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 and method calls.
  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 use Indent;
  23 use rewrite::{Rewrite, RewriteContext};
  24 use utils::first_line_width;
  25 use expr::rewrite_call;
  26
  27 use syntax::{ast, ptr};
  28 use syntax::codemap::{mk_sp, Span};
  29 use syntax::print::pprust;
  30
  31 pub fn rewrite_chain(mut expr: &ast::Expr,
  32                      context: &RewriteContext,
  33                      width: usize,
  34                      offset: Indent)
  35                      -> Option<String> {
  36     let total_span = expr.span;
  37     let mut subexpr_list = vec![expr];
  38
  39     while let Some(subexpr) = pop_expr_chain(expr) {
  40         subexpr_list.push(subexpr);
  41         expr = subexpr;
  42     }
  43
  44     let parent = subexpr_list.pop().unwrap();
  45     let parent_rewrite = try_opt!(expr.rewrite(context, width, offset));
  46     let (extra_indent, extend) = if !parent_rewrite.contains('\n') && is_continuable(parent) ||
  47                                     parent_rewrite.len() <= context.config.tab_spaces {
  48         (Indent::new(0, parent_rewrite.len()), true)
  49     } else {
  50         (Indent::new(context.config.tab_spaces, 0), false)
  51     };
  52     let indent = offset + extra_indent;
  53
  54     let max_width = try_opt!(width.checked_sub(extra_indent.width()));
  55     let mut rewrites = try_opt!(subexpr_list.iter()
  56                                             .rev()
  57                                             .map(|e| {
  58                                                 rewrite_chain_expr(e,
  59                                                                    total_span,
  60                                                                    context,
  61                                                                    max_width,
  62                                                                    indent)
  63                                             })
  64                                             .collect::<Option<Vec<_>>>());
  65
  66     // Total of all items excluding the last.
  67     let almost_total = rewrites.split_last()
  68                                .unwrap()
  69                                .1
  70                                .iter()
  71                                .fold(0, |a, b| a + first_line_width(b)) +
  72                        parent_rewrite.len();
  73     let total_width = almost_total + first_line_width(rewrites.last().unwrap());
  74     let veto_single_line = if context.config.take_source_hints && subexpr_list.len() > 1 {
  75         // Look at the source code. Unless all chain elements start on the same
  76         // line, we won't consider putting them on a single line either.
  77         let first_line_no = context.codemap.lookup_char_pos(subexpr_list[0].span.lo).line;
  78
  79         subexpr_list[1..]
  80             .iter()
  81             .any(|ex| context.codemap.lookup_char_pos(ex.span.hi).line != first_line_no)
  82     } else {
  83         false
  84     };
  85
  86     let fits_single_line = !veto_single_line &&
  87                            match subexpr_list[0].node {
  88         ast::Expr_::ExprMethodCall(ref method_name, ref types, ref expressions)
  89             if context.config.chains_overflow_last => {
  90             let (last, init) = rewrites.split_last_mut().unwrap();
  91
  92             if init.iter().all(|s| !s.contains('\n')) && total_width <= width {
  93                 let last_rewrite = width.checked_sub(almost_total)
  94                                         .and_then(|inner_width| {
  95                                             rewrite_method_call(method_name.node,
  96                                                                 types,
  97                                                                 expressions,
  98                                                                 total_span,
  99                                                                 context,
 100                                                                 inner_width,
 101                                                                 offset + almost_total)
 102                                         });
 103                 match last_rewrite {
 104                     Some(mut string) => {
 105                         ::std::mem::swap(&mut string, last);
 106                         true
 107                     }
 108                     None => false,
 109                 }
 110             } else {
 111                 false
 112             }
 113         }
 114         _ => total_width <= width && rewrites.iter().all(|s| !s.contains('\n')),
 115     };
 116
 117     let connector = if fits_single_line {
 118         String::new()
 119     } else {
 120         format!("\n{}", indent.to_string(context.config))
 121     };
 122
 123     let first_connector = if extend {
 124         ""
 125     } else {
 126         &connector[..]
 127     };
 128
 129     Some(format!("{}{}{}",
 130                  parent_rewrite,
 131                  first_connector,
 132                  rewrites.join(&connector)))
 133 }
 134
 135 fn pop_expr_chain<'a>(expr: &'a ast::Expr) -> Option<&'a ast::Expr> {
 136     match expr.node {
 137         ast::Expr_::ExprMethodCall(_, _, ref expressions) => {
 138             Some(&expressions[0])
 139         }
 140         ast::Expr_::ExprTupField(ref subexpr, _) |
 141         ast::Expr_::ExprField(ref subexpr, _) => {
 142             Some(subexpr)
 143         }
 144         _ => None,
 145     }
 146 }
 147
 148 fn rewrite_chain_expr(expr: &ast::Expr,
 149                       span: Span,
 150                       context: &RewriteContext,
 151                       width: usize,
 152                       offset: Indent)
 153                       -> Option<String> {
 154     match expr.node {
 155         ast::Expr_::ExprMethodCall(ref method_name, ref types, ref expressions) => {
 156             let inner = &RewriteContext { block_indent: offset, ..*context };
 157             rewrite_method_call(method_name.node,
 158                                 types,
 159                                 expressions,
 160                                 span,
 161                                 inner,
 162                                 width,
 163                                 offset)
 164         }
 165         ast::Expr_::ExprField(_, ref field) => {
 166             Some(format!(".{}", field.node))
 167         }
 168         ast::Expr_::ExprTupField(_, ref field) => {
 169             Some(format!(".{}", field.node))
 170         }
 171         _ => unreachable!(),
 172     }
 173 }
 174
 175 // Determines we can continue formatting a given expression on the same line.
 176 fn is_continuable(expr: &ast::Expr) -> bool {
 177     match expr.node {
 178         ast::Expr_::ExprPath(..) => true,
 179         _ => false,
 180     }
 181 }
 182
 183 fn rewrite_method_call(method_name: ast::Ident,
 184                        types: &[ptr::P<ast::Ty>],
 185                        args: &[ptr::P<ast::Expr>],
 186                        span: Span,
 187                        context: &RewriteContext,
 188                        width: usize,
 189                        offset: Indent)
 190                        -> Option<String> {
 191     let type_str = if types.is_empty() {
 192         String::new()
 193     } else {
 194         let type_list = types.iter().map(|ty| pprust::ty_to_string(ty)).collect::<Vec<_>>();
 195         format!("::<{}>", type_list.join(", "))
 196     };
 197
 198     let callee_str = format!(".{}{}", method_name, type_str);
 199     let span = mk_sp(args[0].span.hi, span.hi);
 200
 201     rewrite_call(context, &callee_str, &args[1..], span, width, offset)
 202 }