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
  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_block_indent = match context.config.chain_base_indent {
  45         BlockIndentStyle::Visual => offset,
  46         BlockIndentStyle::Inherit => context.block_indent,
  47         BlockIndentStyle::Tabbed => context.block_indent.block_indent(context.config),
  48     };
  49     let parent_context = &RewriteContext { block_indent: parent_block_indent, ..*context };
  50     let parent = subexpr_list.pop().unwrap();
  51     let parent_rewrite = try_opt!(expr.rewrite(parent_context, width, offset));
  52     let (indent, extend) = if !parent_rewrite.contains('\n') && is_continuable(parent) ||
  53                               parent_rewrite.len() <= context.config.tab_spaces {
  54         (offset + Indent::new(0, parent_rewrite.len()), true)
  55     } else if is_block_expr(parent, &parent_rewrite) {
  56         (parent_block_indent, false)
  57     } else {
  58         match context.config.chain_indent {
  59             BlockIndentStyle::Inherit => (context.block_indent, false),
  60             BlockIndentStyle::Tabbed => (context.block_indent.block_indent(context.config), false),
  61             BlockIndentStyle::Visual => (offset + Indent::new(context.config.tab_spaces, 0), false),
  62         }
  63     };
  64
  65     let max_width = try_opt!((width + offset.width()).checked_sub(indent.width()));
  66     let mut rewrites = try_opt!(subexpr_list.iter()
  67                                             .rev()
  68                                             .map(|e| {
  69                                                 rewrite_chain_expr(e,
  70                                                                    total_span,
  71                                                                    context,
  72                                                                    max_width,
  73                                                                    indent)
  74                                             })
  75                                             .collect::<Option<Vec<_>>>());
  76
  77     // Total of all items excluding the last.
  78     let almost_total = rewrites[..rewrites.len() - 1]
  79                            .iter()
  80                            .fold(0, |a, b| a + first_line_width(b)) +
  81                        parent_rewrite.len();
  82     let total_width = almost_total + first_line_width(rewrites.last().unwrap());
  83     let veto_single_line = if context.config.take_source_hints && subexpr_list.len() > 1 {
  84         // Look at the source code. Unless all chain elements start on the same
  85         // line, we won't consider putting them on a single line either.
  86         let last_span = context.snippet(mk_sp(subexpr_list[1].span.hi, total_span.hi));
  87         let first_span = context.snippet(subexpr_list[1].span);
  88         let last_iter = last_span.chars().take_while(|c| c.is_whitespace());
  89
  90         first_span.chars().chain(last_iter).any(|c| c == '\n')
  91     } else {
  92         false
  93     };
  94
  95     let fits_single_line = !veto_single_line &&
  96                            match subexpr_list[0].node {
  97         ast::ExprKind::MethodCall(ref method_name, ref types, ref expressions)
  98             if context.config.chains_overflow_last => {
  99             let len = rewrites.len();
 100             let (init, last) = rewrites.split_at_mut(len - 1);
 101             let last = &mut last[0];
 102
 103             if init.iter().all(|s| !s.contains('\n')) && total_width <= width {
 104                 let last_rewrite = width.checked_sub(almost_total)
 105                                         .and_then(|inner_width| {
 106                                             rewrite_method_call(method_name.node,
 107                                                                 types,
 108                                                                 expressions,
 109                                                                 total_span,
 110                                                                 context,
 111                                                                 inner_width,
 112                                                                 offset + almost_total)
 113                                         });
 114                 match last_rewrite {
 115                     Some(mut string) => {
 116                         ::std::mem::swap(&mut string, last);
 117                         true
 118                     }
 119                     None => false,
 120                 }
 121             } else {
 122                 false
 123             }
 124         }
 125         _ => total_width <= width && rewrites.iter().all(|s| !s.contains('\n')),
 126     };
 127
 128     let connector = if fits_single_line && !parent_rewrite.contains('\n') {
 129         String::new()
 130     } else {
 131         format!("\n{}", indent.to_string(context.config))
 132     };
 133
 134     let first_connector = if extend {
 135         ""
 136     } else {
 137         &connector[..]
