src/tools/rustfmt/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     Pat(&'a ast::Pat),
  81 }
  82
  83 impl<'a> Rewrite for OverflowableItem<'a> {
  84     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
  85         self.map(|item| item.rewrite(context, shape))
  86     }
  87 }
  88
  89 impl<'a> Spanned for OverflowableItem<'a> {
  90     fn span(&self) -> Span {
  91         self.map(|item| item.span())
  92     }
  93 }
  94
  95 impl<'a> OverflowableItem<'a> {
  96     fn has_attrs(&self) -> bool {
  97         match self {
  98             OverflowableItem::Expr(ast::Expr { attrs, .. })
  99             | OverflowableItem::GenericParam(ast::GenericParam { attrs, .. }) => !attrs.is_empty(),
 100             OverflowableItem::FieldDef(ast::FieldDef { attrs, .. }) => !attrs.is_empty(),
 101             OverflowableItem::MacroArg(MacroArg::Expr(expr)) => !expr.attrs.is_empty(),
 102             OverflowableItem::MacroArg(MacroArg::Item(item)) => !item.attrs.is_empty(),
 103             _ => false,
 104         }
 105     }
 106
 107     pub(crate) fn map<F, T>(&self, f: F) -> T
 108     where
 109         F: Fn(&dyn IntoOverflowableItem<'a>) -> T,
 110     {
 111         match self {
 112             OverflowableItem::Expr(expr) => f(*expr),
 113             OverflowableItem::GenericParam(gp) => f(*gp),
 114             OverflowableItem::MacroArg(macro_arg) => f(*macro_arg),
 115             OverflowableItem::NestedMetaItem(nmi) => f(*nmi),
 116             OverflowableItem::SegmentParam(sp) => f(*sp),
 117             OverflowableItem::FieldDef(sf) => f(*sf),
 118             OverflowableItem::TuplePatField(pat) => f(*pat),
 119             OverflowableItem::Ty(ty) => f(*ty),
 120             OverflowableItem::Pat(pat) => f(*pat),
 121         }
 122     }
 123
 124     pub(crate) fn is_simple(&self) -> bool {
 125         match self {
 126             OverflowableItem::Expr(expr) => is_simple_expr(expr),
 127             OverflowableItem::MacroArg(MacroArg::Keyword(..)) => true,
 128             OverflowableItem::MacroArg(MacroArg::Expr(expr)) => is_simple_expr(expr),
 129             OverflowableItem::NestedMetaItem(nested_meta_item) => match nested_meta_item {
 130                 ast::NestedMetaItem::Literal(..) => true,
 131                 ast::NestedMetaItem::MetaItem(ref meta_item) => {
 132                     matches!(meta_item.kind, ast::MetaItemKind::Word)
