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| 1 | +use rustc::hir::map::blocks::FnLikeNode; |
| 2 | +use rustc::ty::query::Providers; |
| 3 | +use rustc::ty::TyCtxt; |
| 4 | +use rustc_hir as hir; |
| 5 | +use rustc_hir::def_id::DefId; |
| 6 | +use rustc_span::symbol::Symbol; |
| 7 | +use rustc_target::spec::abi::Abi; |
| 8 | +use syntax::attr; |
| 9 | + |
| 10 | +/// Whether the `def_id` counts as const fn in your current crate, considering all active |
| 11 | +/// feature gates |
| 12 | +pub fn is_const_fn(tcx: TyCtxt<'_>, def_id: DefId) -> bool { |
| 13 | + tcx.is_const_fn_raw(def_id) |
| 14 | + && match is_unstable_const_fn(tcx, def_id) { |
| 15 | + Some(feature_name) => { |
| 16 | + // has a `rustc_const_unstable` attribute, check whether the user enabled the |
| 17 | + // corresponding feature gate. |
| 18 | + tcx.features().declared_lib_features.iter().any(|&(sym, _)| sym == feature_name) |
| 19 | + } |
| 20 | + // functions without const stability are either stable user written |
| 21 | + // const fn or the user is using feature gates and we thus don't |
| 22 | + // care what they do |
| 23 | + None => true, |
| 24 | + } |
| 25 | +} |
| 26 | + |
| 27 | +/// Whether the `def_id` is an unstable const fn and what feature gate is necessary to enable it |
| 28 | +pub fn is_unstable_const_fn(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Symbol> { |
| 29 | + if tcx.is_const_fn_raw(def_id) { |
| 30 | + let const_stab = tcx.lookup_const_stability(def_id)?; |
| 31 | + if const_stab.level.is_unstable() { Some(const_stab.feature) } else { None } |
| 32 | + } else { |
| 33 | + None |
| 34 | + } |
| 35 | +} |
| 36 | + |
| 37 | +/// Returns `true` if this function must conform to `min_const_fn` |
| 38 | +pub fn is_min_const_fn(tcx: TyCtxt<'_>, def_id: DefId) -> bool { |
| 39 | + // Bail out if the signature doesn't contain `const` |
| 40 | + if !tcx.is_const_fn_raw(def_id) { |
| 41 | + return false; |
| 42 | + } |
| 43 | + |
| 44 | + if tcx.features().staged_api { |
| 45 | + // In order for a libstd function to be considered min_const_fn |
| 46 | + // it needs to be stable and have no `rustc_const_unstable` attribute. |
| 47 | + match tcx.lookup_const_stability(def_id) { |
| 48 | + // `rustc_const_unstable` functions don't need to conform. |
| 49 | + Some(&attr::ConstStability { ref level, .. }) if level.is_unstable() => false, |
| 50 | + None => { |
| 51 | + if let Some(stab) = tcx.lookup_stability(def_id) { |
| 52 | + if stab.level.is_stable() { |
| 53 | + tcx.sess.span_err( |
| 54 | + tcx.def_span(def_id), |
| 55 | + "stable const functions must have either `rustc_const_stable` or \ |
| 56 | + `rustc_const_unstable` attribute", |
| 57 | + ); |
| 58 | + // While we errored above, because we don't know if we need to conform, we |
| 59 | + // err on the "safe" side and require min_const_fn. |
| 60 | + true |
| 61 | + } else { |
| 62 | + // Unstable functions need not conform to min_const_fn. |
| 63 | + false |
| 64 | + } |
| 65 | + } else { |
| 66 | + // Internal functions are forced to conform to min_const_fn. |
| 67 | + // Annotate the internal function with a const stability attribute if |
| 68 | + // you need to use unstable features. |
