1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141

//! Check the bodies of `const`s, `static`s and `const fn`s for illegal operations.
//!
//! This module will eventually replace the parts of `qualify_consts.rs` that check whether a local
//! has interior mutability or needs to be dropped, as well as the visitor that emits errors when
//! it finds operations that are invalid in a certain context.

use rustc_attr as attr;
use rustc_hir as hir;
use rustc_hir::def_id::{DefId, LocalDefId};
use rustc_middle::mir;
use rustc_middle::ty::{self, TyCtxt};
use rustc_span::{sym, Symbol};

pub use self::qualifs::Qualif;

pub mod check;
mod ops;
pub mod post_drop_elaboration;
pub mod qualifs;
mod resolver;

/// Information about the item currently being const-checked, as well as a reference to the global
/// context.
pub struct ConstCx<'mir, 'tcx> {
    pub body: &'mir mir::Body<'tcx>,
    pub tcx: TyCtxt<'tcx>,
    pub param_env: ty::ParamEnv<'tcx>,
    pub const_kind: Option<hir::ConstContext>,
}

impl ConstCx<'mir, 'tcx> {
    pub fn new(tcx: TyCtxt<'tcx>, body: &'mir mir::Body<'tcx>) -> Self {
        let def_id = body.source.def_id().expect_local();
        let param_env = tcx.param_env(def_id);
        Self::new_with_param_env(tcx, body, param_env)
    }

    pub fn new_with_param_env(
        tcx: TyCtxt<'tcx>,
        body: &'mir mir::Body<'tcx>,
        param_env: ty::ParamEnv<'tcx>,
    ) -> Self {
        let const_kind = tcx.hir().body_const_context(body.source.def_id().expect_local());
        ConstCx { body, tcx, param_env, const_kind }
    }

    pub fn def_id(&self) -> LocalDefId {
        self.body.source.def_id().expect_local()
    }

    /// Returns the kind of const context this `Item` represents (`const`, `static`, etc.).
    ///
    /// Panics if this `Item` is not const.
    pub fn const_kind(&self) -> hir::ConstContext {
        self.const_kind.expect("`const_kind` must not be called on a non-const fn")
    }

    pub fn is_const_stable_const_fn(&self) -> bool {
        self.const_kind == Some(hir::ConstContext::ConstFn)
            && self.tcx.features().staged_api
            && is_const_stable_const_fn(self.tcx, self.def_id().to_def_id())
    }

    /// Returns the function signature of the item being const-checked if it is a `fn` or `const fn`.
    pub fn fn_sig(&self) -> Option<&'tcx hir::FnSig<'tcx>> {
        // Get this from the HIR map instead of a query to avoid cycle errors.
        //
        // FIXME: Is this still an issue?
        let hir_map = self.tcx.hir();
        let hir_id = hir_map.local_def_id_to_hir_id(self.def_id());
        hir_map.fn_sig_by_hir_id(hir_id)
    }
}

/// Returns `true` if this `DefId` points to one of the official `panic` lang items.
pub fn is_lang_panic_fn(tcx: TyCtxt<'tcx>, def_id: DefId) -> bool {
    Some(def_id) == tcx.lang_items().panic_fn()
        || Some(def_id) == tcx.lang_items().panic_str()
        || Some(def_id) == tcx.lang_items().panic_display()
        || Some(def_id) == tcx.lang_items().begin_panic_fn()
        || Some(def_id) == tcx.lang_items().panic_fmt()
}

/// Returns `true` if this `DefId` points to one of the lang items that will be handled differently
/// in const_eval.
pub fn is_lang_special_const_fn(tcx: TyCtxt<'tcx>, def_id: DefId) -> bool {
    // We can allow calls to these functions because `hook_special_const_fn` in
    // `const_eval/machine.rs` ensures the calls are handled specially.
    // Keep in sync with what that function handles!
    is_lang_panic_fn(tcx, def_id) || Some(def_id) == tcx.lang_items().const_eval_select()
}

pub fn rustc_allow_const_fn_unstable(
    tcx: TyCtxt<'tcx>,
    def_id: DefId,
    feature_gate: Symbol,
) -> bool {
    let attrs = tcx.get_attrs(def_id);
    attr::rustc_allow_const_fn_unstable(&tcx.sess, attrs).any(|name| name == feature_gate)
}

// Returns `true` if the given `const fn` is "const-stable".
//
// Panics if the given `DefId` does not refer to a `const fn`.
//
// Const-stability is only relevant for `const fn` within a `staged_api` crate. Only "const-stable"
// functions can be called in a const-context by users of the stable compiler. "const-stable"
// functions are subject to more stringent restrictions than "const-unstable" functions: They
// cannot use unstable features and can only call other "const-stable" functions.
pub fn is_const_stable_const_fn(tcx: TyCtxt<'tcx>, def_id: DefId) -> bool {
    use attr::{ConstStability, Stability, StabilityLevel};

    // A default body marked const is not const-stable because const
    // trait fns currently cannot be const-stable. We shouldn't
    // restrict default bodies to only call const-stable functions.
    if tcx.has_attr(def_id, sym::default_method_body_is_const) {
        return false;
    }

    // Const-stability is only relevant for `const fn`.
    assert!(tcx.is_const_fn_raw(def_id));

    // Functions with `#[rustc_const_unstable]` are const-unstable.
    match tcx.lookup_const_stability(def_id) {
        Some(ConstStability { level: StabilityLevel::Unstable { .. }, .. }) => return false,
        Some(ConstStability { level: StabilityLevel::Stable { .. }, .. }) => return true,
        None => {}
    }

    // Functions with `#[unstable]` are const-unstable.
    //
    // FIXME(ecstaticmorse): We should keep const-stability attributes wholly separate from normal stability
    // attributes. `#[unstable]` should be irrelevant.
    if let Some(Stability { level: StabilityLevel::Unstable { .. }, .. }) =
        tcx.lookup_stability(def_id)
    {
        return false;
    }

    true
}