 133                 }
 134             },
 135             _ => false,
 136         }
 137     }
 138
 139     pub(crate) fn is_expr(&self) -> bool {
 140         matches!(
 141             self,
 142             OverflowableItem::Expr(..) | OverflowableItem::MacroArg(MacroArg::Expr(..))
 143         )
 144     }
 145
 146     pub(crate) fn is_nested_call(&self) -> bool {
 147         match self {
 148             OverflowableItem::Expr(expr) => is_nested_call(expr),
 149             OverflowableItem::MacroArg(MacroArg::Expr(expr)) => is_nested_call(expr),
 150             _ => false,
 151         }
 152     }
 153
 154     pub(crate) fn to_expr(&self) -> Option<&'a ast::Expr> {
 155         match self {
 156             OverflowableItem::Expr(expr) => Some(expr),
 157             OverflowableItem::MacroArg(MacroArg::Expr(ref expr)) => Some(expr),
 158             _ => None,
 159         }
 160     }
 161
 162     pub(crate) fn can_be_overflowed(&self, context: &RewriteContext<'_>, len: usize) -> bool {
 163         match self {
 164             OverflowableItem::Expr(expr) => can_be_overflowed_expr(context, expr, len),
 165             OverflowableItem::MacroArg(macro_arg) => match macro_arg {
 166                 MacroArg::Expr(ref expr) => can_be_overflowed_expr(context, expr, len),
 167                 MacroArg::Ty(ref ty) => can_be_overflowed_type(context, ty, len),
 168                 MacroArg::Pat(..) => false,
 169                 MacroArg::Item(..) => len == 1,
 170                 MacroArg::Keyword(..) => false,
 171             },
 172             OverflowableItem::NestedMetaItem(nested_meta_item) if len == 1 => {
 173                 match nested_meta_item {
 174                     ast::NestedMetaItem::Literal(..) => false,
 175                     ast::NestedMetaItem::MetaItem(..) => true,
 176                 }
 177             }
 178             OverflowableItem::SegmentParam(SegmentParam::Type(ty)) => {
 179                 can_be_overflowed_type(context, ty, len)
 180             }
 181             OverflowableItem::TuplePatField(pat) => can_be_overflowed_pat(context, pat, len),
 182             OverflowableItem::Ty(ty) => can_be_overflowed_type(context, ty, len),
 183             _ => false,
 184         }
 185     }
 186
 187     fn whitelist(&self) -> &'static [(&'static str, usize)] {
 188         match self {
 189             OverflowableItem::MacroArg(..) => SPECIAL_MACRO_WHITELIST,
 190             OverflowableItem::NestedMetaItem(..) => SPECIAL_ATTR_WHITELIST,
 191             _ => &[],
 192         }
 193     }
 194 }
 195
 196 pub(crate) trait IntoOverflowableItem<'a>: Rewrite + Spanned {
 197     fn into_overflowable_item(&'a self) -> OverflowableItem<'a>;
 198 }
 199
 200 impl<'a, T: 'a + IntoOverflowableItem<'a>> IntoOverflowableItem<'a> for ptr::P<T> {
 201     fn into_overflowable_item(&'a self) -> OverflowableItem<'a> {
 202         (**self).into_overflowable_item()
 203     }
 204 }
 205
 206 macro_rules! impl_into_overflowable_item_for_ast_node {
 207     ($($ast_node:ident),*) => {
 208         $(
 209             impl<'a> IntoOverflowableItem<'a> for ast::$ast_node {
 210                 fn into_overflowable_item(&'a self) -> OverflowableItem<'a> {
 211                     OverflowableItem::$ast_node(self)
 212                 }
 213             }
 214         )*
 215     }
 216 }
 217
 218 macro_rules! impl_into_overflowable_item_for_rustfmt_types {
 219     ([$($ty:ident),*], [$($ty_with_lifetime:ident),*]) => {
 220         $(
 221             impl<'a> IntoOverflowableItem<'a> for $ty {
 222                 fn into_overflowable_item(&'a self) -> OverflowableItem<'a> {
 223                     OverflowableItem::$ty(self)
 224                 }
 225             }
 226         )*
 227         $(
 228             impl<'a> IntoOverflowableItem<'a> for $ty_with_lifetime<'a> {
 229                 fn into_overflowable_item(&'a self) -> OverflowableItem<'a> {
 230                     OverflowableItem::$ty_with_lifetime(self)
 231                 }
 232             }
 233         )*
 234     }
 235 }
 236