| 69 | + // Note: this is an arbitrary choice that does not affect stability or const |
| 70 | + // safety or anything, it just changes whether we need to annotate some |
| 71 | + // internal functions with `rustc_const_stable` or with `rustc_const_unstable` |
| 72 | + true |
| 73 | + } |
| 74 | + } |
| 75 | + // Everything else needs to conform, because it would be callable from |
| 76 | + // other `min_const_fn` functions. |
| 77 | + _ => true, |
| 78 | + } |
| 79 | + } else { |
| 80 | + // users enabling the `const_fn` feature gate can do what they want |
| 81 | + !tcx.features().const_fn |
| 82 | + } |
| 83 | +} |
| 84 | + |
| 85 | +pub fn provide(providers: &mut Providers<'_>) { |
| 86 | + /// Const evaluability whitelist is here to check evaluability at the |
| 87 | + /// top level beforehand. |
| 88 | + fn is_const_intrinsic(tcx: TyCtxt<'_>, def_id: DefId) -> Option<bool> { |
| 89 | + match tcx.fn_sig(def_id).abi() { |
| 90 | + Abi::RustIntrinsic | Abi::PlatformIntrinsic => { |
| 91 | + Some(tcx.lookup_const_stability(def_id).is_some()) |
| 92 | + } |
| 93 | + _ => None, |
| 94 | + } |
| 95 | + } |
| 96 | + |
| 97 | + /// Checks whether the function has a `const` modifier or, in case it is an intrinsic, whether |
| 98 | + /// said intrinsic is on the whitelist for being const callable. |
| 99 | + fn is_const_fn_raw(tcx: TyCtxt<'_>, def_id: DefId) -> bool { |
| 100 | + let hir_id = tcx |
| 101 | + .hir() |
| 102 | + .as_local_hir_id(def_id) |
| 103 | + .expect("Non-local call to local provider is_const_fn"); |
| 104 | + |
| 105 | + let node = tcx.hir().get(hir_id); |
| 106 | + |
| 107 | + if let Some(whitelisted) = is_const_intrinsic(tcx, def_id) { |
| 108 | + whitelisted |
| 109 | + } else if let Some(fn_like) = FnLikeNode::from_node(node) { |
| 110 | + fn_like.constness() == hir::Constness::Const |
| 111 | + } else if let hir::Node::Ctor(_) = node { |
| 112 | + true |
| 113 | + } else { |
| 114 | + false |
| 115 | + } |
| 116 | + } |
| 117 | + |
| 118 | + fn is_promotable_const_fn(tcx: TyCtxt<'_>, def_id: DefId) -> bool { |
| 119 | + is_const_fn(tcx, def_id) |
| 120 | + && match tcx.lookup_const_stability(def_id) { |
| 121 | + Some(stab) => { |
| 122 | + if cfg!(debug_assertions) && stab.promotable { |
| 123 | + let sig = tcx.fn_sig(def_id); |
| 124 | + assert_eq!( |
| 125 | + sig.unsafety(), |
| 126 | + hir::Unsafety::Normal, |
| 127 | + "don't mark const unsafe fns as promotable", |
| 128 | + // https://github.com/rust-lang/rust/pull/53851#issuecomment-418760682 |
| 129 | + ); |
| 130 | + } |
| 131 | + stab.promotable |
| 132 | + } |
| 133 | + None => false, |
| 134 | + } |
| 135 | + } |
| 136 | + |
| 137 | + fn const_fn_is_allowed_fn_ptr(tcx: TyCtxt<'_>, def_id: DefId) -> bool { |
| 138 | + is_const_fn(tcx, def_id) |
| 139 | + && tcx |
| 140 | + .lookup_const_stability(def_id) |
| 141 | + .map(|stab| stab.allow_const_fn_ptr) |
| 142 | + .unwrap_or(false) |
| 143 | + } |
| 144 | + |
| 145 | + *providers = Providers { |
| 146 | + is_const_fn_raw, |
| 147 | + is_promotable_const_fn, |
| 148 | + const_fn_is_allowed_fn_ptr, |
| 149 | + ..*providers |
| 150 | + }; |
| 151 | +} |
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