path: root/src/items.rs

// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

// Formatting top-level items - functions, structs, enums, traits, impls.

use {ReturnIndent, BraceStyle};
use utils::{format_visibility, make_indent};
use lists::{write_list, ListFormatting, SeparatorTactic, ListTactic};
use visitor::FmtVisitor;
use syntax::{ast, abi};
use syntax::codemap::{self, Span, BytePos};
use syntax::print::pprust;
use syntax::parse::token;

impl<'a> FmtVisitor<'a> {
    pub fn rewrite_fn(&mut self,
                      indent: usize,
                      ident: ast::Ident,
                      fd: &ast::FnDecl,
                      explicit_self: Option<&ast::ExplicitSelf>,
                      generics: &ast::Generics,
                      unsafety: &ast::Unsafety,
                      constness: &ast::Constness,
                      abi: &abi::Abi,
                      vis: ast::Visibility,
                      span_end: BytePos)
        -> String
    {
        let newline_brace = self.newline_for_brace(&generics.where_clause);

        let mut result = self.rewrite_fn_base(indent,
                                              ident,
                                              fd,
                                              explicit_self,
                                              generics,
                                              unsafety,
                                              constness,
                                              abi,
                                              vis,
                                              span_end,
                                              newline_brace);

        // Prepare for the function body by possibly adding a newline and indent.
        // FIXME we'll miss anything between the end of the signature and the start
        // of the body, but we need more spans from the compiler to solve this.
        if newline_brace {
            result.push('\n');
            result.push_str(&make_indent(indent));
        } else {
            result.push(' ');
        }

        result
    }

    pub fn rewrite_required_fn(&mut self,
                               indent: usize,
                               ident: ast::Ident,
                               sig: &ast::MethodSig,
                               span: Span)
        -> String
    {
        // Drop semicolon or it will be interpreted as comment
        let span_end = span.hi - BytePos(1);

        let mut result = self.rewrite_fn_base(indent,
                                              ident,
                                              &sig.decl,
                                              Some(&sig.explicit_self),
                                              &sig.generics,
                                              &sig.unsafety,
                                              &sig.constness,
                                              &sig.abi,
                                              ast::Visibility::Inherited,
                                              span_end,
                                              false);

        // Re-attach semicolon
        result.push(';');

        result
    }

    fn rewrite_fn_base(&mut self,
                       indent: usize,
                       ident: ast::Ident,
                       fd: &ast::FnDecl,
                       explicit_self: Option<&ast::ExplicitSelf>,
                       generics: &ast::Generics,
                       unsafety: &ast::Unsafety,
                       constness: &ast::Constness,
                       abi: &abi::Abi,
                       vis: ast::Visibility,
                       span_end: BytePos,
                       newline_brace: bool)
        -> String
    {
        // FIXME we'll lose any comments in between parts of the function decl, but anyone
        // who comments there probably deserves what they get.

        let where_clause = &generics.where_clause;

        let mut result = String::with_capacity(1024);
        // Vis unsafety abi.
        result.push_str(format_visibility(vis));

        if let &ast::Unsafety::Unsafe = unsafety {
            result.push_str("unsafe ");
        }
        if let &ast::Constness::Const = constness {
            result.push_str("const ");
        }
        if *abi != abi::Rust {
            result.push_str("extern ");
            result.push_str(&abi.to_string());
            result.push(' ');
        }

        // fn foo
        result.push_str("fn ");
        result.push_str(&token::get_ident(ident));

        // Generics.
        let generics_indent = indent + result.len();
        result.push_str(&self.rewrite_generics(generics,
                                               generics_indent,
                                               span_for_return(&fd.output).lo));

        let ret_str = self.rewrite_return(&fd.output);

        // Args.
        let (one_line_budget, multi_line_budget, mut arg_indent) =
            self.compute_budgets_for_args(&result, indent, ret_str.len(), newline_brace);

        debug!("rewrite_fn: one_line_budget: {}, multi_line_budget: {}, arg_indent: {}",
               one_line_budget, multi_line_budget, arg_indent);

