src/chains.rs

   1 // Copyright 2015 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 /// Formatting of chained expressions, i.e. expressions which are chained by
  12 /// dots: struct and enum field access, method calls, and try shorthand (?).
  13 ///
  14 /// Instead of walking these subexpressions one-by-one, as is our usual strategy
  15 /// for expression formatting, we collect maximal sequences of these expressions
  16 /// and handle them simultaneously.
  17 ///
  18 /// Whenever possible, the entire chain is put on a single line. If that fails,
  19 /// we put each subexpression on a separate, much like the (default) function
  20 /// argument function argument strategy.
  21 ///
  22 /// Depends on config options: `chain_indent` is the indent to use for
  23 /// blocks in the parent/root/base of the chain (and the rest of the chain's
  24 /// alignment).
  25 /// E.g., `let foo = { aaaa; bbb; ccc }.bar.baz();`, we would layout for the
  26 /// following values of `chain_indent`:
  27 /// Visual:
  28 /// ```
  29 /// let foo = {
  30 ///               aaaa;
  31 ///               bbb;
  32 ///               ccc
  33 ///           }
  34 ///           .bar
  35 ///           .baz();
  36 /// ```
  37 /// Inherit:
  38 /// ```
  39 /// let foo = {
  40 ///     aaaa;
  41 ///     bbb;
  42 ///     ccc
  43 /// }
  44 /// .bar
  45 /// .baz();
  46 /// ```
  47 /// Tabbed:
  48 /// ```
  49 /// let foo = {
  50 ///         aaaa;
  51 ///         bbb;
  52 ///         ccc
  53 ///     }
  54 ///     .bar
  55 ///     .baz();
  56 /// ```
  57 ///
  58 /// If the first item in the chain is a block expression, we align the dots with
  59 /// the braces.
  60 /// Visual:
  61 /// ```
  62 /// let a = foo.bar
  63 ///            .baz()
  64 ///            .qux
  65 /// ```
  66 /// Inherit:
  67 /// ```
  68 /// let a = foo.bar
  69 /// .baz()
  70 /// .qux
  71 /// ```
  72 /// Tabbed:
  73 /// ```
  74 /// let a = foo.bar
  75 ///     .baz()
  76 ///     .qux
  77 /// ```
  78
  79 use Shape;
  80 use rewrite::{Rewrite, RewriteContext};
  81 use utils::{wrap_str, first_line_width, last_line_width};
  82 use expr::rewrite_call;
  83 use config::IndentStyle;
  84 use macros::convert_try_mac;
  85
  86 use std::cmp::min;
  87 use std::iter;
  88 use syntax::{ast, ptr};
  89 use syntax::codemap::{mk_sp, Span};
  90
  91 pub fn rewrite_chain(expr: &ast::Expr, context: &RewriteContext, shape: Shape) -> Option<String> {
  92     debug!("rewrite_chain {:?}", shape);
  93     let total_span = expr.span;
  94     let (parent, subexpr_list) = make_subexpr_list(expr, context);
  95
  96     // Bail out if the chain is just try sugar, i.e., an expression followed by
  97     // any number of `?`s.
  98     if chain_only_try(&subexpr_list) {
  99         return rewrite_try(&parent, subexpr_list.len(), context, shape);
 100     }
 101     let trailing_try_num = subexpr_list
 102         .iter()
 103         .take_while(|e| match e.node {
 104                         ast::ExprKind::Try(..) => true,
 105                         _ => false,
 106                     })
 107         .count();
 108
 109     // Parent is the first item in the chain, e.g., `foo` in `foo.bar.baz()`.
 110     let parent_shape = if is_block_expr(context, &parent, "\n") {
 111         match context.config.chain_indent() {
 112             IndentStyle::Visual => shape.visual_indent(0),
 113             IndentStyle::Block => shape.block(),
 114         }
 115     } else {
 116         shape
 117     };
 118     let parent_rewrite = try_opt!(parent.rewrite(context, parent_shape));
 119     let parent_rewrite_contains_newline = parent_rewrite.contains('\n');
 120
 121     // Decide how to layout the rest of the chain. `extend` is true if we can
 122     // put the first non-parent item on the same line as the parent.