 237 impl_into_overflowable_item_for_ast_node!(Expr, GenericParam, NestedMetaItem, FieldDef, Ty, Pat);
 238 impl_into_overflowable_item_for_rustfmt_types!([MacroArg], [SegmentParam, TuplePatField]);
 239
 240 pub(crate) fn into_overflowable_list<'a, T>(
 241     iter: impl Iterator<Item = &'a T>,
 242 ) -> impl Iterator<Item = OverflowableItem<'a>>
 243 where
 244     T: 'a + IntoOverflowableItem<'a>,
 245 {
 246     iter.map(|x| IntoOverflowableItem::into_overflowable_item(x))
 247 }
 248
 249 pub(crate) fn rewrite_with_parens<'a, T: 'a + IntoOverflowableItem<'a>>(
 250     context: &'a RewriteContext<'_>,
 251     ident: &'a str,
 252     items: impl Iterator<Item = &'a T>,
 253     shape: Shape,
 254     span: Span,
 255     item_max_width: usize,
 256     force_separator_tactic: Option<SeparatorTactic>,
 257 ) -> Option<String> {
 258     Context::new(
 259         context,
 260         items,
 261         ident,
 262         shape,
 263         span,
 264         "(",
 265         ")",
 266         item_max_width,
 267         force_separator_tactic,
 268         None,
 269     )
 270     .rewrite(shape)
 271 }
 272
 273 pub(crate) fn rewrite_with_angle_brackets<'a, T: 'a + IntoOverflowableItem<'a>>(
 274     context: &'a RewriteContext<'_>,
 275     ident: &'a str,
 276     items: impl Iterator<Item = &'a T>,
 277     shape: Shape,
 278     span: Span,
 279 ) -> Option<String> {
 280     Context::new(
 281         context,
 282         items,
 283         ident,
 284         shape,
 285         span,
 286         "<",
 287         ">",
 288         context.config.max_width(),
 289         None,
 290         None,
 291     )
 292     .rewrite(shape)
 293 }
 294
 295 pub(crate) fn rewrite_with_square_brackets<'a, T: 'a + IntoOverflowableItem<'a>>(
 296     context: &'a RewriteContext<'_>,
 297     name: &'a str,
 298     items: impl Iterator<Item = &'a T>,
 299     shape: Shape,
 300     span: Span,
 301     force_separator_tactic: Option<SeparatorTactic>,
 302     delim_token: Option<DelimToken>,
 303 ) -> Option<String> {
 304     let (lhs, rhs) = match delim_token {
 305         Some(DelimToken::Paren) => ("(", ")"),
 306         Some(DelimToken::Brace) => ("{", "}"),
 307         _ => ("[", "]"),
 308     };
 309     Context::new(
 310         context,
 311         items,
 312         name,
 313         shape,
 314         span,
 315         lhs,
 316         rhs,
 317         context.config.array_width(),
 318         force_separator_tactic,
 319         Some(("[", "]")),
 320     )
 321     .rewrite(shape)
 322 }
 323
 324 struct Context<'a> {
 325     context: &'a RewriteContext<'a>,
 326     items: Vec<OverflowableItem<'a>>,
 327     ident: &'a str,
 328     prefix: &'static str,
 329     suffix: &'static str,
 330     one_line_shape: Shape,
 331     nested_shape: Shape,
 332     span: Span,
 333     item_max_width: usize,
 334     one_line_width: usize,
 335     force_separator_tactic: Option<SeparatorTactic>,
 336     custom_delims: Option<(&'a str, &'a str)>,
 337 }
 338
 339 impl<'a> Context<'a> {
 340     fn new<T: 'a + IntoOverflowableItem<'a>>(
 341         context: &'a RewriteContext<'_>,
 342         items: impl Iterator<Item = &'a T>,
 343         ident: &'a str,
 344         shape: Shape,
 345         span: Span,
 346         prefix: &'static str,
 347         suffix: &'static str,
 348         item_max_width: usize,
 349         force_separator_tactic: Option<SeparatorTactic>,
 350         custom_delims: Option<(&'a str, &'a str)>,
 351     ) -> Context<'a> {
 352         let used_width = extra_offset(ident, shape);
 353         // 1 = `()`
 354         let one_line_width = shape.width.saturating_sub(used_width + 2);
 355
 356         // 1 = "(" or ")"
 357         let one_line_shape = shape
 358             .offset_left(last_line_width(ident) + 1)
 359             .and_then(|shape| shape.sub_width(1))
 360             .unwrap_or(Shape { width: 0, ..shape });
 361         let nested_shape = shape_from_indent_style(context, shape, used_width + 2, used_width + 1);
 362         Context {
 363             context,
