src/librustc_typeck/check/demand.rs

   1 // Copyright 2012 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
  12 use check::FnCtxt;
  13 use rustc::infer::InferOk;
  14 use rustc::traits::ObligationCause;
  15
  16 use syntax::ast;
  17 use syntax_pos::{self, Span};
  18 use rustc::hir;
  19 use rustc::hir::def::Def;
  20 use rustc::ty::{self, Ty, AssociatedItem};
  21 use errors::{DiagnosticBuilder, CodeMapper};
  22
  23 use super::method::probe;
  24
  25 impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
  26     // Requires that the two types unify, and prints an error message if
  27     // they don't.
  28     pub fn demand_suptype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
  29         self.demand_suptype_diag(sp, expected, actual).map(|mut e| e.emit());
  30     }
  31
  32     pub fn demand_suptype_diag(&self, sp: Span,
  33                                expected: Ty<'tcx>,
  34                                actual: Ty<'tcx>) -> Option<DiagnosticBuilder<'tcx>> {
  35         let cause = &self.misc(sp);
  36         match self.at(cause, self.param_env).sup(expected, actual) {
  37             Ok(InferOk { obligations, value: () }) => {
  38                 self.register_predicates(obligations);
  39                 None
  40             },
  41             Err(e) => {
  42                 Some(self.report_mismatched_types(&cause, expected, actual, e))
  43             }
  44         }
  45     }
  46
  47     pub fn demand_eqtype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
  48         if let Some(mut err) = self.demand_eqtype_diag(sp, expected, actual) {
  49             err.emit();
  50         }
  51     }
  52
  53     pub fn demand_eqtype_diag(&self,
  54                              sp: Span,
  55                              expected: Ty<'tcx>,
  56                              actual: Ty<'tcx>) -> Option<DiagnosticBuilder<'tcx>> {
  57         self.demand_eqtype_with_origin(&self.misc(sp), expected, actual)
  58     }
  59
  60     pub fn demand_eqtype_with_origin(&self,
  61                                      cause: &ObligationCause<'tcx>,
  62                                      expected: Ty<'tcx>,
  63                                      actual: Ty<'tcx>) -> Option<DiagnosticBuilder<'tcx>> {
  64         match self.at(cause, self.param_env).eq(expected, actual) {
  65             Ok(InferOk { obligations, value: () }) => {
  66                 self.register_predicates(obligations);
  67                 None
  68             },
  69             Err(e) => {
  70                 Some(self.report_mismatched_types(cause, expected, actual, e))
  71             }
  72         }
  73     }
  74
  75     // Checks that the type of `expr` can be coerced to `expected`.
  76     //
  77     // NB: This code relies on `self.diverges` to be accurate.  In
  78     // particular, assignments to `!` will be permitted if the
  79     // diverges flag is currently "always".
  80     pub fn demand_coerce(&self,
  81                          expr: &hir::Expr,
  82                          checked_ty: Ty<'tcx>,
  83                          expected: Ty<'tcx>) {
  84         let expected = self.resolve_type_vars_with_obligations(expected);
  85
  86         if let Err(e) = self.try_coerce(expr, checked_ty, self.diverges.get(), expected) {
  87             let cause = self.misc(expr.span);
  88             let expr_ty = self.resolve_type_vars_with_obligations(checked_ty);
  89             let mut err = self.report_mismatched_types(&cause, expected, expr_ty, e);
  90             if let Some(suggestion) = self.check_ref(expr,
  91                                                      checked_ty,
  92                                                      expected) {
  93                 err.help(&suggestion);
  94             } else {
  95                 let mode = probe::Mode::MethodCall;
  96                 let suggestions = self.probe_for_return_type(syntax_pos::DUMMY_SP,
  97                                                              mode,
  98                                                              expected,
  99                                                              checked_ty,
 100                                                              ast::DUMMY_NODE_ID);
 101                 if suggestions.len() > 0 {
 102                     err.help(&format!("here are some functions which \
 103                                        might fulfill your needs:\n{}",
 104                                       self.get_best_match(&suggestions).join("\n")));
 105                 }
 106             }
 107             err.emit();
 108         }
 109     }
 110
 111     fn format_method_suggestion(&self, method: &AssociatedItem) -> String {
 112         format!("- .{}({})",
 113                 method.name,
 114                 if self.has_no_input_arg(method) {
 115                     ""
 116                 } else {
 117                     "..."
