rustc_hir_typeck/
check.rs

Help
1use std::cell::RefCell;
2
3use rustc_abi::ExternAbi;
4use rustc_hir as hir;
5use rustc_hir::def::DefKind;
6use rustc_hir::intravisit::Visitor;
7use rustc_hir::lang_items::LangItem;
8use rustc_hir_analysis::check::{check_function_signature, forbid_intrinsic_abi};
9use rustc_infer::infer::RegionVariableOrigin;
10use rustc_infer::traits::WellFormedLoc;
11use rustc_middle::ty::{self, Binder, Ty, TyCtxt};
12use rustc_span::def_id::LocalDefId;
13use rustc_span::sym;
14use rustc_trait_selection::traits::{ObligationCause, ObligationCauseCode};
15use tracing::{debug, instrument};
16
17use crate::coercion::CoerceMany;
18use crate::gather_locals::GatherLocalsVisitor;
19use crate::{CoroutineTypes, Diverges, FnCtxt};
20
21/// Helper used for fns and closures. Does the grungy work of checking a function
22/// body and returns the function context used for that purpose, since in the case of a fn item
23/// there is still a bit more to do.
24///
25/// * ...
26/// * inherited: other fields inherited from the enclosing fn (if any)
27#[instrument(skip(fcx, body), level = "debug")]
28pub(super) fn check_fn<'a, 'tcx>(
29    fcx: &mut FnCtxt<'a, 'tcx>,
30    fn_sig: ty::FnSig<'tcx>,
31    coroutine_types: Option<CoroutineTypes<'tcx>>,
32    decl: &'tcx hir::FnDecl<'tcx>,
33    fn_def_id: LocalDefId,
34    body: &'tcx hir::Body<'tcx>,
35    params_can_be_unsized: bool,
36) -> Option<CoroutineTypes<'tcx>> {
37    let fn_id = fcx.tcx.local_def_id_to_hir_id(fn_def_id);
38    let tcx = fcx.tcx;
39    let declared_ret_ty = fn_sig.output();
40    let ret_ty =
41        fcx.register_infer_ok_obligations(fcx.infcx.replace_opaque_types_with_inference_vars(
42            declared_ret_ty,
43            fn_def_id,
44            decl.output.span(),
45            fcx.param_env,
46        ));
47
48    fcx.coroutine_types = coroutine_types;
49    fcx.ret_coercion = Some(RefCell::new(CoerceMany::new(ret_ty)));
50
51    let span = body.value.span;
52
53    forbid_intrinsic_abi(tcx, span, fn_sig.abi);
54
55    GatherLocalsVisitor::new(fcx).visit_body(body);
56
57    // C-variadic fns also have a `VaList` input that's not listed in `fn_sig`
58    // (as it's created inside the body itself, not passed in from outside).
59    let maybe_va_list = fn_sig.c_variadic.then(|| {
60        let span = body.params.last().unwrap().span;
61        let va_list_did = tcx.require_lang_item(LangItem::VaList, Some(span));
62        let region = fcx.next_region_var(RegionVariableOrigin::MiscVariable(span));
63
64        tcx.type_of(va_list_did).instantiate(tcx, &[region.into()])
65    });
66
67    // Add formal parameters.
68    let inputs_hir = tcx.hir_fn_decl_by_hir_id(fn_id).map(|decl| &decl.inputs);
69    let inputs_fn = fn_sig.inputs().iter().copied();
70    for (idx, (param_ty, param)) in inputs_fn.chain(maybe_va_list).zip(body.params).enumerate() {
71        // We checked the root's signature during wfcheck, but not the child.
72        if fcx.tcx.is_typeck_child(fn_def_id.to_def_id()) {
73            fcx.register_wf_obligation(
74                param_ty.into(),
75                param.span,
76                ObligationCauseCode::WellFormed(Some(WellFormedLoc::Param {
77                    function: fn_def_id,
78                    param_idx: idx,
79                })),
80            );
81        }
82
83        // Check the pattern.