 123     let first_subexpr_is_try = match subexpr_list.last().unwrap().node {
 124         ast::ExprKind::Try(..) => true,
 125         _ => false,
 126     };
 127     let (nested_shape, extend) = if !parent_rewrite_contains_newline && is_continuable(&parent) {
 128         let nested_shape = if first_subexpr_is_try {
 129             parent_shape.block_indent(context.config.tab_spaces())
 130         } else {
 131             chain_indent(context, shape.add_offset(parent_rewrite.len()))
 132         };
 133         (nested_shape,
 134          context.config.chain_indent() == IndentStyle::Visual ||
 135          parent_rewrite.len() <= context.config.tab_spaces())
 136     } else if is_block_expr(context, &parent, &parent_rewrite) {
 137         match context.config.chain_indent() {
 138             // Try to put the first child on the same line with parent's last line
 139             IndentStyle::Block => (parent_shape.block_indent(context.config.tab_spaces()), true),
 140             // The parent is a block, so align the rest of the chain with the closing
 141             // brace.
 142             IndentStyle::Visual => (parent_shape, false),
 143         }
 144     } else if parent_rewrite_contains_newline {
 145         (chain_indent(context, parent_shape), false)
 146     } else {
 147         (shape.block_indent(context.config.tab_spaces()), false)
 148     };
 149
 150     let other_child_shape = nested_shape.with_max_width(context.config);
 151
 152     let first_child_shape = if extend {
 153         let overhead = last_line_width(&parent_rewrite);
 154         let offset = parent_rewrite.lines().rev().next().unwrap().trim().len();
 155         match context.config.chain_indent() {
 156             IndentStyle::Visual => try_opt!(parent_shape.offset_left(overhead)),
 157             IndentStyle::Block => try_opt!(parent_shape.block().offset_left(offset)),
 158         }
 159     } else {
 160         other_child_shape
 161     };
 162     debug!("child_shapes {:?} {:?}",
 163            first_child_shape,
 164            other_child_shape);
 165
 166     let child_shape_iter =
 167         Some(first_child_shape)
 168             .into_iter()
 169             .chain(::std::iter::repeat(other_child_shape).take(subexpr_list.len() - 1));
 170     let iter = subexpr_list.iter().rev().zip(child_shape_iter);
 171     let mut rewrites = try_opt!(iter.map(|(e, shape)| {
 172                                              rewrite_chain_subexpr(e, total_span, context, shape)
 173                                          })
 174                                     .collect::<Option<Vec<_>>>());
 175
 176     // Total of all items excluding the last.
 177     let last_non_try_index = rewrites.len() - (1 + trailing_try_num);
 178     let almost_total = rewrites[..last_non_try_index]
 179         .iter()
 180         .fold(0, |a, b| a + first_line_width(b)) + parent_rewrite.len();
 181     let one_line_len = rewrites.iter().fold(0, |a, r| a + first_line_width(r)) +
 182                        parent_rewrite.len();
 183
 184     let one_line_budget = min(shape.width, context.config.chain_one_line_max());
 185     let veto_single_line = if one_line_len > one_line_budget {
 186         if rewrites.len() > 1 {
 187             true
 188         } else if rewrites.len() == 1 {
 189             context.config.chain_split_single_child() || one_line_len > shape.width
 190         } else {
 191             false
 192         }
 193     } else if context.config.take_source_hints() && subexpr_list.len() > 1 {
 194         // Look at the source code. Unless all chain elements start on the same
 195         // line, we won't consider putting them on a single line either.
