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