84        let ty: Option<&hir::Ty<'_>> = inputs_hir.and_then(|h| h.get(idx));
85        let ty_span = ty.map(|ty| ty.span);
86        fcx.check_pat_top(param.pat, param_ty, ty_span, None, None);
87        if param.pat.is_never_pattern() {
88            fcx.function_diverges_because_of_empty_arguments.set(Diverges::Always {
89                span: param.pat.span,
90                custom_note: Some("any code following a never pattern is unreachable"),
91            });
92        }
93
94        // Check that argument is Sized.
95        if !params_can_be_unsized {
96            fcx.require_type_is_sized(
97                param_ty,
98                param.ty_span,
99                // ty.span == binding_span iff this is a closure parameter with no type ascription,
100                // or if it's an implicit `self` parameter
101                ObligationCauseCode::SizedArgumentType(
102                    if ty_span == Some(param.span) && tcx.is_closure_like(fn_def_id.into()) {
103                        None
104                    } else {
105                        ty.map(|ty| ty.hir_id)
106                    },
107                ),
108            );
109        }
110
111        fcx.write_ty(param.hir_id, param_ty);
112    }
113
114    fcx.typeck_results.borrow_mut().liberated_fn_sigs_mut().insert(fn_id, fn_sig);
115
116    // We checked the root's ret ty during wfcheck, but not the child.
117    if fcx.tcx.is_typeck_child(fn_def_id.to_def_id()) {
118        let return_or_body_span = match decl.output {
119            hir::FnRetTy::DefaultReturn(_) => body.value.span,
120            hir::FnRetTy::Return(ty) => ty.span,
121        };
122
123        fcx.require_type_is_sized(
124            declared_ret_ty,
125            return_or_body_span,
126            ObligationCauseCode::SizedReturnType,
127        );
128    }
129
130    fcx.is_whole_body.set(true);
131    fcx.check_return_or_body_tail(body.value, false);
132
133    // Finalize the return check by taking the LUB of the return types
134    // we saw and assigning it to the expected return type. This isn't
135    // really expected to fail, since the coercions would have failed
136    // earlier when trying to find a LUB.
137    let coercion = fcx.ret_coercion.take().unwrap().into_inner();
138    let mut actual_return_ty = coercion.complete(fcx);
139    debug!("actual_return_ty = {:?}", actual_return_ty);
140    if let ty::Dynamic(..) = declared_ret_ty.kind() {
141        // We have special-cased the case where the function is declared
142        // `-> dyn Foo` and we don't actually relate it to the
143        // `fcx.ret_coercion`, so just instantiate a type variable.
144        actual_return_ty = fcx.next_ty_var(span);
145        debug!("actual_return_ty replaced with {:?}", actual_return_ty);
146    }
147
148    // HACK(oli-obk, compiler-errors): We should be comparing this against
149    // `declared_ret_ty`, but then anything uninferred would be inferred to
150    // the opaque type itself. That again would cause writeback to assume
151    // we have a recursive call site and do the sadly stabilized fallback to `()`.