 196         let last_span = context.snippet(mk_sp(subexpr_list[1].span.hi, total_span.hi));
 197         let first_span = context.snippet(subexpr_list[1].span);
 198         let last_iter = last_span.chars().take_while(|c| c.is_whitespace());
 199
 200         first_span.chars().chain(last_iter).any(|c| c == '\n')
 201     } else {
 202         false
 203     };
 204
 205     let mut fits_single_line = !veto_single_line && almost_total <= shape.width;
 206     if fits_single_line {
 207         let len = rewrites.len();
 208         let (init, last) = rewrites.split_at_mut(len - (1 + trailing_try_num));
 209         fits_single_line = init.iter().all(|s| !s.contains('\n'));
 210
 211         if fits_single_line {
 212             fits_single_line = match expr.node {
 213                 ref e @ ast::ExprKind::MethodCall(..) => {
 214                     if rewrite_method_call_with_overflow(e,
 215                                                          &mut last[0],
 216                                                          almost_total,
 217                                                          total_span,
 218                                                          context,
 219                                                          shape) {
 220                         // If the first line of the last method does not fit into a single line
 221                         // after the others, allow new lines.
 222                         almost_total + first_line_width(&last[0]) < context.config.max_width()
 223                     } else {
 224                         false
 225                     }
 226                 }
 227                 _ => !last[0].contains('\n'),
 228             }
 229         }
 230     }
 231
 232     // Try overflowing the last element if we are using block indent.
 233     if !fits_single_line && context.config.fn_call_style() == IndentStyle::Block {
 234         let (init, last) = rewrites.split_at_mut(last_non_try_index);
 235         let almost_single_line = init.iter().all(|s| !s.contains('\n'));
 236         if almost_single_line {
 237             let overflow_shape = Shape {
 238                 width: one_line_budget,
 239                 ..parent_shape
 240             };
 241             fits_single_line = rewrite_last_child_with_overflow(context,
 242                                                                 &subexpr_list[trailing_try_num],
 243                                                                 overflow_shape,
 244                                                                 total_span,
 245                                                                 almost_total,
 246                                                                 one_line_budget,
 247                                                                 &mut last[0]);
 248         }
 249     }
 250
 251     let connector = if fits_single_line && !parent_rewrite_contains_newline {
 252         // Yay, we can put everything on one line.
 253         String::new()
 254     } else {
 255         // Use new lines.
 256         format!("\n{}", nested_shape.indent.to_string(context.config))
 257     };
 258
 259     let first_connector = if subexpr_list.is_empty() {
 260         ""
 261     } else if extend || first_subexpr_is_try {
 262         // 1 = ";", being conservative here.
 263         if last_line_width(&parent_rewrite) + first_line_width(&rewrites[0]) + 1 <=
 264            context.config.max_width() {
 265             ""
 266         } else {
 267             &*connector
 268         }
 269     } else {
 270         &*connector
 271     };
 272
 273     wrap_str(format!("{}{}{}",
 274                      parent_rewrite,
 275                      first_connector,
 276                      join_rewrites(&rewrites, &subexpr_list, &connector)),
 277              context.config.max_width(),
 278              shape)
 279 }
 280
 281 // True if the chain is only `?`s.
 282 fn chain_only_try(exprs: &[ast::Expr]) -> bool {
 283     exprs.iter().all(|e| if let ast::ExprKind::Try(_) = e.node {
 284                          true
 285                      } else {
 286                          false
 287                      })
 288 }
 289
 290 // Try to rewrite and replace the last non-try child. Return `true` if
 291 // replacing succeeds.
