crate) fn rewrite_with_angle_brackets<'a, T: 'a + IntoOverflowableItem<'a>>(
 272     context: &'a RewriteContext<'_>,
 273     ident: &'a str,
 274     items: impl Iterator<Item = &'a T>,
 275     shape: Shape,
 276     span: Span,
 277 ) -> Option<String> {
 278     Context::new(
 279         context,
 280         items,
 281         ident,
 282         shape,
 283         span,
 284         "<",
 285         ">",
 286         context.config.max_width(),
 287         None,
 288         None,
 289     )
 290     .rewrite(shape)
 291 }
 292
 293 pub(crate) fn rewrite_with_square_brackets<'a, T: 'a + IntoOverflowableItem<'a>>(
 294     context: &'a RewriteContext<'_>,
 295     name: &'a str,
 296     items: impl Iterator<Item = &'a T>,
 297     shape: Shape,
 298     span: Span,
 299     force_separator_tactic: Option<SeparatorTactic>,
 300     delim_token: Option<DelimToken>,
 301 ) -> Option<String> {
 302     let (lhs, rhs) = match delim_token {
 303         Some(DelimToken::Paren) => ("(", ")"),
 304         Some(DelimToken::Brace) => ("{", "}"),
 305         _ => ("[", "]"),
 306     };
 307     Context::new(
 308         context,
 309         items,
 310         name,
 311         shape,
 312         span,
 313         lhs,
 314         rhs,
 315         context.config.array_width(),
 316         force_separator_tactic,
 317         Some(("[", "]")),
 318     )
 319     .rewrite(shape)
 320 }
 321
 322 struct Context<'a> {
 323     context: &'a RewriteContext<'a>,
 324     items: Vec<OverflowableItem<'a>>,
 325     ident: &'a str,
 326     prefix: &'static str,
 327     suffix: &'static str,
 328     one_line_shape: Shape,
 329     nested_shape: Shape,
 330     span: Span,
 331     item_max_width: usize,
 332     one_line_width: usize,
 333     force_separator_tactic: Option<SeparatorTactic>,
 334     custom_delims: Option<(&'a str, &'a str)>,
 335 }
 336
 337 impl<'a> Context<'a> {
 338     fn new<T: 'a + IntoOverflowableItem<'a>>(
 339         context: &'a RewriteContext<'_>,
 340         items: impl Iterator<Item = &'a T>,
 341         ident: &'a str,
 342         shape: Shape,
 343         span: Span,
 344         prefix: &'static str,
 345         suffix: &'static str,
 346         item_max_width: usize,
 347         force_separator_tactic: Option<SeparatorTactic>,
 348         custom_delims: Option<(&'a str, &'a str)>,
 349     ) -> Context<'a> {
 350         let used_width = extra_offset(ident, shape);
 351         // 1 = `()`
 352         let one_line_width = shape.width.saturating_sub(used_width + 2);
 353
 354         // 1 = "(" or ")"
 355         let one_line_shape = shape
 356             .offset_left(last_line_width(ident) + 1)
 357             .and_then(|shape| shape.sub_width(1))
 358             .unwrap_or(Shape { width: 0, ..shape });
 359         let nested_shape = shape_from_indent_style(context, shape, used_width + 2, used_width + 1);
 360         Context {
 361             context,
 362             items: into_overflowable_list(items).collect(),
 363             ident,
 364             one_line_shape,
 365             nested_shape,
 366             span,
 367             prefix,
 368             suffix,
 369             item_max_width,
 370             one_line_width,
 371             force_separator_tactic,
 372             custom_delims,
 373         }
 374     }
 375
 376     fn last_item(&self) -> Option<&OverflowableItem<'_>> {
 377         self.items.last()
 378     }
 379
 380     fn items_span(&self) -> Span {
 381         let span_lo = self
 382             .context
 383             .snippet_provider
 384             .span_after(self.span, self.prefix);
 385         mk_sp(span_lo, self.span.hi())
 386     }
 387
 388     fn rewrite_last_item_with_overflow(
 389         &self,
 390         last_list_item: &mut ListItem,
 391         shape: Shape,
 392     ) -> Option<String> {
 393         let last_item = self.last_item()?;
 394         let rewrite = match last_item {
 395             OverflowableItem::Expr(ref expr) => {
 396                 match expr.kind {
 397                     // When overflowing the closure which consists of a single control flow
 398                     // expression, force to use block if its condition uses multi line.
 399                     ast::ExprKind::Closure(..) => {
 400                         // If the argument consists of multiple closures, we do not overflow
 401                         // the last closure.
 402                         if closures::args_have_many_closure(&self.items) {
 403                             None
 404                         } else {
 405                             closures::rewrite_last_closure(self.context, expr, shape)
 406                         }
 407                     }
 408
 409                     // When overflowing the expressions which consists of a control flow
 410                     // expression, avoid condition to use multi line.
