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Add resolution errors for const generics
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Co-Authored-By: Gabriel Smith <yodaldevoid@users.noreply.github.com>
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@varkor @yodaldevoid
varkor and yodaldevoid committed Feb 7, 2019
1 parent b4ef753 commit ea0d998
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Showing 2 changed files with 146 additions and 32 deletions.
158 changes: 126 additions & 32 deletions src/librustc_resolve/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -51,6 +51,7 @@ use syntax::ast::{FnDecl, ForeignItem, ForeignItemKind, GenericParamKind, Generi
use syntax::ast::{Item, ItemKind, ImplItem, ImplItemKind};
use syntax::ast::{Label, Local, Mutability, Pat, PatKind, Path};
use syntax::ast::{QSelf, TraitItemKind, TraitRef, Ty, TyKind};
use syntax::ast::ParamKindOrd;
use syntax::ptr::P;
use syntax::{span_err, struct_span_err, unwrap_or, walk_list};

Expand Down Expand Up @@ -142,10 +143,11 @@ impl Ord for BindingError {
}

enum ResolutionError<'a> {
/// error E0401: can't use type parameters from outer function
TypeParametersFromOuterFunction(Def),
/// error E0403: the name is already used for a type parameter in this type parameter list
NameAlreadyUsedInTypeParameterList(Name, &'a Span),
/// error E0401: can't use type or const parameters from outer function
ParametersFromOuterFunction(Def, ParamKindOrd),
/// error E0403: the name is already used for a type/const parameter in this list of
/// generic parameters
NameAlreadyUsedInParameterList(Name, &'a Span),
/// error E0407: method is not a member of trait
MethodNotMemberOfTrait(Name, &'a str),
/// error E0437: type is not a member of trait
Expand Down Expand Up @@ -177,7 +179,9 @@ enum ResolutionError<'a> {
/// error E0530: X bindings cannot shadow Ys
BindingShadowsSomethingUnacceptable(&'a str, Name, &'a NameBinding<'a>),
/// error E0128: type parameters with a default cannot use forward declared identifiers
ForwardDeclaredTyParam,
ForwardDeclaredTyParam, // FIXME(const_generics:defaults)
/// error E0670: const parameter cannot depend on type parameter
ConstParamDependentOnTypeParam,
}

/// Combines an error with provided span and emits it
Expand All @@ -195,12 +199,14 @@ fn resolve_struct_error<'sess, 'a>(resolver: &'sess Resolver<'_>,
resolution_error: ResolutionError<'a>)
-> DiagnosticBuilder<'sess> {
match resolution_error {
ResolutionError::TypeParametersFromOuterFunction(outer_def) => {
ResolutionError::ParametersFromOuterFunction(outer_def, kind) => {
let mut err = struct_span_err!(resolver.session,
span,
E0401,
"can't use type parameters from outer function");
err.span_label(span, "use of type variable from outer function");
span,
E0401,
"can't use {} parameters from outer function",
kind,
);
err.span_label(span, format!("use of {} variable from outer function", kind));

let cm = resolver.session.source_map();
match outer_def {
Expand All @@ -224,20 +230,25 @@ fn resolve_struct_error<'sess, 'a>(resolver: &'sess Resolver<'_>,
}
return err;
},
Def::TyParam(typaram_defid) => {
if let Some(typaram_span) = resolver.definitions.opt_span(typaram_defid) {
err.span_label(typaram_span, "type variable from outer function");
Def::TyParam(def_id) => {
if let Some(span) = resolver.definitions.opt_span(def_id) {
err.span_label(span, "type variable from outer function");
}
},
}
Def::ConstParam(def_id) => {
if let Some(span) = resolver.definitions.opt_span(def_id) {
err.span_label(span, "const variable from outer function");
}
}
_ => {
bug!("TypeParametersFromOuterFunction should only be used with Def::SelfTy or \
Def::TyParam")
bug!("TypeParametersFromOuterFunction should only be used with Def::SelfTy, \
Def::TyParam or Def::ConstParam");
}
}