 364             items: into_overflowable_list(items).collect(),
 365             ident,
 366             one_line_shape,
 367             nested_shape,
 368             span,
 369             prefix,
 370             suffix,
 371             item_max_width,
 372             one_line_width,
 373             force_separator_tactic,
 374             custom_delims,
 375         }
 376     }
 377
 378     fn last_item(&self) -> Option<&OverflowableItem<'_>> {
 379         self.items.last()
 380     }
 381
 382     fn items_span(&self) -> Span {
 383         let span_lo = self
 384             .context
 385             .snippet_provider
 386             .span_after(self.span, self.prefix);
 387         mk_sp(span_lo, self.span.hi())
 388     }
 389
 390     fn rewrite_last_item_with_overflow(
 391         &self,
 392         last_list_item: &mut ListItem,
 393         shape: Shape,
 394     ) -> Option<String> {
 395         let last_item = self.last_item()?;
 396         let rewrite = match last_item {
 397             OverflowableItem::Expr(expr) => {
 398                 match expr.kind {
 399                     // When overflowing the closure which consists of a single control flow
 400                     // expression, force to use block if its condition uses multi line.
 401                     ast::ExprKind::Closure(..) => {
 402                         // If the argument consists of multiple closures, we do not overflow
 403                         // the last closure.
 404                         if closures::args_have_many_closure(&self.items) {
 405                             None
 406                         } else {
 407                             closures::rewrite_last_closure(self.context, expr, shape)
 408                         }
 409                     }
 410
 411                     // When overflowing the expressions which consists of a control flow
 412                     // expression, avoid condition to use multi line.
 413                     ast::ExprKind::If(..)
 414                     | ast::ExprKind::ForLoop(..)
 415                     | ast::ExprKind::Loop(..)
 416                     | ast::ExprKind::While(..)
 417                     | ast::ExprKind::Match(..) => {
 418                         let multi_line = rewrite_cond(self.context, expr, shape)
 419                             .map_or(false, |cond| cond.contains('\n'));
 420
 421                         if multi_line {
 422                             None
 423                         } else {
 424                             expr.rewrite(self.context, shape)
 425                         }
 426                     }
 427
 428                     _ => expr.rewrite(self.context, shape),
 429                 }
 430             }
 431             item => item.rewrite(self.context, shape),
 432         };
 433
 434         if let Some(rewrite) = rewrite {
 435             // splitn(2, *).next().unwrap() is always safe.
 436             let rewrite_first_line = Some(rewrite.splitn(2, '\n').next().unwrap().to_owned());
 437             last_list_item.item = rewrite_first_line;
 438             Some(rewrite)
 439         } else {
 440             None
 441         }
 442     }
 443
 444     fn default_tactic(&self, list_items: &[ListItem]) -> DefinitiveListTactic {
 445         definitive_tactic(
 446             list_items,
 447             ListTactic::LimitedHorizontalVertical(self.item_max_width),
 448             Separator::Comma,
 449             self.one_line_width,
 450         )
 451     }
 452
 453     fn try_overflow_last_item(&self, list_items: &mut Vec<ListItem>) -> DefinitiveListTactic {
 454         // 1 = "("
 455         let combine_arg_with_callee = self.items.len() == 1
 456             && self.items[0].is_expr()
 457             && !self.items[0].has_attrs()
 458             && self.ident.len() < self.context.config.tab_spaces();
 459         let overflow_last = combine_arg_with_callee || can_be_overflowed(self.context, &self.items);
 460
 461         // Replace the last item with its first line to see if it fits with
 462         // first arguments.