        // Check if vertical layout was forced by compute_budget_for_args.
        if one_line_budget <= 0 {
            if config!(fn_args_paren_newline) {
                result.push('\n');
                result.push_str(&make_indent(arg_indent));
                arg_indent = arg_indent + 1; // extra space for `(`
                result.push('(');
            } else {
                result.push_str("(\n");
                result.push_str(&make_indent(arg_indent));
            }
        } else {
            result.push('(');
        }

        result.push_str(&self.rewrite_args(&fd.inputs,
                                           explicit_self,
                                           one_line_budget,
                                           multi_line_budget,
                                           arg_indent,
                                           span_for_return(&fd.output)));
        result.push(')');

        // Return type.
        if ret_str.len() > 0 {
            // If we've already gone multi-line, or the return type would push
            // over the max width, then put the return type on a new line.
            if result.contains("\n") ||
               result.len() + indent + ret_str.len() > config!(max_width) {
                let indent = match config!(fn_return_indent) {
                    ReturnIndent::WithWhereClause => indent + 4,
                    // TODO we might want to check that using the arg indent doesn't
                    // blow our budget, and if it does, then fallback to the where
                    // clause indent.
                    _ => arg_indent,
                };

                result.push('\n');
                result.push_str(&make_indent(indent));
            } else {
                result.push(' ');
            }
            result.push_str(&ret_str);

            // Comment between return type and the end of the decl.
            let snippet_lo = fd.output.span().hi;
            if where_clause.predicates.len() == 0 {
                let snippet_hi = span_end;
                let snippet = self.snippet(codemap::mk_sp(snippet_lo, snippet_hi));
                let snippet = snippet.trim();
                if snippet.len() > 0 {
                    result.push(' ');
                    result.push_str(snippet);
                }
            } else {
                // FIXME it would be nice to catch comments between the return type
                // and the where clause, but we don't have a span for the where
                // clause.
            }
        }

        // Where clause.
        result.push_str(&self.rewrite_where_clause(where_clause, indent, span_end));

        result
    }

    fn rewrite_args(&self,
                    args: &[ast::Arg],
                    explicit_self: Option<&ast::ExplicitSelf>,
                    one_line_budget: usize,
                    multi_line_budget: usize,
                    arg_indent: usize,
                    ret_span: Span)
        -> String
    {
        let mut arg_item_strs: Vec<_> = args.iter().map(|a| self.rewrite_fn_input(a)).collect();
        // Account for sugary self.
        let mut min_args = 1;
        if let Some(explicit_self) = explicit_self {
            match explicit_self.node {
                ast::ExplicitSelf_::SelfRegion(ref lt, ref m, _) => {
                    let lt_str = match lt {
                        &Some(ref l) => format!("{} ", pprust::lifetime_to_string(l)),
                        &None => String::new(),
                    };
                    let mut_str = match m {
                        &ast::Mutability::MutMutable => "mut ".to_owned(),
                        &ast::Mutability::MutImmutable => String::new(),
                    };
                    arg_item_strs[0] = format!("&{}{}self", lt_str, mut_str);
                    min_args = 2;
                }
                ast::ExplicitSelf_::SelfExplicit(ref ty, _) => {
                    arg_item_strs[0] = format!("self: {}", pprust::ty_to_string(ty));
                }
                ast::ExplicitSelf_::SelfValue(_) => {
                    assert!(args.len() >= 1, "&[ast::Arg] shouldn't be empty.");

                    // this hacky solution caused by absence of `Mutability` in `SelfValue`.
                    let mut_str = {
                        if let ast::Pat_::PatIdent(ast::BindingMode::BindByValue(mutability), _, _)
                                = args[0].pat.node {
                            match mutability {
                                ast::Mutability::MutMutable => "mut ",
                                ast::Mutability::MutImmutable => "",
                            }
                        } else {
                            panic!("there is a bug or change in structure of AST, aborting.");
                        }
                    };

                    arg_item_strs[0] = format!("{}self", mut_str);
                    min_args = 2;
                }
                _ => {}
            }
        }

        // Comments between args
        let mut arg_comments = Vec::new();
        if min_args == 2 {
            arg_comments.push("".to_owned());
        }
        // TODO if there are no args, there might still be a comment, but without
        // spans for the comment or parens, there is no chance of getting it right.
        // You also don't get to put a comment on self, unless it is explicit.
        if args.len() >= min_args {
            arg_comments = self.make_comments_for_list(arg_comments,
                                                       args[min_args-1..].iter(),
                                                       ",",
                                                       ")",
                                                       |arg| arg.pat.span.lo,
                                                       |arg| arg.ty.span.hi,
                                                       ret_span.lo);
        }

        debug!("comments: {:?}", arg_comments);