 411                     ast::ExprKind::If(..)
 412                     | ast::ExprKind::ForLoop(..)
 413                     | ast::ExprKind::Loop(..)
 414                     | ast::ExprKind::While(..)
 415                     | ast::ExprKind::Match(..) => {
 416                         let multi_line = rewrite_cond(self.context, expr, shape)
 417                             .map_or(false, |cond| cond.contains('\n'));
 418
 419                         if multi_line {
 420                             None
 421                         } else {
 422                             expr.rewrite(self.context, shape)
 423                         }
 424                     }
 425
 426                     _ => expr.rewrite(self.context, shape),
 427                 }
 428             }
 429             item => item.rewrite(self.context, shape),
 430         };
 431
 432         if let Some(rewrite) = rewrite {
 433             // splitn(2, *).next().unwrap() is always safe.
 434             let rewrite_first_line = Some(rewrite.splitn(2, '\n').next().unwrap().to_owned());
 435             last_list_item.item = rewrite_first_line;
 436             Some(rewrite)
 437         } else {
 438             None
 439         }
 440     }
 441
 442     fn default_tactic(&self, list_items: &[ListItem]) -> DefinitiveListTactic {
 443         definitive_tactic(
 444             list_items,
 445             ListTactic::LimitedHorizontalVertical(self.item_max_width),
 446             Separator::Comma,
 447             self.one_line_width,
 448         )
 449     }
 450
 451     fn try_overflow_last_item(&self, list_items: &mut Vec<ListItem>) -> DefinitiveListTactic {
 452         // 1 = "("
 453         let combine_arg_with_callee = self.items.len() == 1
 454             && self.items[0].is_expr()
 455             && !self.items[0].has_attrs()
 456             && self.ident.len() < self.context.config.tab_spaces();
 457         let overflow_last = combine_arg_with_callee || can_be_overflowed(self.context, &self.items);
 458
 459         // Replace the last item with its first line to see if it fits with
 460         // first arguments.
 461         let placeholder = if overflow_last {
 462             let old_value = self.context.force_one_line_chain.get();
 463             match self.last_item() {
 464                 Some(OverflowableItem::Expr(expr))
 465                     if !combine_arg_with_callee && is_method_call(expr) =>
 466                 {
 467                     self.context.force_one_line_chain.replace(true);
 468                 }
 469                 Some(OverflowableItem::MacroArg(MacroArg::Expr(expr)))
 470                     if !combine_arg_with_callee
 471                         && is_method_call(expr)
 472                         && self.context.config.version() == Version::Two =>
 473                 {
 474                     self.context.force_one_line_chain.replace(true);
 475                 }
 476                 _ => (),
 477             }
 478             let result = last_item_shape(
 479                 &self.items,
 480                 list_items,
 481                 self.one_line_shape,
 482                 self.item_max_width,
 483             )
 484             .and_then(|arg_shape| {
 485                 self.rewrite_last_item_with_overflow(
 486                     &mut list_items[self.items.len() - 1],
 487                     arg_shape,
 488                 )
 489             });
 490             self.context.force_one_line_chain.replace(old_value);
 491             result
 492         } else {
 493             None
 494         };
 495
 496         let mut tactic = definitive_tactic(
 497             &*list_items,
 498             ListTactic::LimitedHorizontalVertical(self.item_max_width),
 499             Separator::Comma,
 500             self.one_line_width,
 501         );
 502
 503         // Replace the stub with the full overflowing last argument if the rewrite
 504         // succeeded and its first line fits with the other arguments.
 505         match (overflow_last, tactic, placeholder) {
 506             (true, DefinitiveListTactic::Horizontal, Some(ref overflowed))
 507                 if self.items.len() == 1 =>
 508             {
 509                 // When we are rewriting a nested function call, we restrict the
 510                 // budget for the inner function to avoid them being deeply nested.
 511                 // However, when the inner function has a prefix or a suffix
 512                 // (e.g., `foo() as u32`), this budget reduction may produce poorly
 513                 // formatted code, where a prefix or a suffix being left on its own
 514                 // line. Here we explicitlly check those cases.
