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|
//! Detecting lib features (i.e., features that are not lang features).
//!
//! These are declared using stability attributes (e.g., `#[stable (..)]` and `#[unstable (..)]`),
//! but are not declared in one single location (unlike lang features), which means we need to
//! collect them instead.
use rustc_ast::{Attribute, MetaItemKind};
use rustc_attr::{rust_version_symbol, VERSION_PLACEHOLDER};
use rustc_errors::struct_span_err;
use rustc_hir::intravisit::Visitor;
use rustc_middle::hir::nested_filter;
use rustc_middle::middle::lib_features::LibFeatures;
use rustc_middle::ty::query::Providers;
use rustc_middle::ty::TyCtxt;
use rustc_span::symbol::Symbol;
use rustc_span::{sym, Span};
fn new_lib_features() -> LibFeatures {
LibFeatures { stable: Default::default(), unstable: Default::default() }
}
pub struct LibFeatureCollector<'tcx> {
tcx: TyCtxt<'tcx>,
lib_features: LibFeatures,
}
impl<'tcx> LibFeatureCollector<'tcx> {
fn new(tcx: TyCtxt<'tcx>) -> LibFeatureCollector<'tcx> {
LibFeatureCollector { tcx, lib_features: new_lib_features() }
}
fn extract(&self, attr: &Attribute) -> Option<(Symbol, Option<Symbol>, Span)> {
let stab_attrs = [
sym::stable,
sym::unstable,
sym::rustc_const_stable,
sym::rustc_const_unstable,
sym::rustc_default_body_unstable,
];
// Find a stability attribute: one of #[stable(…)], #[unstable(…)],
// #[rustc_const_stable(…)], #[rustc_const_unstable(…)] or #[rustc_default_body_unstable].
if let Some(stab_attr) = stab_attrs.iter().find(|stab_attr| attr.has_name(**stab_attr)) {
let meta_kind = attr.meta_kind();
if let Some(MetaItemKind::List(ref metas)) = meta_kind {
let mut feature = None;
let mut since = None;
for meta in metas {
if let Some(mi) = meta.meta_item() {
// Find the `feature = ".."` meta-item.
match (mi.name_or_empty(), mi.value_str()) {
(sym::feature, val) => feature = val,
(sym::since, val) => since = val,
_ => {}
}
}
}
if let Some(s) = since && s.as_str() == VERSION_PLACEHOLDER {
since = Some(rust_version_symbol());
}
if let Some(feature) = feature {
// This additional check for stability is to make sure we
// don't emit additional, irrelevant errors for malformed
// attributes.
let is_unstable = matches!(
*stab_attr,
sym::unstable
| sym::rustc_const_unstable
| sym::rustc_default_body_unstable
);
if since.is_some() || is_unstable {
return Some((feature, since, attr.span));
}
}
// We need to iterate over the other attributes, because
// `rustc_const_unstable` is not mutually exclusive with
// the other stability attributes, so we can't just `break`
// here.
}
}
None
}
fn collect_feature(&mut self, feature: Symbol, since: Option<Symbol>, span: Span) {
let already_in_stable = self.lib_features.stable.contains_key(&feature);
let already_in_unstable = self.lib_features.unstable.contains_key(&feature);
match (since, already_in_stable, already_in_unstable) {
(Some(since), _, false) => {
if let Some((prev_since, _)) = self.lib_features.stable.get(&feature) {
if *prev_since != since {
self.span_feature_error(
span,
&format!(
"feature `{}` is declared stable since {}, \
but was previously declared stable since {}",
feature, since, prev_since,
),
);
return;
}
}
self.lib_features.stable.insert(feature, (since, span));
}
(None, false, _) => {
self.lib_features.unstable.insert(feature, span);
}
(Some(_), _, true) | (None, true, _) => {
self.span_feature_error(
span,
&format!(
"feature `{}` is declared {}, but was previously declared {}",
feature,
if since.is_some() { "stable" } else { "unstable" },
if since.is_none() { "stable" } else { "unstable" },
),
);
}
}
}
fn span_feature_error(&self, span: Span, msg: &str) {
struct_span_err!(self.tcx.sess, span, E0711, "{}", &msg).emit();
}
}
impl<'tcx> Visitor<'tcx> for LibFeatureCollector<'tcx> {
type NestedFilter = nested_filter::All;
fn nested_visit_map(&mut self) -> Self::Map {
self.tcx.hir()
}
fn visit_attribute(&mut self, attr: &'tcx Attribute) {
if let Some((feature, stable, span)) = self.extract(attr) {
self.collect_feature(feature, stable, span);
}
}
}
fn lib_features(tcx: TyCtxt<'_>, (): ()) -> LibFeatures {
let mut collector = LibFeatureCollector::new(tcx);
tcx.hir().walk_attributes(&mut collector);
collector.lib_features
}
pub fn provide(providers: &mut Providers) {
providers.lib_features = lib_features;
}
|
