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 use config::BlockIndentStyle;
  27
  28 use syntax::{ast, ptr};
  29 use syntax::codemap::{mk_sp, Span};
  30 use syntax::print::pprust;
  31
  32 pub fn rewrite_chain(mut expr: &ast::Expr,
  33                      context: &RewriteContext,
  34                      width: usize,
  35                      offset: Indent)
  36                      -> Option<String> {
  37     let total_span = expr.span;
  38     let mut subexpr_list = vec![expr];
  39
  40     while let Some(subexpr) = pop_expr_chain(expr) {
  41         subexpr_list.push(subexpr);
  42         expr = subexpr;
  43     }
  44
  45     let parent_block_indent = match context.config.chain_base_indent {
  46         BlockIndentStyle::Visual => offset,
  47         BlockIndentStyle::Inherit => context.block_indent,
  48         BlockIndentStyle::Tabbed => context.block_indent.block_indent(context.config),
  49     };
  50     let parent_context = &RewriteContext { block_indent: parent_block_indent, ..*context };
  51     let parent = subexpr_list.pop().unwrap();
  52     let parent_rewrite = try_opt!(expr.rewrite(parent_context, width, offset));
  53     let (indent, extend) = if !parent_rewrite.contains('\n') && is_continuable(parent) ||
  54                               parent_rewrite.len() <= context.config.tab_spaces {
  55         (offset + Indent::new(0, parent_rewrite.len()), true)
  56     } else if is_block_expr(parent, &parent_rewrite) {
  57         (parent_block_indent, false)
  58     } else {
  59         match context.config.chain_indent {
  60             BlockIndentStyle::Inherit => (context.block_indent, false),
  61             BlockIndentStyle::Tabbed => {
  62                 (context.block_indent.block_indent(context.config), false)
  63             }
  64             BlockIndentStyle::Visual => {
  65                 (offset + Indent::new(context.config.tab_spaces, 0), false)
  66             }
  67         }
  68     };
  69
  70     let max_width = try_opt!((width + offset.width()).checked_sub(indent.width()));
  71     let mut rewrites = try_opt!(subexpr_list.iter()
  72                                             .rev()
  73                                             .map(|e| {
  74                                                 rewrite_chain_expr(e,
  75                                                                    total_span,
  76                                                                    context,
  77                                                                    max_width,
  78                                                                    indent)
  79                                             })
  80                                             .collect::<Option<Vec<_>>>());
  81
  82     // Total of all items excluding the last.
  83     let almost_total = rewrites[..rewrites.len() - 1]
  84                            .iter()
  85                            .fold(0, |a, b| a + first_line_width(b)) +
  86                        parent_rewrite.len();
  87     let total_width = almost_total + first_line_width(rewrites.last().unwrap());
  88     let veto_single_line = if context.config.take_source_hints && subexpr_list.len() > 1 {
  89         // Look at the source code. Unless all chain elements start on the same
  90         // line, we won't consider putting them on a single line either.
  91         let last_span = context.snippet(mk_sp(subexpr_list[1].span.hi, total_span.hi));
  92         let first_span = context.snippet(subexpr_list[1].span);
  93         let last_iter = last_span.chars().take_while(|c| c.is_whitespace());
  94
  95         first_span.chars().chain(last_iter).any(|c| c == '\n')
  96     } else {
  97         false
  98     };
  99
 100     let fits_single_line = !veto_single_line &&
 101                            match subexpr_list[0].node {
 102         ast::Expr_::ExprMethodCall(ref method_name, ref types, ref expressions)
 103             if context.config.chains_overflow_last => {
 104             let len = rewrites.len();
 105             let (init, last) = rewrites.split_at_mut(len - 1);
 106             let last = &mut last[0];
 107
 108             if init.iter().all(|s| !s.contains('\n')) && total_width <= width {
 109                 let last_rewrite = width.checked_sub(almost_total)
 110                                         .and_then(|inner_width| {
 111                                             rewrite_method_call(method_name.node,
 112                                                                 types,
 113                                                                 expressions,
 114                                                                 total_span,
 115                                                                 context,
 116                                                                 inner_width,
 117                                                                 offset + almost_total)
 118                                         });
 119                 match last_rewrite {
 120                     Some(mut string) => {
 121                         ::std::mem::swap(&mut string, last);
 122                         true
 123                     }
 124                     None => false,
 125                 }
 126             } else {
 127                 false
 128             }
 129         }
 130         _ => total_width <= width && rewrites.iter().all(|s| !s.contains('\n')),
 131     };
 132
 133     let connector = if fits_single_line && !parent_rewrite.contains('\n') {
 134         String::new()
 135     } else {
 136         format!("\n{}", indent.to_string(context.config))
 137     };
 138
 139     let first_connector = if extend {
 140         ""
 141     } else {
 142         &connector[..]
