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::{wrap_str, 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 => (context.block_indent.block_indent(context.config), false),
  62             BlockIndentStyle::Visual => (offset + Indent::new(context.config.tab_spaces, 0), false),
  63         }
  64     };
  65
  66     let max_width = try_opt!((width + offset.width()).checked_sub(indent.width()));
  67     let mut rewrites = try_opt!(subexpr_list.iter()
  68                                             .rev()
  69                                             .map(|e| {
  70                                                 rewrite_chain_expr(e,
  71                                                                    total_span,
  72                                                                    context,
  73                                                                    max_width,
  74                                                                    indent)
  75                                             })
  76                                             .collect::<Option<Vec<_>>>());
  77
  78     // Total of all items excluding the last.
  79     let almost_total = rewrites[..rewrites.len() - 1]
  80                            .iter()
  81                            .fold(0, |a, b| a + first_line_width(b)) +
  82                        parent_rewrite.len();
  83     let total_width = almost_total + first_line_width(rewrites.last().unwrap());
  84     let veto_single_line = if context.config.take_source_hints && subexpr_list.len() > 1 {
  85         // Look at the source code. Unless all chain elements start on the same
  86         // line, we won't consider putting them on a single line either.
  87         let last_span = context.snippet(mk_sp(subexpr_list[1].span.hi, total_span.hi));
  88         let first_span = context.snippet(subexpr_list[1].span);
  89         let last_iter = last_span.chars().take_while(|c| c.is_whitespace());
  90
  91         first_span.chars().chain(last_iter).any(|c| c == '\n')
  92     } else {
  93         false
  94     };
  95
  96     let fits_single_line = !veto_single_line &&
  97                            match subexpr_list[0].node {
  98         ast::Expr_::ExprMethodCall(ref method_name, ref types, ref expressions)
  99             if context.config.chains_overflow_last => {
 100             let len = rewrites.len();
 101             let (init, last) = rewrites.split_at_mut(len - 1);
 102             let last = &mut last[0];
 103
 104             if init.iter().all(|s| !s.contains('\n')) && total_width <= width {
 105                 let last_rewrite = width.checked_sub(almost_total)
 106                                         .and_then(|inner_width| {
 107                                             rewrite_method_call(method_name.node,
 108                                                                 types,
 109                                                                 expressions,
 110                                                                 total_span,
 111                                                                 context,
 112                                                                 inner_width,
 113                                                                 offset + almost_total)
 114                                         });
 115                 match last_rewrite {
 116                     Some(mut string) => {
 117                         ::std::mem::swap(&mut string, last);
 118                         true
 119                     }
 120                     None => false,
 121                 }
 122             } else {
 123                 false
 124             }
 125         }
 126         _ => total_width <= width && rewrites.iter().all(|s| !s.contains('\n')),
 127     };
 128
 129     let connector = if fits_single_line && !parent_rewrite.contains('\n') {
 130         String::new()
 131     } else {
 132         format!("\n{}", indent.to_string(context.config))
 133     };
 134
 135     let first_connector = if extend {
 136         ""
 137     } else {
 138         &connector[..]
 139     };
 140
 141     wrap_str(format!("{}{}{}",
 142                      parent_rewrite,
 143                      first_connector,
 144                      rewrites.join(&connector)),
 145              context.config.max_width,
 146              width,
 147              offset)
 148 }
 149
 150 // States whether an expression's last line exclusively consists of closing
 151 // parens, braces and brackets in its idiomatic formatting.
 152 fn is_block_expr(expr: &ast::Expr, repr: &str) -> bool {
 153     match expr.node {
 154         ast::Expr_::ExprStruct(..) |
 155         ast::Expr_::ExprWhile(..) |
 156         ast::Expr_::ExprWhileLet(..) |
 157         ast::Expr_::ExprIf(..) |
 158         ast::Expr_::ExprIfLet(..) |
 159         ast::Expr_::ExprBlock(..) |
 160         ast::Expr_::ExprLoop(..) |
 161         ast::Expr_::ExprForLoop(..) |
 162         ast::Expr_::ExprMatch(..) => repr.contains('\n'),
 163         ast::Expr_::ExprParen(ref expr) |
 164         ast::Expr_::ExprBinary(_, _, ref expr) |
 165         ast::Expr_::ExprIndex(_, ref expr) |
 166         ast::Expr_::ExprUnary(_, ref expr) => is_block_expr(expr, repr),
 167         _ => false,
 168     }
 169 }
 170
 171 fn pop_expr_chain(expr: &ast::Expr) -> Option<&ast::Expr> {
 172     match expr.node {
 173         ast::Expr_::ExprMethodCall(_, _, ref expressions) => Some(&expressions[0]),
 174         ast::Expr_::ExprTupField(ref subexpr, _) |
 175         ast::Expr_::ExprField(ref subexpr, _) => Some(subexpr),
 176         _ => None,
 177     }
 178 }
 179
 180 fn rewrite_chain_expr(expr: &ast::Expr,
 181                       span: Span,
 182                       context: &RewriteContext,
 183                       width: usize,
 184                       offset: Indent)
 185                       -> Option<String> {
 186     match expr.node {
 187         ast::Expr_::ExprMethodCall(ref method_name, ref types, ref expressions) => {
 188             let inner = &RewriteContext { block_indent: offset, ..*context };
 189             rewrite_method_call(method_name.node,
 190                                 types,
 191                                 expressions,
 192                                 span,
 193                                 inner,
 194                                 width,
 195                                 offset)
 196         }
 197         ast::Expr_::ExprField(_, ref field) => {
 198             let s = format!(".{}", field.node);
 199             if s.len() <= width {
 200                 Some(s)
 201             } else {
 202                 None
 203             }
 204         }
 205         ast::Expr_::ExprTupField(_, ref field) => {
 206             let s = format!(".{}", field.node);
 207             if s.len() <= width {
 208                 Some(s)
 209             } else {
 210                 None
 211             }
 212         }
 213         _ => unreachable!(),
 214     }
 215 }
 216
 217 // Determines we can continue formatting a given expression on the same line.
 218 fn is_continuable(expr: &ast::Expr) -> bool {
 219     match expr.node {
 220         ast::Expr_::ExprPath(..) => true,
 221         _ => false,
 222     }
 223 }
 224
 225 fn rewrite_method_call(method_name: ast::Ident,
 226                        types: &[ptr::P<ast::Ty>],
 227                        args: &[ptr::P<ast::Expr>],
 228                        span: Span,
 229                        context: &RewriteContext,
 230                        width: usize,
 231                        offset: Indent)
 232                        -> Option<String> {
 233     let (lo, type_str) = if types.is_empty() {
 234         (args[0].span.hi, String::new())
 235     } else {
 236         let type_list = types.iter().map(|ty| pprust::ty_to_string(ty)).collect::<Vec<_>>();
 237
 238         (types.last().unwrap().span.hi,
 239          format!("::<{}>", type_list.join(", ")))
 240     };
 241
 242     let callee_str = format!(".{}{}", method_name, type_str);
 243     let span = mk_sp(lo, span.hi);
 244
 245     rewrite_call(context, &callee_str, &args[1..], span, width, offset)
 246 }