Rollup merge of #43776 - zackmdavis:feature_gate_fn_must_use, r=alexcrichton
feature-gate #[must_use] for functions as `fn_must_use` @eddyb I [was](https://github.com/rust-lang/rust/pull/43728#issuecomment-320854120) [dithering](https://github.com/rust-lang/rust/pull/43728#issuecomment-320856407) on this, but [your comment](https://github.com/rust-lang/rust/issues/43302#issuecomment-321174989) makes it sound like we do want a feature gate for this? Please advise. r? @eddyb
This commit is contained in:
Corey Farwell
GitHub
commit
1412ff5512
6 changed files with 128 additions and 34 deletions
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@ -160,21 +160,25 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedResults {
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};
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let mut fn_warned = false;
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let maybe_def = match expr.node {
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hir::ExprCall(ref callee, _) => {
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match callee.node {
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hir::ExprPath(ref qpath) => Some(cx.tables.qpath_def(qpath, callee.hir_id)),
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_ => None
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}
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},
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hir::ExprMethodCall(..) => {
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cx.tables.type_dependent_defs().get(expr.hir_id).cloned()
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},
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_ => { None }
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};
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if let Some(def) = maybe_def {
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let def_id = def.def_id();
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fn_warned = check_must_use(cx, def_id, s.span, "return value of ");
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if cx.tcx.sess.features.borrow().fn_must_use {
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let maybe_def = match expr.node {
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hir::ExprCall(ref callee, _) => {
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match callee.node {
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hir::ExprPath(ref qpath) => {
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Some(cx.tables.qpath_def(qpath, callee.hir_id))
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},
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_ => None
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}
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},
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hir::ExprMethodCall(..) => {
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cx.tables.type_dependent_defs().get(expr.hir_id).cloned()
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},
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_ => None
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};
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if let Some(def) = maybe_def {
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let def_id = def.def_id();
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fn_warned = check_must_use(cx, def_id, s.span, "return value of ");
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}
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}
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if !(ty_warned || fn_warned) {
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@ -112,8 +112,8 @@ macro_rules! declare_features {
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// was set. This is most important for knowing when a particular feature became
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// stable (active).
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//
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// NB: The featureck.py script parses this information directly out of the source
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// so take care when modifying it.
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// NB: tools/tidy/src/features.rs parses this information directly out of the
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// source, so take care when modifying it.
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declare_features! (
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(active, asm, "1.0.0", Some(29722)),
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@ -372,6 +372,9 @@ declare_features! (
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// #[doc(cfg(...))]
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(active, doc_cfg, "1.21.0", Some(43781)),
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// allow `#[must_use]` on functions (RFC 1940)
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(active, fn_must_use, "1.21.0", Some(43302)),
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);
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declare_features! (
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@ -915,20 +918,27 @@ struct Context<'a> {
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}
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macro_rules! gate_feature_fn {
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($cx: expr, $has_feature: expr, $span: expr, $name: expr, $explain: expr) => {{
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let (cx, has_feature, span, name, explain) = ($cx, $has_feature, $span, $name, $explain);
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($cx: expr, $has_feature: expr, $span: expr, $name: expr, $explain: expr, $level: expr) => {{
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let (cx, has_feature, span,
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name, explain, level) = ($cx, $has_feature, $span, $name, $explain, $level);
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let has_feature: bool = has_feature(&$cx.features);
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debug!("gate_feature(feature = {:?}, span = {:?}); has? {}", name, span, has_feature);
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if !has_feature && !span.allows_unstable() {
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emit_feature_err(cx.parse_sess, name, span, GateIssue::Language, explain);