 143     };
 144
 145     Some(format!("{}{}{}",
 146                  parent_rewrite,
 147                  first_connector,
 148                  rewrites.join(&connector)))
 149 }
 150
 151 // States whether an expression's last line exclusively consists of closing
 152 // parens, braces and brackets in its idiomatic formatting.
 153 fn is_block_expr(expr: &ast::Expr, repr: &str) -> bool {
 154     match expr.node {
 155         ast::Expr_::ExprStruct(..) |
 156         ast::Expr_::ExprWhile(..) |
 157         ast::Expr_::ExprWhileLet(..) |
 158         ast::Expr_::ExprIf(..) |
 159         ast::Expr_::ExprIfLet(..) |
 160         ast::Expr_::ExprBlock(..) |
 161         ast::Expr_::ExprLoop(..) |
 162         ast::Expr_::ExprForLoop(..) |
 163         ast::Expr_::ExprMatch(..) => repr.contains('\n'),
 164         ast::Expr_::ExprParen(ref expr) |
 165         ast::Expr_::ExprBinary(_, _, ref expr) |
 166         ast::Expr_::ExprIndex(_, ref expr) |
 167         ast::Expr_::ExprUnary(_, ref expr) => is_block_expr(expr, repr),
 168         _ => false,
 169     }
 170 }
 171
 172 fn pop_expr_chain<'a>(expr: &'a ast::Expr) -> Option<&'a ast::Expr> {
 173     match expr.node {
 174         ast::Expr_::ExprMethodCall(_, _, ref expressions) => Some(&expressions[0]),
 175         ast::Expr_::ExprTupField(ref subexpr, _) |
 176         ast::Expr_::ExprField(ref subexpr, _) => Some(subexpr),
 177         _ => None,
 178     }
 179 }
 180
 181 fn rewrite_chain_expr(expr: &ast::Expr,
 182                       span: Span,
 183                       context: &RewriteContext,
 184                       width: usize,
 185                       offset: Indent)
 186                       -> Option<String> {
 187     match expr.node {
 188         ast::Expr_::ExprMethodCall(ref method_name, ref types, ref expressions) => {
 189             let inner = &RewriteContext { block_indent: offset, ..*context };
 190             rewrite_method_call(method_name.node,
 191                                 types,
 192                                 expressions,
 193                                 span,
 194                                 inner,
 195                                 width,
 196                                 offset)
 197         }
 198         ast::Expr_::ExprField(_, ref field) => Some(format!(".{}", field.node)),
 199         ast::Expr_::ExprTupField(_, ref field) => Some(format!(".{}", field.node)),
 200         _ => unreachable!(),
 201     }
 202 }
 203
 204 // Determines we can continue formatting a given expression on the same line.
 205 fn is_continuable(expr: &ast::Expr) -> bool {
 206     match expr.node {
 207         ast::Expr_::ExprPath(..) => true,
 208         _ => false,
 209     }
 210 }
 211
 212 fn rewrite_method_call(method_name: ast::Ident,
 213                        types: &[ptr::P<ast::Ty>],
 214                        args: &[ptr::P<ast::Expr>],
 215                        span: Span,
 216                        context: &RewriteContext,
 217                        width: usize,
 218                        offset: Indent)
 219                        -> Option<String> {
 220     let (lo, type_str) = if types.is_empty() {
 221         (args[0].span.hi, String::new())
 222     } else {
 223         let type_list = types.iter().map(|ty| pprust::ty_to_string(ty)).collect::<Vec<_>>();
 224
 225         (types.last().unwrap().span.hi,
 226          format!("::<{}>", type_list.join(", ")))
 227     };
 228
 229     let callee_str = format!(".{}{}", method_name, type_str);
 230     let span = mk_sp(lo, span.hi);
 231
 232     rewrite_call(context, &callee_str, &args[1..], span, width, offset)
 233 }