        // If there are // comments, keep them multi-line.
        let mut list_tactic = ListTactic::HorizontalVertical;
        if arg_comments.iter().any(|c| c.contains("//")) {
            list_tactic = ListTactic::Vertical;
        }

        assert_eq!(arg_item_strs.len(), arg_comments.len());
        let arg_strs: Vec<_> = arg_item_strs.into_iter().zip(arg_comments.into_iter()).collect();

        let fmt = ListFormatting {
            tactic: list_tactic,
            separator: ",",
            trailing_separator: SeparatorTactic::Never,
            indent: arg_indent,
            h_width: one_line_budget,
            v_width: multi_line_budget,
        };

        write_list(&arg_strs, &fmt)
    }

    // Gets comments in between items of a list.
    fn make_comments_for_list<T, I, F1, F2>(&self,
                                            prefix: Vec<String>,
                                            mut it: I,
                                            separator: &str,
                                            terminator: &str,
                                            get_lo: F1,
                                            get_hi: F2,
                                            next_span_start: BytePos)
        -> Vec<String>
        where I: Iterator<Item=T>,
              F1: Fn(&T) -> BytePos,
              F2: Fn(&T) -> BytePos
    {
        let mut result = prefix;

        let mut prev_end = get_hi(&it.next().unwrap());
        for item in it {
            let cur_start = get_lo(&item);
            let snippet = self.snippet(codemap::mk_sp(prev_end, cur_start));
            let mut snippet = snippet.trim();
            let white_space: &[_] = &[' ', '\t'];
            if snippet.starts_with(separator) {
                snippet = snippet[separator.len()..].trim_matches(white_space);
            } else if snippet.ends_with(separator) {
                snippet = snippet[..snippet.len()-separator.len()].trim_matches(white_space);
            }
            result.push(snippet.to_owned());
            prev_end = get_hi(&item);
        }
        // Get the last commment.
        // FIXME If you thought the crap with the commas was ugly, just wait.
        // This is awful. We're going to look from the last item span to the
        // start of the return type span, then we drop everything after the
        // first closing paren. Obviously, this will break if there is a
        // closing paren in the comment.
        // The fix is comments in the AST or a span for the closing paren.
        let snippet = self.snippet(codemap::mk_sp(prev_end, next_span_start));
        let snippet = snippet.trim();
        let snippet = &snippet[..snippet.find(terminator).unwrap_or(snippet.len())];
        let snippet = snippet.trim();
        result.push(snippet.to_owned());

        result
    }

    fn compute_budgets_for_args(&self,
                                result: &str,
                                indent: usize,
                                ret_str_len: usize,
                                newline_brace: bool)
        -> (usize, usize, usize)
    {
        let mut budgets = None;

        // Try keeping everything on the same line
        if !result.contains("\n") {
            // 3 = `() `, space is before ret_string
            let mut used_space = indent + result.len() + ret_str_len + 3;
            if !newline_brace {
                used_space += 2;
            }
            let one_line_budget = if used_space > config!(max_width) {
                0
            } else {
                config!(max_width) - used_space
            };

            // 2 = `()`
            let used_space = indent + result.len() + 2;
            let max_space = config!(ideal_width) + config!(leeway);
            debug!("compute_budgets_for_args: used_space: {}, max_space: {}",
                   used_space, max_space);
            if used_space < max_space {
                budgets = Some((one_line_budget,
                                max_space - used_space,
                                indent + result.len() + 1));
            }
        }

        // Didn't work. we must force vertical layout and put args on a newline.
        if let None = budgets {
            let new_indent = indent + config!(tab_spaces);
            let used_space = new_indent + 2; // account for `(` and `)`
            let max_space = config!(ideal_width) + config!(leeway);
            if used_space > max_space {
                // Whoops! bankrupt.
                // TODO take evasive action, perhaps kill the indent or something.
            } else {
                budgets = Some((0, max_space - used_space, new_indent));
            }
        }

        budgets.unwrap()
    }

    fn newline_for_brace(&self, where_clause: &ast::WhereClause) -> bool {
        match config!(fn_brace_style) {
            BraceStyle::AlwaysNextLine => true,
            BraceStyle::SameLineWhere if where_clause.predicates.len() > 0 => true,
            _ => false,
        }
    }