 515                 if count_newlines(overflowed) == 1 {
 516                     let rw = self
 517                         .items
 518                         .last()
 519                         .and_then(|last_item| last_item.rewrite(self.context, self.nested_shape));
 520                     let no_newline = rw.as_ref().map_or(false, |s| !s.contains('\n'));
 521                     if no_newline {
 522                         list_items[self.items.len() - 1].item = rw;
 523                     } else {
 524                         list_items[self.items.len() - 1].item = Some(overflowed.to_owned());
 525                     }
 526                 } else {
 527                     list_items[self.items.len() - 1].item = Some(overflowed.to_owned());
 528                 }
 529             }
 530             (true, DefinitiveListTactic::Horizontal, placeholder @ Some(..)) => {
 531                 list_items[self.items.len() - 1].item = placeholder;
 532             }
 533             _ if !self.items.is_empty() => {
 534                 list_items[self.items.len() - 1].item = self
 535                     .items
 536                     .last()
 537                     .and_then(|last_item| last_item.rewrite(self.context, self.nested_shape));
 538
 539                 // Use horizontal layout for a function with a single argument as long as
 540                 // everything fits in a single line.
 541                 // `self.one_line_width == 0` means vertical layout is forced.
 542                 if self.items.len() == 1
 543                     && self.one_line_width != 0
 544                     && !list_items[0].has_comment()
 545                     && !list_items[0].inner_as_ref().contains('\n')
 546                     && crate::lists::total_item_width(&list_items[0]) <= self.one_line_width
 547                 {
 548                     tactic = DefinitiveListTactic::Horizontal;
 549                 } else {
 550                     tactic = self.default_tactic(list_items);
 551
 552                     if tactic == DefinitiveListTactic::Vertical {
 553                         if let Some((all_simple, num_args_before)) =
 554                             maybe_get_args_offset(self.ident, &self.items)
 555                         {
 556                             let one_line = all_simple
 557                                 && definitive_tactic(
 558                                     &list_items[..num_args_before],
 559                                     ListTactic::HorizontalVertical,
 560                                     Separator::Comma,
 561                                     self.nested_shape.width,
 562                                 ) == DefinitiveListTactic::Horizontal
 563                                 && definitive_tactic(
 564                                     &list_items[num_args_before + 1..],
 565                                     ListTactic::HorizontalVertical,
 566                                     Separator::Comma,
 567                                     self.nested_shape.width,
 568                                 ) == DefinitiveListTactic::Horizontal;
 569
 570                             if one_line {
 571                                 tactic = DefinitiveListTactic::SpecialMacro(num_args_before);
 572                             };
 573                         } else if is_every_expr_simple(&self.items) && no_long_items(list_items) {
 574                             tactic = DefinitiveListTactic::Mixed;
 575                         }
 576                     }
 577                 }
 578             }
 579             _ => (),
 580         }
 581
 582         tactic
 583     }
 584
 585     fn rewrite_items(&self) -> Option<(bool, String)> {
 586         let span = self.items_span();
 587         let items = itemize_list(
 588             self.context.snippet_provider,
 589             self.items.iter(),
 590             self.suffix,
 591             ",",
 592             |item| item.span().lo(),
 593             |item| item.span().hi(),
 594             |item| item.rewrite(self.context, self.nested_shape),
 595             span.lo(),
 596             span.hi(),
 597             true,
 598         );
 599         let mut list_items: Vec<_> = items.collect();
 600
 601         // Try letting the last argument overflow to the next line with block
 602         // indentation. If its first line fits on one line with the other arguments,
 603         // we format the function arguments horizontally.
 604         let tactic = self.try_overflow_last_item(&mut list_items);
 605         let trailing_separator = if let Some(tactic) = self.force_separator_tactic {
 606             tactic
 607         } else if !self.context.use_block_indent() {
 608             SeparatorTactic::Never
 609         } else {
 610             self.context.config.trailing_comma()
 611         };
 612         let ends_with_newline = match tactic {
 613             DefinitiveListTactic::Vertical | DefinitiveListTactic::Mixed => {
 614                 self.context.use_block_indent()
 615             }
 616             _ => false,
 617         };
 618
 619         let fmt = ListFormatting::new(self.nested_shape, self.context.config)
 620             .tactic(tactic)
 621             .trailing_separator(trailing_separator)
 622             .ends_with_newline(ends_with_newline);
 623
 624         write_list(&list_items, &fmt)
 625             .map(|items_str| (tactic == DefinitiveListTactic::Horizontal, items_str))
 626     }
 627
 628     fn wrap_items(&self, items_str: &str, shape: Shape, is_extendable: bool) -> String {
 629         let shape = Shape {
 630             width: shape.width.saturating_sub(last_line_width(self.ident)),
 631             ..shape
 632         };
 633
 634         let (prefix, suffix) = match self.custom_delims {
 635             Some((lhs, rhs)) => (lhs, rhs),
 636             _ => (self.prefix, self.suffix),
 637         };
 638
 639         let extend_width = if items_str.is_empty() {
 640             2
 641         } else {
 642             first_line_width(items_str) + 1
 643         };
 644         let nested_indent_str = self
 645             .nested_shape
 646             .indent
 647             .to_string_with_newline(self.context.config);
 648         let indent_str = shape
 649             .block()
 650             .indent
 651             .to_string_with_newline(self.context.config);
 652         let mut result = String::with_capacity(
 653             self.ident.len() + items_str.len() + 2 + indent_str.len() + nested_indent_str.len(),
 654         );
 655         result.push_str(self.ident);
 656         result.push_str(prefix);
 657         let force_single_line = if self.context.config.version() == Version::Two {
 658             !self.context.use_block_indent() || (is_extendable && extend_width <= shape.width)
 659         } else {
 660             // 2 = `()`
 661             let fits_one_line = items_str.len() + 2 <= shape.width;
 662             !self.context.use_block_indent()
 663                 || (self.context.inside_macro() && !items_str.contains('\n') && fits_one_line)
 664                 || (is_extendable && extend_width <= shape.width)
 665         };
 666         if force_single_line {
 667             result.push_str(items_str);
 668         } else {
 669             if !items_str.is_empty() {
 670                 result.push_str(&nested_indent_str);
 671                 result.push_str(items_str);
 672             }
 673             result.push_str(&indent_str);
 674         }
 675         result.push_str(suffix);
 676         result
 677     }
 678
 679     fn rewrite(&self, shape: Shape) -> Option<String> {
 680         let (extendable, items_str) = self.rewrite_items()?;
 681
 682         // If we are using visual indent style and failed to format, retry with block indent.