 118                 })
 119     }
 120
 121     fn display_suggested_methods(&self, methods: &[AssociatedItem]) -> Vec<String> {
 122         methods.iter()
 123                .take(5)
 124                .map(|method| self.format_method_suggestion(&*method))
 125                .collect::<Vec<String>>()
 126     }
 127
 128     fn get_best_match(&self, methods: &[AssociatedItem]) -> Vec<String> {
 129         let no_argument_methods: Vec<_> =
 130             methods.iter()
 131                    .filter(|ref x| self.has_no_input_arg(&*x))
 132                    .map(|x| x.clone())
 133                    .collect();
 134         if no_argument_methods.len() > 0 {
 135             self.display_suggested_methods(&no_argument_methods)
 136         } else {
 137             self.display_suggested_methods(&methods)
 138         }
 139     }
 140
 141     // This function checks if the method isn't static and takes other arguments than `self`.
 142     fn has_no_input_arg(&self, method: &AssociatedItem) -> bool {
 143         match method.def() {
 144             Def::Method(def_id) => {
 145                 match self.tcx.type_of(def_id).sty {
 146                     ty::TypeVariants::TyFnDef(_, _, sig) => {
 147                         sig.inputs().skip_binder().len() == 1
 148                     }
 149                     _ => false,
 150                 }
 151             }
 152             _ => false,
 153         }
 154     }
 155
 156     /// This function is used to determine potential "simple" improvements or users' errors and
 157     /// provide them useful help. For example:
 158     ///
 159     /// ```
 160     /// fn some_fn(s: &str) {}
 161     ///
 162     /// let x = "hey!".to_owned();
 163     /// some_fn(x); // error
 164     /// ```
 165     ///
 166     /// No need to find every potential function which could make a coercion to transform a
 167     /// `String` into a `&str` since a `&` would do the trick!
 168     ///
 169     /// In addition of this check, it also checks between references mutability state. If the
 170     /// expected is mutable but the provided isn't, maybe we could just say "Hey, try with
 171     /// `&mut`!".
 172     fn check_ref(&self,
 173                  expr: &hir::Expr,
 174                  checked_ty: Ty<'tcx>,
 175                  expected: Ty<'tcx>)
 176                  -> Option<String> {
 177         match (&expected.sty, &checked_ty.sty) {
 178             (&ty::TyRef(_, _), &ty::TyRef(_, _)) => None,
 179             (&ty::TyRef(_, mutability), _) => {
 180                 // Check if it can work when put into a ref. For example:
 181                 //
 182                 // ```
 183                 // fn bar(x: &mut i32) {}
 184                 //
 185                 // let x = 0u32;
 186                 // bar(&x); // error, expected &mut
 187                 // ```
 188                 let ref_ty = match mutability.mutbl {
 189                     hir::Mutability::MutMutable => self.tcx.mk_mut_ref(
 190                                                        self.tcx.mk_region(ty::ReStatic),
 191                                                        checked_ty),
 192                     hir::Mutability::MutImmutable => self.tcx.mk_imm_ref(
 193                                                        self.tcx.mk_region(ty::ReStatic),
 194                                                        checked_ty),
 195                 };
 196                 if self.can_coerce(ref_ty, expected) {
 197                     // Use the callsite's span if this is a macro call. #41858
 198                     let sp = self.sess().codemap().call_span_if_macro(expr.span);
 199                     if let Ok(src) = self.tcx.sess.codemap().span_to_snippet(sp) {
 200                         return Some(format!("try with `{}{}`",
 201                                             match mutability.mutbl {
 202                                                 hir::Mutability::MutMutable => "&mut ",
 203                                                 hir::Mutability::MutImmutable => "&",
 204                                             },
 205                                             &src));
 206                     }
 207                 }
 208                 None
 209             }
 210             _ => None,
 211         }
 212     }
 213 }