    pub fn visit_enum(&mut self,
                      ident: ast::Ident,
                      vis: ast::Visibility,
                      enum_def: &ast::EnumDef,
                      generics: &ast::Generics,
                      span: Span)
    {
        let header_str = self.format_header("enum", ident, vis);
        self.changes.push_str_span(span, &header_str);

        let enum_snippet = self.snippet(span);
        // FIXME this will give incorrect results if there is a { in a comment.
        let body_start = span.lo + BytePos(enum_snippet.find('{').unwrap() as u32 + 1);
        let generics_str = self.format_generics(generics, body_start);
        self.changes.push_str_span(span, &generics_str);

        self.last_pos = body_start;
        self.block_indent += config!(tab_spaces);
        for (i, f) in enum_def.variants.iter().enumerate() {
            let next_span_start: BytePos = if i == enum_def.variants.len() - 1 {
                span.hi
            } else {
                enum_def.variants[i + 1].span.lo
            };

            self.visit_variant(f, i == enum_def.variants.len() - 1, next_span_start);
        }
        self.block_indent -= config!(tab_spaces);

        self.format_missing_with_indent(span.lo + BytePos(enum_snippet.rfind('}').unwrap() as u32));
        self.changes.push_str_span(span, "}");
    }

    // Variant of an enum
    fn visit_variant(&mut self,
                     field: &ast::Variant,
                     last_field: bool,
                     next_span_start: BytePos)
    {
        if self.visit_attrs(&field.node.attrs) {
            return;
        }

        if let ast::VariantKind::TupleVariantKind(ref types) = field.node.kind {
            self.format_missing_with_indent(field.span.lo);

            let vis = format_visibility(field.node.vis);
            self.changes.push_str_span(field.span, vis);
            let name = field.node.name.to_string();
            self.changes.push_str_span(field.span, &name);

            let mut result = String::new();

            if types.len() > 0 {
                let comments = self.make_comments_for_list(Vec::new(),
                                                           types.iter().map(|arg| arg.ty.span),
                                                           ",",
                                                           ")",
                                                           |span| span.lo,
                                                           |span| span.hi,
                                                           next_span_start);

                let type_strings: Vec<_> = types.iter()
                                                .map(|arg| pprust::ty_to_string(&arg.ty))
                                                .zip(comments.into_iter())
                                                .collect();

                result.push('(');

                let indent = self.block_indent
                             + vis.len()
                             + field.node.name.to_string().len()
                             + 1; // 1 = (

                let comma_cost = if config!(enum_trailing_comma) { 1 } else { 0 };
                let budget = config!(ideal_width) - indent - comma_cost - 1; // 1 = )

                let fmt = ListFormatting {
                    tactic: ListTactic::HorizontalVertical,
                    separator: ",",
                    trailing_separator: SeparatorTactic::Never,
                    indent: indent,
                    h_width: budget,
                    v_width: budget,
                };
                result.push_str(&write_list(&type_strings, &fmt));
                result.push(')');
            }

            if let Some(ref expr) = field.node.disr_expr {
                result.push_str(" = ");
                let expr_snippet = self.snippet(expr.span);
                result.push_str(&expr_snippet);

                // Make sure we do not exceed column limit
                // 4 = " = ,"
                assert!(config!(max_width) >= vis.len() + name.len() + expr_snippet.len() + 4,
                        "Enum variant exceeded column limit");
            }

            self.changes.push_str_span(field.span, &result);

            if !last_field || config!(enum_trailing_comma) {
                self.changes.push_str_span(field.span, ",");
            }
        }

        // TODO: deal with struct-like variants

        self.last_pos = field.span.hi + BytePos(1);
    }

    pub fn visit_struct(&mut self,
                        ident: ast::Ident,
                        vis: ast::Visibility,
                        struct_def: &ast::StructDef,
                        generics: &ast::Generics,
                        span: Span)
    {
        let header_str = self.format_header("struct", ident, vis);
        self.changes.push_str_span(span, &header_str);

        if struct_def.fields.len() == 0 {
            assert!(generics.where_clause.predicates.len() == 0,
                    "No-field struct with where clause?");
            assert!(generics.lifetimes.len() == 0, "No-field struct with generics?");
            assert!(generics.ty_params.len() == 0, "No-field struct with generics?");

            self.changes.push_str_span(span, ";");
            return;
        }

        let generics_str = self.format_generics(generics, struct_def.fields[0].span.lo);
        self.changes.push_str_span(span, &generics_str);