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leveled_feature_err(cx.parse_sess, name, span, GateIssue::Language, explain, level)
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.emit();
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}
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}}
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}
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macro_rules! gate_feature {
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($cx: expr, $feature: ident, $span: expr, $explain: expr) => {
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gate_feature_fn!($cx, |x:&Features| x.$feature, $span, stringify!($feature), $explain)
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}
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gate_feature_fn!($cx, |x:&Features| x.$feature, $span,
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stringify!($feature), $explain, GateStrength::Hard)
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};
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($cx: expr, $feature: ident, $span: expr, $explain: expr, $level: expr) => {
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gate_feature_fn!($cx, |x:&Features| x.$feature, $span,
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stringify!($feature), $explain, $level)
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};
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}
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impl<'a> Context<'a> {
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@ -938,7 +948,7 @@ impl<'a> Context<'a> {
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for &(n, ty, ref gateage) in BUILTIN_ATTRIBUTES {
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if name == n {
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if let Gated(_, name, desc, ref has_feature) = *gateage {
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gate_feature_fn!(self, has_feature, attr.span, name, desc);
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gate_feature_fn!(self, has_feature, attr.span, name, desc, GateStrength::Hard);
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}
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debug!("check_attribute: {:?} is builtin, {:?}, {:?}", attr.path, ty, gateage);
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return;
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@ -1008,13 +1018,26 @@ pub enum GateIssue {
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Library(Option<u32>)
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}
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#[derive(Debug, Copy, Clone, PartialEq, Eq)]
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pub enum GateStrength {
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/// A hard error. (Most feature gates should use this.)
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Hard,
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/// Only a warning. (Use this only as backwards-compatibility demands.)
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Soft,
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}
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pub fn emit_feature_err(sess: &ParseSess, feature: &str, span: Span, issue: GateIssue,
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explain: &str) {
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feature_err(sess, feature, span, issue, explain).emit();
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}
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pub fn feature_err<'a>(sess: &'a ParseSess, feature: &str, span: Span, issue: GateIssue,
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explain: &str) -> DiagnosticBuilder<'a> {
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explain: &str) -> DiagnosticBuilder<'a> {
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leveled_feature_err(sess, feature, span, issue, explain, GateStrength::Hard)
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}
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fn leveled_feature_err<'a>(sess: &'a ParseSess, feature: &str, span: Span, issue: GateIssue,
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explain: &str, level: GateStrength) -> DiagnosticBuilder<'a> {
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let diag = &sess.span_diagnostic;
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let issue = match issue {
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@ -1022,10 +1045,15 @@ pub fn feature_err<'a>(sess: &'a ParseSess, feature: &str, span: Span, issue: Ga
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GateIssue::Library(lib) => lib,
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};
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let mut err = if let Some(n) = issue {
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diag.struct_span_err(span, &format!("{} (see issue #{})", explain, n))
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let explanation = if let Some(n) = issue {
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format!("{} (see issue #{})", explain, n)
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} else {
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diag.struct_span_err(span, explain)
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explain.to_owned()
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};
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let mut err = match level {
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GateStrength::Hard => diag.struct_span_err(span, &explanation),
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GateStrength::Soft => diag.struct_span_warn(span, &explanation),
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};
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// #23973: do not suggest `#![feature(...)]` if we are in beta/stable
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@ -1035,7 +1063,15 @@ pub fn feature_err<'a>(sess: &'a ParseSess, feature: &str, span: Span, issue: Ga
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feature));
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}
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// If we're on stable and only emitting a "soft" warning, add a note to
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// clarify that the feature isn't "on" (rather than being on but
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// warning-worthy).
