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         (offset + Indent::new(context.config.tab_spaces, 0), false)
  60     };
  61
  62     let max_width = try_opt!((width + offset.width()).checked_sub(indent.width()));
  63     let mut rewrites = try_opt!(subexpr_list.iter()
  64                                             .rev()
  65                                             .map(|e| {
  66                                                 rewrite_chain_expr(e,
  67                                                                    total_span,
  68                                                                    context,
  69                                                                    max_width,
  70                                                                    indent)
  71                                             })
  72                                             .collect::<Option<Vec<_>>>());
  73
  74     // Total of all items excluding the last.
  75     let almost_total = rewrites[..rewrites.len() - 1]
  76                            .iter()
  77                            .fold(0, |a, b| a + first_line_width(b)) +
  78                        parent_rewrite.len();
  79     let total_width = almost_total + first_line_width(rewrites.last().unwrap());
  80     let veto_single_line = if context.config.take_source_hints && subexpr_list.len() > 1 {
  81         // Look at the source code. Unless all chain elements start on the same
  82         // line, we won't consider putting them on a single line either.
  83         let first_line_no = context.codemap.lookup_char_pos(subexpr_list[0].span.lo).line;
  84
  85         subexpr_list[1..]
  86             .iter()
  87             .any(|ex| context.codemap.lookup_char_pos(ex.span.hi).line != first_line_no)
  88     } else {
  89         false
  90     };
  91
  92     let fits_single_line = !veto_single_line &&
  93                            match subexpr_list[0].node {
  94         ast::Expr_::ExprMethodCall(ref method_name, ref types, ref expressions)
  95             if context.config.chains_overflow_last => {
  96             let len = rewrites.len();
  97             let (init, last) = rewrites.split_at_mut(len - 1);
  98             let last = &mut last[0];
  99
 100             if init.iter().all(|s| !s.contains('\n')) && total_width <= width {
 101                 let last_rewrite = width.checked_sub(almost_total)
 102                                         .and_then(|inner_width| {
 103                                             rewrite_method_call(method_name.node,
 104                                                                 types,
 105                                                                 expressions,
 106                                                                 total_span,
 107                                                                 context,
 108                                                                 inner_width,
 109                                                                 offset + almost_total)
 110                                         });
 111                 match last_rewrite {
 112                     Some(mut string) => {
 113                         ::std::mem::swap(&mut string, last);
 114                         true
 115                     }
 116                     None => false,
 117                 }
 118             } else {
 119                 false
 120             }
 121         }
 122         _ => total_width <= width && rewrites.iter().all(|s| !s.contains('\n')),
 123     };
 124
 125     let connector = if fits_single_line && !parent_rewrite.contains('\n') {
 126         String::new()
 127     } else {
 128         format!("\n{}", indent.to_string(context.config))
 129     };
 130
 131     let first_connector = if extend {
 132         ""
 133     } else {
 134         &connector[..]
 135     };
 136
 137     Some(format!("{}{}{}",
 138                  parent_rewrite,
 139                  first_connector,
 140                  rewrites.join(&connector)))
 141 }
 142
 143 // States whether an expression's last line exclusively consists of closing
 144 // parens, braces and brackets in its idiomatic formatting.
 145 fn is_block_expr(expr: &ast::Expr, repr: &str) -> bool {
 146     match expr.node {
 147         ast::Expr_::ExprStruct(..) |
 148         ast::Expr_::ExprWhile(..) |
 149         ast::Expr_::ExprWhileLet(..) |
 150         ast::Expr_::ExprIf(..) |
 151         ast::Expr_::ExprIfLet(..) |
 152         ast::Expr_::ExprBlock(..) |
 153         ast::Expr_::ExprLoop(..) |
 154         ast::Expr_::ExprForLoop(..) |
 155         ast::Expr_::ExprMatch(..) => repr.contains('\n'),
 156         ast::Expr_::ExprParen(ref expr) |
 157         ast::Expr_::ExprBinary(_, _, ref expr) |
 158         ast::Expr_::ExprIndex(_, ref expr) |
 159         ast::Expr_::ExprUnary(_, ref expr) => is_block_expr(expr, repr),
 160         _ => false,
 161     }
 162 }
 163
 164 fn pop_expr_chain<'a>(expr: &'a ast::Expr) -> Option<&'a ast::Expr> {
 165     match expr.node {
 166         ast::Expr_::ExprMethodCall(_, _, ref expressions) => {
 167             Some(&expressions[0])
 168         }
 169         ast::Expr_::ExprTupField(ref subexpr, _) |
 170         ast::Expr_::ExprField(ref subexpr, _) => {
 171             Some(subexpr)
 172         }
 173         _ => None,
 174     }
 175 }
 176
 177 fn rewrite_chain_expr(expr: &ast::Expr,
 178                       span: Span,
 179                       context: &RewriteContext,
 180                       width: usize,
 181                       offset: Indent)
 182                       -> Option<String> {
 183     match expr.node {
 184         ast::Expr_::ExprMethodCall(ref method_name, ref types, ref expressions) => {
 185             let inner = &RewriteContext { block_indent: offset, ..*context };
 186             rewrite_method_call(method_name.node,
 187                                 types,
 188                                 expressions,
 189                                 span,
 190                                 inner,
 191                                 width,
 192                                 offset)
 193         }
 194         ast::Expr_::ExprField(_, ref field) => {
 195             Some(format!(".{}", field.node))
 196         }
 197         ast::Expr_::ExprTupField(_, ref field) => {
 198             Some(format!(".{}", field.node))
 199         }
 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 type_str = if types.is_empty() {
 221         String::new()
 222     } else {
 223         let type_list = types.iter().map(|ty| pprust::ty_to_string(ty)).collect::<Vec<_>>();
 224         format!("::<{}>", type_list.join(", "))
 225     };
 226
 227     let callee_str = format!(".{}{}", method_name, type_str);
 228     let span = mk_sp(args[0].span.hi, span.hi);
 229
 230     rewrite_call(context, &callee_str, &args[1..], span, width, offset)
 231 }