152    fcx.demand_suptype(span, ret_ty, actual_return_ty);
153
154    // Check that a function marked as `#[panic_handler]` has signature `fn(&PanicInfo) -> !`
155    if tcx.is_lang_item(fn_def_id.to_def_id(), LangItem::PanicImpl) {
156        check_panic_info_fn(tcx, fn_def_id, fn_sig);
157    }
158
159    if tcx.is_lang_item(fn_def_id.to_def_id(), LangItem::Start) {
160        check_lang_start_fn(tcx, fn_sig, fn_def_id);
161    }
162
163    fcx.coroutine_types
164}
165
166fn check_panic_info_fn(tcx: TyCtxt<'_>, fn_id: LocalDefId, fn_sig: ty::FnSig<'_>) {
167    let span = tcx.def_span(fn_id);
168
169    let DefKind::Fn = tcx.def_kind(fn_id) else {
170        tcx.dcx().span_err(span, "should be a function");
171        return;
172    };
173
174    let generic_counts = tcx.generics_of(fn_id).own_counts();
175    if generic_counts.types != 0 {
176        tcx.dcx().span_err(span, "should have no type parameters");
177    }
178    if generic_counts.consts != 0 {
179        tcx.dcx().span_err(span, "should have no const parameters");
180    }
181
182    let panic_info_did = tcx.require_lang_item(hir::LangItem::PanicInfo, Some(span));
183
184    // build type `for<'a, 'b> fn(&'a PanicInfo<'b>) -> !`
185    let panic_info_ty = tcx.type_of(panic_info_did).instantiate(
186        tcx,
187        &[ty::GenericArg::from(ty::Region::new_bound(
188            tcx,
189            ty::INNERMOST,
190            ty::BoundRegion { var: ty::BoundVar::from_u32(1), kind: ty::BoundRegionKind::Anon },
191        ))],
192    );
193    let panic_info_ref_ty = Ty::new_imm_ref(
194        tcx,
195        ty::Region::new_bound(
196            tcx,
197            ty::INNERMOST,
198            ty::BoundRegion { var: ty::BoundVar::ZERO, kind: ty::BoundRegionKind::Anon },
199        ),
200        panic_info_ty,
201    );
202
203    let bounds = tcx.mk_bound_variable_kinds(&[
204        ty::BoundVariableKind::Region(ty::BoundRegionKind::Anon),
205        ty::BoundVariableKind::Region(ty::BoundRegionKind::Anon),
206    ]);
207    let expected_sig = ty::Binder::bind_with_vars(
208        tcx.mk_fn_sig([panic_info_ref_ty], tcx.types.never, false, fn_sig.safety, ExternAbi::Rust),
209        bounds,
210    );
211
212    let _ = check_function_signature(
213        tcx,
214        ObligationCause::new(span, fn_id, ObligationCauseCode::LangFunctionType(sym::panic_impl)),
215        fn_id.into(),
216        expected_sig,
217    );
218}
219
220fn check_lang_start_fn<'tcx>(tcx: TyCtxt<'tcx>, fn_sig: ty::FnSig<'tcx>, def_id: LocalDefId) {
221    // build type `fn(main: fn() -> T, argc: isize, argv: *const *const u8, sigpipe: u8)`
222
223    // make a Ty for the generic on the fn for diagnostics
224    // FIXME: make the lang item generic checks check for the right generic *kind*
225    // for example `start`'s generic should be a type parameter
226    let generics = tcx.generics_of(def_id);
227    let fn_generic = generics.param_at(0, tcx);
228    let generic_ty = Ty::new_param(tcx, fn_generic.index, fn_generic.name);
229    let main_fn_ty = Ty::new_fn_ptr(
230        tcx,
231        Binder::dummy(tcx.mk_fn_sig([], generic_ty, false, hir::Safety::Safe, ExternAbi::Rust)),
232    );
233
234    let expected_sig = ty::Binder::dummy(tcx.mk_fn_sig(
235        [
236            main_fn_ty,
237            tcx.types.isize,
238            Ty::new_imm_ptr(tcx, Ty::new_imm_ptr(tcx, tcx.types.u8)),
239            tcx.types.u8,
240        ],
241        tcx.types.isize,
242        false,
243        fn_sig.safety,
244        ExternAbi::Rust,
245    ));
246
247    let _ = check_function_signature(
248        tcx,
249        ObligationCause::new(
250            tcx.def_span(def_id),
251            def_id,
252            ObligationCauseCode::LangFunctionType(sym::start),
253        ),
254        def_id.into(),
255        expected_sig,
256    );
257}
rustc_hir_typeck/check.rs

rustc_hir_typeck/
check.rs