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if !sess.unstable_features.is_nightly_build() && level == GateStrength::Soft {
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err.help("a nightly build of the compiler is required to enable this feature");
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}
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err
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}
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const EXPLAIN_BOX_SYNTAX: &'static str =
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@ -1092,6 +1128,12 @@ macro_rules! gate_feature_post {
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if !span.allows_unstable() {
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gate_feature!(cx.context, $feature, span, $explain)
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}
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}};
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($cx: expr, $feature: ident, $span: expr, $explain: expr, $level: expr) => {{
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let (cx, span) = ($cx, $span);
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if !span.allows_unstable() {
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gate_feature!(cx.context, $feature, span, $explain, $level)
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}
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}}
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}
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@ -1234,6 +1276,11 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
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function may change over time, for now \
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a top-level `fn main()` is required");
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}
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if attr::contains_name(&i.attrs[..], "must_use") {
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gate_feature_post!(&self, fn_must_use, i.span,
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"`#[must_use]` on functions is experimental",
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GateStrength::Soft);
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}
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}
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ast::ItemKind::Struct(..) => {
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@ -1271,7 +1318,7 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
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and possibly buggy");
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}
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ast::ItemKind::Impl(_, polarity, defaultness, _, _, _, _) => {
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ast::ItemKind::Impl(_, polarity, defaultness, _, _, _, ref impl_items) => {
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if polarity == ast::ImplPolarity::Negative {
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gate_feature_post!(&self, optin_builtin_traits,
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i.span,
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@ -1284,6 +1331,16 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
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i.span,
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"specialization is unstable");
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}
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for impl_item in impl_items {
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if let ast::ImplItemKind::Method(..) = impl_item.node {
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if attr::contains_name(&impl_item.attrs[..], "must_use") {
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gate_feature_post!(&self, fn_must_use, impl_item.span,
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"`#[must_use]` on methods is experimental",
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GateStrength::Soft);
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}
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}
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}
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}
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ast::ItemKind::MacroDef(ast::MacroDef { legacy: false, .. }) => {
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31
src/test/compile-fail/feature-gate-fn_must_use.rs
Normal file
31
src/test/compile-fail/feature-gate-fn_must_use.rs
Normal file
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@ -0,0 +1,31 @@
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// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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#![feature(rustc_attrs)]
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struct MyStruct;
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impl MyStruct {
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#[must_use]
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fn need_to_use_method() -> bool { true } //~ WARN `#[must_use]` on methods is experimental
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}
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#[must_use]
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fn need_to_use_it() -> bool { true } //~ WARN `#[must_use]` on functions is experimental
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// Feature gates are tidy-required to have a specially named (or
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// comment-annotated) compile-fail test (which MUST fail), but for
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// backwards-compatibility reasons, we want `#[must_use]` on functions to be
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// compilable even if the `fn_must_use` feature is absent, thus necessitating
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// the usage of `#[rustc_error]` here, pragmatically if awkwardly solving this
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// dilemma until a superior solution can be devised.
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#[rustc_error]
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fn main() {} //~ ERROR compilation successful
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@ -680,6 +680,7 @@ mod must_use {
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mod inner { #![must_use="1400"] }
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#[must_use = "1400"] fn f() { }
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//~^ WARN `#[must_use]` on functions is experimental
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#[must_use = "1400"] struct S;
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@ -8,6 +8,7 @@
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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#![feature(fn_must_use)]
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#![warn(unused_must_use)]
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struct MyStruct {
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@ -1,18 +1,18 @@
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warning: unused return value of `need_to_use_this_value` which must be used: it's important
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--> $DIR/fn_must_use.rs:30:5
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--> $DIR/fn_must_use.rs:31:5
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30 | need_to_use_this_value();
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31 | need_to_use_this_value();
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| ^^^^^^^^^^^^^^^^^^^^^^^^^
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note: lint level defined here
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--> $DIR/fn_must_use.rs:11:9
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--> $DIR/fn_must_use.rs:12:9
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11 | #![warn(unused_must_use)]
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12 | #![warn(unused_must_use)]
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| ^^^^^^^^^^^^^^^
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warning: unused return value of `MyStruct::need_to_use_this_method_value` which must be used
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--> $DIR/fn_must_use.rs:33:5
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--> $DIR/fn_must_use.rs:34:5
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33 | m.need_to_use_this_method_value();
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34 | m.need_to_use_this_method_value();
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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