// Try to retrieve the span of the function signature and generate a new message with
// a local type parameter
let sugg_msg = "try using a local type parameter instead";
// a local type or const parameter.
let sugg_msg = &format!("try using a local {} parameter instead", kind);
if let Some((sugg_span, new_snippet)) = cm.generate_local_type_param_snippet(span) {
// Suggest the modification to the user
err.span_suggestion(
Expand All @@ -247,19 +258,20 @@ fn resolve_struct_error<'sess, 'a>(resolver: &'sess Resolver<'_>,
Applicability::MachineApplicable,
);
} else if let Some(sp) = cm.generate_fn_name_span(span) {
err.span_label(sp, "try adding a local type parameter in this method instead");
err.span_label(sp,
format!("try adding a local {} parameter in this method instead", kind));
} else {
err.help("try using a local type parameter instead");
err.help(&format!("try using a local {} parameter instead", kind));
}

err
}
ResolutionError::NameAlreadyUsedInTypeParameterList(name, first_use_span) => {
ResolutionError::NameAlreadyUsedInParameterList(name, first_use_span) => {
let mut err = struct_span_err!(resolver.session,
span,
E0403,
"the name `{}` is already used for a type parameter \
in this type parameter list",
"the name `{}` is already used for a generic \
parameter in this list of generic parameters",
name);
err.span_label(span, "already used");
err.span_label(first_use_span.clone(), format!("first use of `{}`", name));
Expand Down Expand Up @@ -416,6 +428,12 @@ fn resolve_struct_error<'sess, 'a>(resolver: &'sess Resolver<'_>,
span, "defaulted type parameters cannot be forward declared".to_string());
err
}
ResolutionError::ConstParamDependentOnTypeParam => {
let mut err = struct_span_err!(resolver.session, span, E0670,
"const parameters cannot depend on type parameters");
err.span_label(span, format!("const parameter depends on type parameter"));
err
}
}
}

Expand Down Expand Up @@ -546,7 +564,7 @@ impl<'a> PathSource<'a> {
Def::Struct(..) | Def::Union(..) | Def::Enum(..) |
Def::Trait(..) | Def::TraitAlias(..) | Def::TyAlias(..) |
Def::AssociatedTy(..) | Def::PrimTy(..) | Def::TyParam(..) |
Def::SelfTy(..) | Def::Existential(..) |
Def::SelfTy(..) | Def::Existential(..) | Def::ConstParam(..) |
Def::ForeignTy(..) => true,
_ => false,
},
Expand All @@ -564,7 +582,7 @@ impl<'a> PathSource<'a> {
Def::VariantCtor(_, CtorKind::Const) | Def::VariantCtor(_, CtorKind::Fn) |
Def::Const(..) | Def::Static(..) | Def::Local(..) | Def::Upvar(..) |
Def::Fn(..) | Def::Method(..) | Def::AssociatedConst(..) |
Def::SelfCtor(..) => true,
Def::SelfCtor(..) | Def::ConstParam(..) => true,
_ => false,
},
PathSource::Pat => match def {
Expand Down Expand Up @@ -855,6 +873,7 @@ impl<'a, 'tcx> Visitor<'tcx> for Resolver<'a> {
self.label_ribs.pop();
self.ribs[ValueNS].pop();
}

fn visit_generics(&mut self, generics: &'tcx Generics) {
// For type parameter defaults, we have to ban access
// to following type parameters, as the Substs can only
Expand All @@ -865,6 +884,7 @@ impl<'a, 'tcx> Visitor<'tcx> for Resolver<'a> {
let mut found_default = false;
default_ban_rib.bindings.extend(generics.params.iter()
.filter_map(|param| match param.kind {
GenericParamKind::Const { .. } |
GenericParamKind::Lifetime { .. } => None,
GenericParamKind::Type { ref default, .. } => {
found_default |= default.is_some();
Expand All @@ -876,6 +896,16 @@ impl<'a, 'tcx> Visitor<'tcx> for Resolver<'a> {
}
}));

// We also ban access to type parameters for use as the types of const parameters.
let mut const_ty_param_ban_rib = Rib::new(TyParamAsConstParamTy);
const_ty_param_ban_rib.bindings.extend(generics.params.iter()
.filter(|param| if let GenericParamKind::Type { .. } = param.kind {
true
} else {
false
})
.map(|param| (Ident::with_empty_ctxt(param.ident.name), Def::Err)));

for param in &generics.params {
match param.kind {
GenericParamKind::Lifetime { .. } => self.visit_generic_param(param),
Expand All @@ -893,6 +923,17 @@ impl<'a, 'tcx> Visitor<'tcx> for Resolver<'a> {
// Allow all following defaults to refer to this type parameter.
default_ban_rib.bindings.remove(&Ident::with_empty_ctxt(param.ident.name));
}
GenericParamKind::Const { ref ty } => {
self.ribs[TypeNS].push(const_ty_param_ban_rib);

for bound in &param.bounds {
self.visit_param_bound(bound);
}

self.visit_ty(ty);

const_ty_param_ban_rib = self.ribs[TypeNS].pop().unwrap();
}
}
}
for p in &generics.where_clause.predicates {
Expand Down Expand Up @@ -944,6 +985,9 @@ enum RibKind<'a> {
/// from the default of a type parameter because they're not declared
/// before said type parameter. Also see the `visit_generics` override.
ForwardTyParamBanRibKind,