 683         if !self.context.use_block_indent()
 684             && need_block_indent(&items_str, self.nested_shape)
 685             && !extendable
 686         {
 687             self.context.use_block.replace(true);
 688             let result = self.rewrite(shape);
 689             self.context.use_block.replace(false);
 690             return result;
 691         }
 692
 693         Some(self.wrap_items(&items_str, shape, extendable))
 694     }
 695 }
 696
 697 fn need_block_indent(s: &str, shape: Shape) -> bool {
 698     s.lines().skip(1).any(|s| {
 699         s.find(|c| !char::is_whitespace(c))
 700             .map_or(false, |w| w + 1 < shape.indent.width())
 701     })
 702 }
 703
 704 fn can_be_overflowed(context: &RewriteContext<'_>, items: &[OverflowableItem<'_>]) -> bool {
 705     items
 706         .last()
 707         .map_or(false, |x| x.can_be_overflowed(context, items.len()))
 708 }
 709
 710 /// Returns a shape for the last argument which is going to be overflowed.
 711 fn last_item_shape(
 712     lists: &[OverflowableItem<'_>],
 713     items: &[ListItem],
 714     shape: Shape,
 715     args_max_width: usize,
 716 ) -> Option<Shape> {
 717     if items.len() == 1 && !lists.get(0)?.is_nested_call() {
 718         return Some(shape);
 719     }
 720     let offset = items
 721         .iter()
 722         .dropping_back(1)
 723         .map(|i| {
 724             // 2 = ", "
 725             2 + i.inner_as_ref().len()
 726         })
 727         .sum();
 728     Shape {
 729         width: min(args_max_width, shape.width),
 730         ..shape
 731     }
 732     .offset_left(offset)
 733 }
 734
 735 fn shape_from_indent_style(
 736     context: &RewriteContext<'_>,
 737     shape: Shape,
 738     overhead: usize,
 739     offset: usize,
 740 ) -> Shape {
 741     let (shape, overhead) = if context.use_block_indent() {
 742         let shape = shape
 743             .block()
 744             .block_indent(context.config.tab_spaces())
 745             .with_max_width(context.config);
 746         (shape, 1) // 1 = ","
 747     } else {
 748         (shape.visual_indent(offset), overhead)
 749     };
 750     Shape {
 751         width: shape.width.saturating_sub(overhead),
 752         ..shape
 753     }
 754 }
 755
 756 fn no_long_items(list: &[ListItem]) -> bool {
 757     list.iter()
 758         .all(|item| item.inner_as_ref().len() <= SHORT_ITEM_THRESHOLD)
 759 }
 760
 761 /// In case special-case style is required, returns an offset from which we start horizontal layout.
 762 pub(crate) fn maybe_get_args_offset(
 763     callee_str: &str,
 764     args: &[OverflowableItem<'_>],
 765 ) -> Option<(bool, usize)> {
 766     if let Some(&(_, num_args_before)) = args
 767         .get(0)?
 768         .whitelist()
 769         .iter()
 770         .find(|&&(s, _)| s == callee_str)
 771     {
 772         let all_simple = args.len() > num_args_before
 773             && is_every_expr_simple(&args[0..num_args_before])
 774             && is_every_expr_simple(&args[num_args_before + 1..]);
 775
 776         Some((all_simple, num_args_before))
 777     } else {
 778         None
 779     }
 780 }