 138     };
 139
 140     wrap_str(format!("{}{}{}",
 141                      parent_rewrite,
 142                      first_connector,
 143                      rewrites.join(&connector)),
 144              context.config.max_width,
 145              width,
 146              offset)
 147 }
 148
 149 // States whether an expression's last line exclusively consists of closing
 150 // parens, braces and brackets in its idiomatic formatting.
 151 fn is_block_expr(expr: &ast::Expr, repr: &str) -> bool {
 152     match expr.node {
 153         ast::ExprKind::Struct(..) |
 154         ast::ExprKind::While(..) |
 155         ast::ExprKind::WhileLet(..) |
 156         ast::ExprKind::If(..) |
 157         ast::ExprKind::IfLet(..) |
 158         ast::ExprKind::Block(..) |
 159         ast::ExprKind::Loop(..) |
 160         ast::ExprKind::ForLoop(..) |
 161         ast::ExprKind::Match(..) => repr.contains('\n'),
 162         ast::ExprKind::Paren(ref expr) |
 163         ast::ExprKind::Binary(_, _, ref expr) |
 164         ast::ExprKind::Index(_, ref expr) |
 165         ast::ExprKind::Unary(_, ref expr) => is_block_expr(expr, repr),
 166         _ => false,
 167     }
 168 }
 169
 170 fn pop_expr_chain(expr: &ast::Expr) -> Option<&ast::Expr> {
 171     match expr.node {
 172         ast::ExprKind::MethodCall(_, _, ref expressions) => Some(&expressions[0]),
 173         ast::ExprKind::TupField(ref subexpr, _) |
 174         ast::ExprKind::Field(ref subexpr, _) => Some(subexpr),
 175         _ => None,
 176     }
 177 }
 178
 179 fn rewrite_chain_expr(expr: &ast::Expr,
 180                       span: Span,
 181                       context: &RewriteContext,
 182                       width: usize,
 183                       offset: Indent)
 184                       -> Option<String> {
 185     match expr.node {
 186         ast::ExprKind::MethodCall(ref method_name, ref types, ref expressions) => {
 187             let inner = &RewriteContext { block_indent: offset, ..*context };
 188             rewrite_method_call(method_name.node,
 189                                 types,
 190                                 expressions,
 191                                 span,
 192                                 inner,
 193                                 width,
 194                                 offset)
 195         }
 196         ast::ExprKind::Field(_, ref field) => {
 197             let s = format!(".{}", field.node);
 198             if s.len() <= width {
 199                 Some(s)
 200             } else {
 201                 None
 202             }
 203         }
 204         ast::ExprKind::TupField(_, ref field) => {
 205             let s = format!(".{}", field.node);
 206             if s.len() <= width {
 207                 Some(s)
 208             } else {
 209                 None
 210             }
 211         }
 212         _ => unreachable!(),
 213     }
 214 }
 215
 216 // Determines we can continue formatting a given expression on the same line.
 217 fn is_continuable(expr: &ast::Expr) -> bool {
 218     match expr.node {
 219         ast::ExprKind::Path(..) => true,
 220         _ => false,
 221     }
 222 }
 223
 224 fn rewrite_method_call(method_name: ast::Ident,
 225                        types: &[ptr::P<ast::Ty>],
 226                        args: &[ptr::P<ast::Expr>],
 227                        span: Span,
 228                        context: &RewriteContext,
 229                        width: usize,
 230                        offset: Indent)
 231                        -> Option<String> {
 232     let (lo, type_str) = if types.is_empty() {
 233         (args[0].span.hi, String::new())
 234     } else {
 235         let type_list: Vec<_> = try_opt!(types.iter()
 236                                               .map(|ty| ty.rewrite(context, width, offset))
 237                                               .collect());
 238
 239         (types.last().unwrap().span.hi, 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 }