 292 fn rewrite_last_child_with_overflow(context: &RewriteContext,
 293                                     expr: &ast::Expr,
 294                                     shape: Shape,
 295                                     span: Span,
 296                                     almost_total: usize,
 297                                     one_line_budget: usize,
 298                                     last_child: &mut String)
 299                                     -> bool {
 300     if let Some(shape) = shape.shrink_left(almost_total) {
 301         if let Some(ref mut rw) = rewrite_chain_subexpr(expr, span, context, shape) {
 302             if almost_total + first_line_width(rw) <= one_line_budget {
 303                 ::std::mem::swap(last_child, rw);
 304                 return true;
 305             }
 306         }
 307     }
 308     false
 309 }
 310
 311 pub fn rewrite_try(expr: &ast::Expr,
 312                    try_count: usize,
 313                    context: &RewriteContext,
 314                    shape: Shape)
 315                    -> Option<String> {
 316     let sub_expr = try_opt!(expr.rewrite(context, try_opt!(shape.sub_width(try_count))));
 317     Some(format!("{}{}",
 318                  sub_expr,
 319                  iter::repeat("?").take(try_count).collect::<String>()))
 320 }
 321
 322 fn join_rewrites(rewrites: &[String], subexps: &[ast::Expr], connector: &str) -> String {
 323     let mut rewrite_iter = rewrites.iter();
 324     let mut result = rewrite_iter.next().unwrap().clone();
 325     let mut subexpr_iter = subexps.iter().rev();
 326     subexpr_iter.next();
 327
 328     for (rewrite, expr) in rewrite_iter.zip(subexpr_iter) {
 329         match expr.node {
 330             ast::ExprKind::Try(_) => (),
 331             _ => result.push_str(connector),
 332         };
 333         result.push_str(&rewrite[..]);
 334     }
 335
 336     result
 337 }
 338
 339 // States whether an expression's last line exclusively consists of closing
 340 // parens, braces, and brackets in its idiomatic formatting.
 341 fn is_block_expr(context: &RewriteContext, expr: &ast::Expr, repr: &str) -> bool {
 342     match expr.node {
 343         ast::ExprKind::Call(..) => {
 344             context.config.fn_call_style() == IndentStyle::Block && repr.contains('\n')
 345         }
 346         ast::ExprKind::Struct(..) |
 347         ast::ExprKind::While(..) |
 348         ast::ExprKind::WhileLet(..) |
 349         ast::ExprKind::If(..) |
 350         ast::ExprKind::IfLet(..) |
 351         ast::ExprKind::Block(..) |
 352         ast::ExprKind::Loop(..) |
 353         ast::ExprKind::ForLoop(..) |
 354         ast::ExprKind::Match(..) => repr.contains('\n'),
 355         ast::ExprKind::Paren(ref expr) |
 356         ast::ExprKind::Binary(_, _, ref expr) |
 357         ast::ExprKind::Index(_, ref expr) |
 358         ast::ExprKind::Unary(_, ref expr) => is_block_expr(context, expr, repr),
 359         _ => false,
 360     }
 361 }
 362
 363 // Returns the root of the chain and a Vec of the prefixes of the rest of the chain.
 364 // E.g., for input `a.b.c` we return (`a`, [`a.b.c`, `a.b`])
 365 fn make_subexpr_list(expr: &ast::Expr, context: &RewriteContext) -> (ast::Expr, Vec<ast::Expr>) {
 366     let mut subexpr_list = vec![expr.clone()];
 367
 368     while let Some(subexpr) = pop_expr_chain(subexpr_list.last().unwrap(), context) {
 369         subexpr_list.push(subexpr.clone());
 370     }
 371
 372     let parent = subexpr_list.pop().unwrap();
 373     (parent, subexpr_list)
 374 }
 375
 376 fn chain_indent(context: &RewriteContext, shape: Shape) -> Shape {
 377     match context.config.chain_indent() {
 378         IndentStyle::Visual => shape.visual_indent(0),
 379         IndentStyle::Block => shape.block_indent(context.config.tab_spaces()),
 380     }
 381 }
 382
 383 fn rewrite_method_call_with_overflow(expr_kind: &ast::ExprKind,
 384                                      last: &mut String,
 385                                      almost_total: usize,
 386                                      total_span: Span,
 387                                      context: &RewriteContext,
 388                                      shape: Shape)
 389                                      -> bool {
 390     if let &ast::ExprKind::MethodCall(ref method_name, ref types, ref expressions) = expr_kind {
 391         let shape = match shape.shrink_left(almost_total) {
 392             Some(b) => b,
 393             None => return false,
 394         };
 395         let mut last_rewrite = rewrite_method_call(method_name.node,
 396                                                    types,
 397                                                    expressions,
 398                                                    total_span,
 399                                                    context,
 400                                                    shape);
 401
 402         if let Some(ref mut s) = last_rewrite {
 403             ::std::mem::swap(s, last);
 404             true
 405         } else {
 406             false
 407         }
 408     } else {
 409         unreachable!();
 410     }
 411 }
 412
 413 // Returns the expression's subexpression, if it exists. When the subexpr
 414 // is a try! macro, we'll convert it to shorthand when the option is set.