/// We forbid the use of type parameters as the types of const parameters.
TyParamAsConstParamTy,
}

/// One local scope.
Expand Down Expand Up @@ -2535,7 +2579,7 @@ impl<'a> Resolver<'a> {

if seen_bindings.contains_key(&ident) {
let span = seen_bindings.get(&ident).unwrap();
let err = ResolutionError::NameAlreadyUsedInTypeParameterList(
let err = ResolutionError::NameAlreadyUsedInParameterList(
ident.name,
span,
);
Expand All @@ -2548,6 +2592,24 @@ impl<'a> Resolver<'a> {
function_type_rib.bindings.insert(ident, def);
self.record_def(param.id, PathResolution::new(def));
}
GenericParamKind::Const { .. } => {
let ident = param.ident.modern();
debug!("with_type_parameter_rib: {}", param.id);

if seen_bindings.contains_key(&ident) {
let span = seen_bindings.get(&ident).unwrap();
let err = ResolutionError::NameAlreadyUsedInParameterList(
ident.name,
span,
);
resolve_error(self, param.ident.span, err);
}
seen_bindings.entry(ident).or_insert(param.ident.span);

let def = Def::ConstParam(self.definitions.local_def_id(param.id));
function_type_rib.bindings.insert(ident, def);
self.record_def(param.id, PathResolution::new(def));
}
}
}
self.ribs[TypeNS].push(function_type_rib);
Expand Down Expand Up @@ -4106,6 +4168,15 @@ impl<'a> Resolver<'a> {
return Def::Err;
}

// An invalid use of a type parameter as the type of a const parameter.
if let TyParamAsConstParamTy = self.ribs[ns][rib_index].kind {
if record_used {
resolve_error(self, span, ResolutionError::ConstParamDependentOnTypeParam);
}
assert_eq!(def, Def::Err);
return Def::Err;
}

match def {
Def::Upvar(..) => {
span_bug!(span, "unexpected {:?} in bindings", def)
Expand All @@ -4114,7 +4185,7 @@ impl<'a> Resolver<'a> {
for rib in ribs {
match rib.kind {
NormalRibKind | ModuleRibKind(..) | MacroDefinition(..) |
ForwardTyParamBanRibKind => {
ForwardTyParamBanRibKind | TyParamAsConstParamTy => {
// Nothing to do. Continue.
}
ClosureRibKind(function_id) => {
Expand Down Expand Up @@ -4167,21 +4238,44 @@ impl<'a> Resolver<'a> {
match rib.kind {
NormalRibKind | TraitOrImplItemRibKind | ClosureRibKind(..) |
ModuleRibKind(..) | MacroDefinition(..) | ForwardTyParamBanRibKind |
ConstantItemRibKind => {
ConstantItemRibKind | TyParamAsConstParamTy => {
// Nothing to do. Continue.
}
ItemRibKind => {
// This was an attempt to use a type parameter outside
// its scope.
// This was an attempt to use a type parameter outside its scope.
if record_used {
resolve_error(self, span,
ResolutionError::TypeParametersFromOuterFunction(def));
resolve_error(
self,
span,
ResolutionError::ParametersFromOuterFunction(
def,
ParamKindOrd::Type,
),
);
}
return Def::Err;
}
}
}
}
Def::ConstParam(..) => {
for rib in ribs {
if let ItemRibKind = rib.kind {
// This was an attempt to use a const parameter outside its scope.
if record_used {
resolve_error(
self,
span,
ResolutionError::ParametersFromOuterFunction(
def,
ParamKindOrd::Const,
),
);
}
return Def::Err;
}
}
}
_ => {}
}
def
Expand Down
20 changes: 20 additions & 0 deletions src/libsyntax/ast.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -307,6 +307,26 @@ impl GenericBound {

pub type GenericBounds = Vec<GenericBound>;

/// Specifies the enforced ordering for generic parameters. In the future,
/// if we wanted to relax this order, we could override `PartialEq` and
/// `PartialOrd`, to allow the kinds to be unordered.
#[derive(PartialEq, Eq, PartialOrd, Ord, Hash, Clone, Copy)]
pub enum ParamKindOrd {
Lifetime,
Type,
Const,
}

impl fmt::Display for ParamKindOrd {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
match self {
ParamKindOrd::Lifetime => "lifetime".fmt(f),
ParamKindOrd::Type => "type".fmt(f),
ParamKindOrd::Const => "const".fmt(f),
}
}
}

#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
pub enum GenericParamKind {
/// A lifetime definition (e.g., `'a: 'b + 'c + 'd`).
Expand Down

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