 463         let placeholder = if overflow_last {
 464             let old_value = self.context.force_one_line_chain.get();
 465             match self.last_item() {
 466                 Some(OverflowableItem::Expr(expr))
 467                     if !combine_arg_with_callee && is_method_call(expr) =>
 468                 {
 469                     self.context.force_one_line_chain.replace(true);
 470                 }
 471                 Some(OverflowableItem::MacroArg(MacroArg::Expr(expr)))
 472                     if !combine_arg_with_callee
 473                         && is_method_call(expr)
 474                         && self.context.config.version() == Version::Two =>
 475                 {
 476                     self.context.force_one_line_chain.replace(true);
 477                 }
 478                 _ => (),
 479             }
 480             let result = last_item_shape(
 481                 &self.items,
 482                 list_items,
 483                 self.one_line_shape,
 484                 self.item_max_width,
 485             )
 486             .and_then(|arg_shape| {
 487                 self.rewrite_last_item_with_overflow(
 488                     &mut list_items[self.items.len() - 1],
 489                     arg_shape,
 490                 )
 491             });
 492             self.context.force_one_line_chain.replace(old_value);
 493             result
 494         } else {
 495             None
 496         };
 497
 498         let mut tactic = definitive_tactic(
 499             &*list_items,
 500             ListTactic::LimitedHorizontalVertical(self.item_max_width),
 501             Separator::Comma,
 502             self.one_line_width,
 503         );
 504
 505         // Replace the stub with the full overflowing last argument if the rewrite
 506         // succeeded and its first line fits with the other arguments.
 507         match (overflow_last, tactic, placeholder) {
 508             (true, DefinitiveListTactic::Horizontal, Some(ref overflowed))
 509                 if self.items.len() == 1 =>
 510             {
 511                 // When we are rewriting a nested function call, we restrict the
 512                 // budget for the inner function to avoid them being deeply nested.
 513                 // However, when the inner function has a prefix or a suffix
 514                 // (e.g., `foo() as u32`), this budget reduction may produce poorly
 515                 // formatted code, where a prefix or a suffix being left on its own
 516                 // line. Here we explicitlly check those cases.
 517                 if count_newlines(overflowed) == 1 {
 518                     let rw = self
 519                         .items
 520                         .last()
 521                         .and_then(|last_item| last_item.rewrite(self.context, self.nested_shape));
 522                     let no_newline = rw.as_ref().map_or(false, |s| !s.contains('\n'));
 523                     if no_newline {
 524                         list_items[self.items.len() - 1].item = rw;
 525                     } else {
 526                         list_items[self.items.len() - 1].item = Some(overflowed.to_owned());
 527                     }
 528                 } else {
 529                     list_items[self.items.len() - 1].item = Some(overflowed.to_owned());
 530                 }
 531             }
 532             (true, DefinitiveListTactic::Horizontal, placeholder @ Some(..)) => {
 533                 list_items[self.items.len() - 1].item = placeholder;
 534             }
 535             _ if !self.items.is_empty() => {
 536                 list_items[self.items.len() - 1].item = self
 537                     .items
 538                     .last()
 539                     .and_then(|last_item| last_item.rewrite(self.context, self.nested_shape));
 540
 541                 // Use horizontal layout for a function with a single argument as long as
 542                 // everything fits in a single line.
 543                 // `self.one_line_width == 0` means vertical layout is forced.