 415 fn pop_expr_chain(expr: &ast::Expr, context: &RewriteContext) -> Option<ast::Expr> {
 416     match expr.node {
 417         ast::ExprKind::MethodCall(_, _, ref expressions) => {
 418             Some(convert_try(&expressions[0], context))
 419         }
 420         ast::ExprKind::TupField(ref subexpr, _) |
 421         ast::ExprKind::Field(ref subexpr, _) |
 422         ast::ExprKind::Try(ref subexpr) => Some(convert_try(subexpr, context)),
 423         _ => None,
 424     }
 425 }
 426
 427 fn convert_try(expr: &ast::Expr, context: &RewriteContext) -> ast::Expr {
 428     match expr.node {
 429         ast::ExprKind::Mac(ref mac) if context.config.use_try_shorthand() => {
 430             if let Some(subexpr) = convert_try_mac(mac, context) {
 431                 subexpr
 432             } else {
 433                 expr.clone()
 434             }
 435         }
 436         _ => expr.clone(),
 437     }
 438 }
 439
 440 // Rewrite the last element in the chain `expr`. E.g., given `a.b.c` we rewrite
 441 // `.c`.
 442 fn rewrite_chain_subexpr(expr: &ast::Expr,
 443                          span: Span,
 444                          context: &RewriteContext,
 445                          shape: Shape)
 446                          -> Option<String> {
 447     let rewrite_element = |expr_str: String| if expr_str.len() <= shape.width {
 448         Some(expr_str)
 449     } else {
 450         None
 451     };
 452
 453     match expr.node {
 454         ast::ExprKind::MethodCall(ref method_name, ref types, ref expressions) => {
 455             rewrite_method_call(method_name.node, types, expressions, span, context, shape)
 456         }
 457         ast::ExprKind::Field(_, ref field) => rewrite_element(format!(".{}", field.node)),
 458         ast::ExprKind::TupField(_, ref field) => rewrite_element(format!(".{}", field.node)),
 459         ast::ExprKind::Try(_) => rewrite_element(String::from("?")),
 460         _ => unreachable!(),
 461     }
 462 }
 463
 464 // Determines if we can continue formatting a given expression on the same line.
 465 fn is_continuable(expr: &ast::Expr) -> bool {
 466     match expr.node {
 467         ast::ExprKind::Path(..) => true,
 468         _ => false,
 469     }
 470 }
 471
 472 fn rewrite_method_call(method_name: ast::Ident,
 473                        types: &[ptr::P<ast::Ty>],
 474                        args: &[ptr::P<ast::Expr>],
 475                        span: Span,
 476                        context: &RewriteContext,
 477                        shape: Shape)
 478                        -> Option<String> {
 479     let (lo, type_str) = if types.is_empty() {
 480         (args[0].span.hi, String::new())
 481     } else {
 482         let type_list: Vec<_> =
 483             try_opt!(types.iter().map(|ty| ty.rewrite(context, shape)).collect());
 484
 485         let type_str = if context.config.spaces_within_angle_brackets() && type_list.len() > 0 {
 486             format!("::< {} >", type_list.join(", "))
 487         } else {
 488             format!("::<{}>", type_list.join(", "))
 489         };
 490
 491         (types.last().unwrap().span.hi, type_str)
 492     };
 493
 494     let callee_str = format!(".{}{}", method_name, type_str);
 495     let span = mk_sp(lo, span.hi);
 496
 497     rewrite_call(context, &callee_str, &args[1..], span, shape)
 498 }