compiler/rustc_typeck/src/structured_errors.rs

   1 use rustc_errors::{Applicability, DiagnosticBuilder, DiagnosticId};
   2 use rustc_middle::ty::{Ty, TypeFoldable};
   3 use rustc_session::Session;
   4 use rustc_span::Span;
   5
   6 pub trait StructuredDiagnostic<'tcx> {
   7     fn session(&self) -> &Session;
   8
   9     fn code(&self) -> DiagnosticId;
  10
  11     fn common(&self) -> DiagnosticBuilder<'tcx>;
  12
  13     fn diagnostic(&self) -> DiagnosticBuilder<'tcx> {
  14         let err = self.common();
  15         if self.session().teach(&self.code()) { self.extended(err) } else { self.regular(err) }
  16     }
  17
  18     fn regular(&self, err: DiagnosticBuilder<'tcx>) -> DiagnosticBuilder<'tcx> {
  19         err
  20     }
  21
  22     fn extended(&self, err: DiagnosticBuilder<'tcx>) -> DiagnosticBuilder<'tcx> {
  23         err
  24     }
  25 }
  26
  27 pub struct VariadicError<'tcx> {
  28     sess: &'tcx Session,
  29     span: Span,
  30     t: Ty<'tcx>,
  31     cast_ty: &'tcx str,
  32 }
  33
  34 impl<'tcx> VariadicError<'tcx> {
  35     pub fn new(
  36         sess: &'tcx Session,
  37         span: Span,
  38         t: Ty<'tcx>,
  39         cast_ty: &'tcx str,
  40     ) -> VariadicError<'tcx> {
  41         VariadicError { sess, span, t, cast_ty }
  42     }
  43 }
  44
  45 impl<'tcx> StructuredDiagnostic<'tcx> for VariadicError<'tcx> {
  46     fn session(&self) -> &Session {
  47         self.sess
  48     }
  49
  50     fn code(&self) -> DiagnosticId {
  51         rustc_errors::error_code!(E0617)
  52     }
  53
  54     fn common(&self) -> DiagnosticBuilder<'tcx> {
  55         let mut err = if self.t.references_error() {
  56             self.sess.diagnostic().struct_dummy()
  57         } else {
  58             self.sess.struct_span_fatal_with_code(
  59                 self.span,
  60                 &format!("can't pass `{}` to variadic function", self.t),
  61                 self.code(),
  62             )
  63         };
  64         if let Ok(snippet) = self.sess.source_map().span_to_snippet(self.span) {
  65             err.span_suggestion(
  66                 self.span,
  67                 &format!("cast the value to `{}`", self.cast_ty),
  68                 format!("{} as {}", snippet, self.cast_ty),
  69                 Applicability::MachineApplicable,
  70             );
  71         } else {
  72             err.help(&format!("cast the value to `{}`", self.cast_ty));
  73         }
  74         err
  75     }
  76
  77     fn extended(&self, mut err: DiagnosticBuilder<'tcx>) -> DiagnosticBuilder<'tcx> {
  78         err.note(&format!(
  79             "certain types, like `{}`, must be cast before passing them to a \
  80                            variadic function, because of arcane ABI rules dictated by the C \
  81                            standard",
  82             self.t
  83         ));
  84         err
  85     }
  86 }
  87
  88 pub struct SizedUnsizedCastError<'tcx> {
  89     sess: &'tcx Session,
  90     span: Span,
  91     expr_ty: Ty<'tcx>,
  92     cast_ty: String,
  93 }
  94
  95 impl<'tcx> SizedUnsizedCastError<'tcx> {
  96     pub fn new(
  97         sess: &'tcx Session,
  98         span: Span,
  99         expr_ty: Ty<'tcx>,
 100         cast_ty: String,
 101     ) -> SizedUnsizedCastError<'tcx> {
 102         SizedUnsizedCastError { sess, span, expr_ty, cast_ty }
 103     }
 104 }
 105
 106 impl<'tcx> StructuredDiagnostic<'tcx> for SizedUnsizedCastError<'tcx> {
 107     fn session(&self) -> &Session {
 108         self.sess
 109     }
 110
 111     fn code(&self) -> DiagnosticId {
 112         rustc_errors::error_code!(E0607)
 113     }
 114
 115     fn common(&self) -> DiagnosticBuilder<'tcx> {
 116         if self.expr_ty.references_error() {
 117             self.sess.diagnostic().struct_dummy()
 118         } else {
 119             self.sess.struct_span_fatal_with_code(
 120                 self.span,
 121                 &format!(
 122                     "cannot cast thin pointer `{}` to fat pointer `{}`",
 123                     self.expr_ty, self.cast_ty
 124                 ),
 125                 self.code(),
 126             )
 127         }
 128     }
 129
 130     fn extended(&self, mut err: DiagnosticBuilder<'tcx>) -> DiagnosticBuilder<'tcx> {
 131         err.help(
 132             "Thin pointers are \"simple\" pointers: they are purely a reference to a
 133 memory address.
 134
 135 Fat pointers are pointers referencing \"Dynamically Sized Types\" (also
 136 called DST). DST don't have a statically known size, therefore they can
 137 only exist behind some kind of pointers that contain additional
 138 information. Slices and trait objects are DSTs. In the case of slices,
 139 the additional information the fat pointer holds is their size.
 140
 141 To fix this error, don't try to cast directly between thin and fat
 142 pointers.
 143
 144 For more information about casts, take a look at The Book:
 145 https://doc.rust-lang.org/reference/expressions/operator-expr.html#type-cast-expressions",
 146         );
 147         err
 148     }
 149 }