 544                 if self.items.len() == 1
 545                     && self.one_line_width != 0
 546                     && !list_items[0].has_comment()
 547                     && !list_items[0].inner_as_ref().contains('\n')
 548                     && crate::lists::total_item_width(&list_items[0]) <= self.one_line_width
 549                 {
 550                     tactic = DefinitiveListTactic::Horizontal;
 551                 } else {
 552                     tactic = self.default_tactic(list_items);
 553
 554                     if tactic == DefinitiveListTactic::Vertical {
 555                         if let Some((all_simple, num_args_before)) =
 556                             maybe_get_args_offset(self.ident, &self.items)
 557                         {
 558                             let one_line = all_simple
 559                                 && definitive_tactic(
 560                                     &list_items[..num_args_before],
 561                                     ListTactic::HorizontalVertical,
 562                                     Separator::Comma,
 563                                     self.nested_shape.width,
 564                                 ) == DefinitiveListTactic::Horizontal
 565                                 && definitive_tactic(
 566                                     &list_items[num_args_before + 1..],
 567                                     ListTactic::HorizontalVertical,
 568                                     Separator::Comma,
 569                                     self.nested_shape.width,
 570                                 ) == DefinitiveListTactic::Horizontal;
 571
 572                             if one_line {
 573                                 tactic = DefinitiveListTactic::SpecialMacro(num_args_before);
 574                             };
 575                         } else if is_every_expr_simple(&self.items) && no_long_items(list_items) {
 576                             tactic = DefinitiveListTactic::Mixed;
 577                         }
 578                     }
 579                 }
 580             }
 581             _ => (),
 582         }
 583
 584         tactic
 585     }
 586
 587     fn rewrite_items(&self) -> Option<(bool, String)> {
 588         let span = self.items_span();
 589         let items = itemize_list(
 590             self.context.snippet_provider,
 591             self.items.iter(),
 592             self.suffix,
 593             ",",
 594             |item| item.span().lo(),
 595             |item| item.span().hi(),
 596             |item| item.rewrite(self.context, self.nested_shape),
 597             span.lo(),
 598             span.hi(),
 599             true,
 600         );
 601         let mut list_items: Vec<_> = items.collect();
 602
 603         // Try letting the last argument overflow to the next line with block
 604         // indentation. If its first line fits on one line with the other arguments,
 605         // we format the function arguments horizontally.
 606         let tactic = self.try_overflow_last_item(&mut list_items);
 607         let trailing_separator = if let Some(tactic) = self.force_separator_tactic {
 608             tactic
 609         } else if !self.context.use_block_indent() {
 610             SeparatorTactic::Never
 611         } else {
 612             self.context.config.trailing_comma()
 613         };
 614         let ends_with_newline = match tactic {
 615             DefinitiveListTactic::Vertical | DefinitiveListTactic::Mixed => {
 616                 self.context.use_block_indent()
 617             }
 618             _ => false,
 619         };
 620
 621         let fmt = ListFormatting::new(self.nested_shape, self.context.config)
 622             .tactic(tactic)
 623             .trailing_separator(trailing_separator)
 624             .ends_with_newline(ends_with_newline);
 625
 626         write_list(&list_items, &fmt)
 627             .map(|items_str| (tactic == DefinitiveListTactic::Horizontal, items_str))
 628     }
 629
 630     fn wrap_items(&self, items_str: &str, shape: Shape, is_extendable: bool) -> String {
 631         let shape = Shape {
 632             width: shape.width.saturating_sub(last_line_width(self.ident)),
 633             ..shape
 634         };
 635
 636         let (prefix, suffix) = match self.custom_delims {
 637             Some((lhs, rhs)) => (lhs, rhs),
 638             _ => (self.prefix, self.suffix),
 639         };
 640
 641         let extend_width = if items_str.is_empty() {
 642             2
 643         } else {
 644             first_line_width(items_str) + 1
 645         };
 646         let nested_indent_str = self
 647             .nested_shape
 648             .indent
 649             .to_string_with_newline(self.context.config);
 650         let indent_str = shape
 651             .block()
 652             .indent
 653             .to_string_with_newline(self.context.config);
 654         let mut result = String::with_capacity(
 655             self.ident.len() + items_str.len() + 2 + indent_str.len() + nested_indent_str.len(),
 656         );
 657         result.push_str(self.ident);
 658         result.push_str(prefix);
 659         let force_single_line = if self.context.config.version() == Version::Two {
 660             !self.context.use_block_indent() || (is_extendable && extend_width <= shape.width)
 661         } else {
 662             // 2 = `()`
 663             let fits_one_line = items_str.len() + 2 <= shape.width;
 664             !self.context.use_block_indent()
 665                 || (self.context.inside_macro() && !items_str.contains('\n') && fits_one_line)
 666                 || (is_extendable && extend_width <= shape.width)
 667         };
 668         if force_single_line {
 669             result.push_str(items_str);
 670         } else {
 671             if !items_str.is_empty() {
 672                 result.push_str(&nested_indent_str);
 673                 result.push_str(items_str);
 674             }
 675             result.push_str(&indent_str);
 676         }
 677         result.push_str(suffix);
 678         result
 679     }
 680
 681     fn rewrite(&self, shape: Shape) -> Option<String> {
 682         let (extendable, items_str) = self.rewrite_items()?;
 683
 684         // If we are using visual indent style and failed to format, retry with block indent.