        let struct_snippet = self.snippet(span);
        // FIXME this will give incorrect results if there is a { in a comment.
        self.last_pos = span.lo + BytePos(struct_snippet.find('{').unwrap() as u32 + 1);

        self.block_indent += config!(tab_spaces);
        for (i, f) in struct_def.fields.iter().enumerate() {
            self.visit_field(f, i == struct_def.fields.len() - 1, span.lo, &struct_snippet);
        }
        self.block_indent -= config!(tab_spaces);

        self.format_missing_with_indent(span.lo + BytePos(struct_snippet.rfind('}').unwrap() as u32));
        self.changes.push_str_span(span, "}");
    }

    fn format_header(&self,
                     item_name: &str,
                     ident: ast::Ident,
                     vis: ast::Visibility)
        -> String
    {
        format!("{}{} {}", format_visibility(vis), item_name, &token::get_ident(ident))
    }

    fn format_generics(&self,
                       generics: &ast::Generics,
                       span_end: BytePos)
        -> String
    {
        let mut result = self.rewrite_generics(generics, self.block_indent, span_end);

        if generics.where_clause.predicates.len() > 0 {
            result.push_str(&self.rewrite_where_clause(&generics.where_clause,
                                                             self.block_indent,
                                                             span_end));
            result.push_str(&make_indent(self.block_indent));
            result.push_str("\n{");

        } else {
            result.push_str(" {");
        }

        result
    }

    // Field of a struct
    fn visit_field(&mut self,
                   field: &ast::StructField,
                   last_field: bool,
                   // These two args are for missing spans hacks.
                   struct_start: BytePos,
                   struct_snippet: &str)
    {
        if self.visit_attrs(&field.node.attrs) {
            return;
        }
        self.format_missing_with_indent(field.span.lo);

        let name = match field.node.kind {
            ast::StructFieldKind::NamedField(ident, _) => Some(token::get_ident(ident)),
            ast::StructFieldKind::UnnamedField(_) => None,
        };
        let vis = match field.node.kind {
            ast::StructFieldKind::NamedField(_, vis) |
            ast::StructFieldKind::UnnamedField(vis) => format_visibility(vis)
        };
        let typ = pprust::ty_to_string(&field.node.ty);

        let mut field_str = match name {
            Some(name) => {
                let budget = config!(ideal_width) - self.block_indent;
                // 3 is being conservative and assuming that there will be a trailing comma.
                if self.block_indent + vis.len() + name.len() + typ.len() + 3 > budget {
                    format!("{}{}:\n{}{}",
                            vis,
                            name,
                            &make_indent(self.block_indent + config!(tab_spaces)),
                            typ)
                } else {
                    format!("{}{}: {}", vis, name, typ)
                }
            }
            None => format!("{}{}", vis, typ),
        };
        if !last_field || config!(struct_trailing_comma) {
            field_str.push(',');
        }
        self.changes.push_str_span(field.span, &field_str);

        // This hack makes sure we only add comments etc. after the comma, and
        // makes sure we don't repeat any commas.
        let hi = field.span.hi;
        // FIXME a comma in a comment will break this hack.
        let comma_pos = match struct_snippet[(hi.0 - struct_start.0) as usize..].find(',') {
            Some(i) => i,
            None => 0,
        };
        self.last_pos = hi + BytePos(comma_pos as u32 + 1);
    }

    fn rewrite_generics(&self, generics: &ast::Generics, indent: usize, span_end: BytePos) -> String {
        // FIXME convert bounds to where clauses where they get too big or if
        // there is a where clause at all.
        let mut result = String::new();
        let lifetimes: &[_] = &generics.lifetimes;
        let tys: &[_] = &generics.ty_params;
        if lifetimes.len() + tys.len() == 0 {
            return result;
        }

        let budget = config!(max_width) - indent - 2;
        // TODO might need to insert a newline if the generics are really long
        result.push('<');

        // Strings for the generics.
        let lt_strs = lifetimes.iter().map(|l| self.rewrite_lifetime_def(l));
        let ty_strs = tys.iter().map(|ty| self.rewrite_ty_param(ty));