 685         if !self.context.use_block_indent()
 686             && need_block_indent(&items_str, self.nested_shape)
 687             && !extendable
 688         {
 689             self.context.use_block.replace(true);
 690             let result = self.rewrite(shape);
 691             self.context.use_block.replace(false);
 692             return result;
 693         }
 694
 695         Some(self.wrap_items(&items_str, shape, extendable))
 696     }
 697 }
 698
 699 fn need_block_indent(s: &str, shape: Shape) -> bool {
 700     s.lines().skip(1).any(|s| {
 701         s.find(|c| !char::is_whitespace(c))
 702             .map_or(false, |w| w + 1 < shape.indent.width())
 703     })
 704 }
 705
 706 fn can_be_overflowed(context: &RewriteContext<'_>, items: &[OverflowableItem<'_>]) -> bool {
 707     items
 708         .last()
 709         .map_or(false, |x| x.can_be_overflowed(context, items.len()))
 710 }
 711
 712 /// Returns a shape for the last argument which is going to be overflowed.
 713 fn last_item_shape(
 714     lists: &[OverflowableItem<'_>],
 715     items: &[ListItem],
 716     shape: Shape,
 717     args_max_width: usize,
 718 ) -> Option<Shape> {
 719     if items.len() == 1 && !lists.get(0)?.is_nested_call() {
 720         return Some(shape);
 721     }
 722     let offset = items
 723         .iter()
 724         .dropping_back(1)
 725         .map(|i| {
 726             // 2 = ", "
 727             2 + i.inner_as_ref().len()
 728         })
 729         .sum();
 730     Shape {
 731         width: min(args_max_width, shape.width),
 732         ..shape
 733     }
 734     .offset_left(offset)
 735 }
 736
 737 fn shape_from_indent_style(
 738     context: &RewriteContext<'_>,
 739     shape: Shape,
 740     overhead: usize,
 741     offset: usize,
 742 ) -> Shape {
 743     let (shape, overhead) = if context.use_block_indent() {
 744         let shape = shape
 745             .block()
 746             .block_indent(context.config.tab_spaces())
 747             .with_max_width(context.config);
 748         (shape, 1) // 1 = ","
 749     } else {
 750         (shape.visual_indent(offset), overhead)
 751     };
 752     Shape {
 753         width: shape.width.saturating_sub(overhead),
 754         ..shape
 755     }
 756 }
 757
 758 fn no_long_items(list: &[ListItem]) -> bool {
 759     list.iter()
 760         .all(|item| item.inner_as_ref().len() <= SHORT_ITEM_THRESHOLD)
 761 }
 762
 763 /// In case special-case style is required, returns an offset from which we start horizontal layout.
 764 pub(crate) fn maybe_get_args_offset(
 765     callee_str: &str,
 766     args: &[OverflowableItem<'_>],
 767 ) -> Option<(bool, usize)> {
 768     if let Some(&(_, num_args_before)) = args
 769         .get(0)?
 770         .whitelist()
 771         .iter()
 772         .find(|&&(s, _)| s == callee_str)
 773     {
 774         let all_simple = args.len() > num_args_before
 775             && is_every_expr_simple(&args[0..num_args_before])
 776             && is_every_expr_simple(&args[num_args_before + 1..]);
 777
 778         Some((all_simple, num_args_before))
 779     } else {
 780         None
 781     }
 782 }