        // Extract comments between generics.
        let lt_spans = lifetimes.iter().map(|l| {
            let hi = if l.bounds.len() == 0 {
                l.lifetime.span.hi
            } else {
                l.bounds[l.bounds.len() - 1].span.hi
            };
            codemap::mk_sp(l.lifetime.span.lo, hi)
        });
        let ty_spans = tys.iter().map(span_for_ty_param);
        let comments = self.make_comments_for_list(Vec::new(),
                                                   lt_spans.chain(ty_spans),
                                                   ",",
                                                   ">",
                                                   |sp| sp.lo,
                                                   |sp| sp.hi,
                                                   span_end);

        // If there are // comments, keep them multi-line.
        let mut list_tactic = ListTactic::HorizontalVertical;
        if comments.iter().any(|c| c.contains("//")) {
            list_tactic = ListTactic::Vertical;
        }

        let generics_strs: Vec<_> = lt_strs.chain(ty_strs).zip(comments.into_iter()).collect();
        let fmt = ListFormatting {
            tactic: list_tactic,
            separator: ",",
            trailing_separator: SeparatorTactic::Never,
            indent: indent + 1,
            h_width: budget,
            v_width: budget,
        };
        result.push_str(&write_list(&generics_strs, &fmt));

        result.push('>');

        result
    }

    fn rewrite_where_clause(&self,
                            where_clause: &ast::WhereClause,
                            indent: usize,
                            span_end: BytePos)
        -> String
    {
        let mut result = String::new();
        if where_clause.predicates.len() == 0 {
            return result;
        }

        result.push('\n');
        result.push_str(&make_indent(indent + 4));
        result.push_str("where ");

        let comments = self.make_comments_for_list(Vec::new(),
                                                   where_clause.predicates.iter(),
                                                   ",",
                                                   "{",
                                                   |pred| span_for_where_pred(pred).lo,
                                                   |pred| span_for_where_pred(pred).hi,
                                                   span_end);

        let where_strs: Vec<_> = where_clause.predicates.iter()
                                                        .map(|p| (self.rewrite_pred(p)))
                                                        .zip(comments.into_iter())
                                                        .collect();

        let budget = config!(ideal_width) + config!(leeway) - indent - 10;
        let fmt = ListFormatting {
            tactic: ListTactic::Vertical,
            separator: ",",
            trailing_separator: SeparatorTactic::Never,
            indent: indent + 10,
            h_width: budget,
            v_width: budget,
        };
        result.push_str(&write_list(&where_strs, &fmt));

        result
    }

    fn rewrite_return(&self, ret: &ast::FunctionRetTy) -> String {
        match *ret {
            ast::FunctionRetTy::DefaultReturn(_) => String::new(),
            ast::FunctionRetTy::NoReturn(_) => "-> !".to_owned(),
            ast::FunctionRetTy::Return(ref ty) => "-> ".to_owned() + &pprust::ty_to_string(ty),
        }
    }

    // TODO we farm this out, but this could spill over the column limit, so we ought to handle it properly
    fn rewrite_fn_input(&self, arg: &ast::Arg) -> String {
        format!("{}: {}",
                pprust::pat_to_string(&arg.pat),
                pprust::ty_to_string(&arg.ty))
    }
}

fn span_for_return(ret: &ast::FunctionRetTy) -> Span {
    match *ret {
        ast::FunctionRetTy::NoReturn(ref span) |
        ast::FunctionRetTy::DefaultReturn(ref span) => span.clone(),
        ast::FunctionRetTy::Return(ref ty) => ty.span,
    }
}

fn span_for_ty_param(ty: &ast::TyParam) -> Span {
    // Note that ty.span is the span for ty.ident, not the whole item.
    let lo = ty.span.lo;
    if let Some(ref def) = ty.default {
        return codemap::mk_sp(lo, def.span.hi);
    }
    if ty.bounds.len() == 0 {
        return ty.span;
    }
    let hi = match ty.bounds[ty.bounds.len() - 1] {
        ast::TyParamBound::TraitTyParamBound(ref ptr, _) => ptr.span.hi,
        ast::TyParamBound::RegionTyParamBound(ref l) => l.span.hi,
    };
    codemap::mk_sp(lo, hi)
}

fn span_for_where_pred(pred: &ast::WherePredicate) -> Span {
    match *pred {
        ast::WherePredicate::BoundPredicate(ref p) => p.span,
        ast::WherePredicate::RegionPredicate(ref p) => p.span,
        ast::WherePredicate::EqPredicate(ref p) => p.span,
    }
}