459 lines
16 KiB
Rust
459 lines
16 KiB
Rust
/*!
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# typeck
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The type checker is responsible for:
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1. Determining the type of each expression.
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2. Resolving methods and traits.
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3. Guaranteeing that most type rules are met. ("Most?", you say, "why most?"
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Well, dear reader, read on.)
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The main entry point is [`check_crate()`]. Type checking operates in
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several major phases:
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1. The collect phase first passes over all items and determines their
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type, without examining their "innards".
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2. Variance inference then runs to compute the variance of each parameter.
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3. Coherence checks for overlapping or orphaned impls.
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4. Finally, the check phase then checks function bodies and so forth.
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Within the check phase, we check each function body one at a time
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(bodies of function expressions are checked as part of the
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containing function). Inference is used to supply types wherever
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they are unknown. The actual checking of a function itself has
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several phases (check, regionck, writeback), as discussed in the
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documentation for the [`check`] module.
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The type checker is defined into various submodules which are documented
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independently:
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- astconv: converts the AST representation of types
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into the `ty` representation.
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- collect: computes the types of each top-level item and enters them into
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the `tcx.types` table for later use.
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- coherence: enforces coherence rules, builds some tables.
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- variance: variance inference
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- outlives: outlives inference
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- check: walks over function bodies and type checks them, inferring types for
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local variables, type parameters, etc as necessary.
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- infer: finds the types to use for each type variable such that
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all subtyping and assignment constraints are met. In essence, the check
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module specifies the constraints, and the infer module solves them.
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## Note
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This API is completely unstable and subject to change.
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*/
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#![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
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#![feature(bindings_after_at)]
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#![feature(bool_to_option)]
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#![feature(box_syntax)]
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#![feature(crate_visibility_modifier)]
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#![feature(format_args_capture)]
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#![feature(in_band_lifetimes)]
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#![feature(is_sorted)]
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#![feature(nll)]
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#![feature(or_patterns)]
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#![feature(try_blocks)]
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#![feature(never_type)]
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#![feature(slice_partition_dedup)]
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#![feature(control_flow_enum)]
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#![recursion_limit = "256"]
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#[macro_use]
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extern crate tracing;
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#[macro_use]
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extern crate rustc_middle;
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// These are used by Clippy.
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pub mod check;
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pub mod expr_use_visitor;
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mod astconv;
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mod bounds;
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mod check_unused;
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mod coherence;
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mod collect;
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mod constrained_generic_params;
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mod errors;
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mod impl_wf_check;
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mod mem_categorization;
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mod outlives;
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mod structured_errors;
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mod variance;
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use rustc_errors::{struct_span_err, ErrorReported};
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use rustc_hir as hir;
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use rustc_hir::def_id::{LocalDefId, LOCAL_CRATE};
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use rustc_hir::Node;
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use rustc_infer::infer::{InferOk, TyCtxtInferExt};
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use rustc_infer::traits::TraitEngineExt as _;
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use rustc_middle::middle;
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use rustc_middle::ty::query::Providers;
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use rustc_middle::ty::{self, Ty, TyCtxt};
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use rustc_middle::util;
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use rustc_session::config::EntryFnType;
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use rustc_span::{symbol::sym, Span, DUMMY_SP};
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use rustc_target::spec::abi::Abi;
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use rustc_trait_selection::traits::error_reporting::InferCtxtExt as _;
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use rustc_trait_selection::traits::{
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ObligationCause, ObligationCauseCode, TraitEngine, TraitEngineExt as _,
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};
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use std::iter;
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use astconv::AstConv;
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use bounds::Bounds;
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fn require_c_abi_if_c_variadic(tcx: TyCtxt<'_>, decl: &hir::FnDecl<'_>, abi: Abi, span: Span) {
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match (decl.c_variadic, abi) {
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// The function has the correct calling convention, or isn't a "C-variadic" function.
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(false, _) | (true, Abi::C { .. }) | (true, Abi::Cdecl) => {}
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// The function is a "C-variadic" function with an incorrect calling convention.
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(true, _) => {
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let mut err = struct_span_err!(
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tcx.sess,
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span,
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E0045,
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"C-variadic function must have C or cdecl calling convention"
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);
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err.span_label(span, "C-variadics require C or cdecl calling convention").emit();
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}
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}
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}
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fn require_same_types<'tcx>(
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tcx: TyCtxt<'tcx>,
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cause: &ObligationCause<'tcx>,
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expected: Ty<'tcx>,
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actual: Ty<'tcx>,
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) -> bool {
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tcx.infer_ctxt().enter(|ref infcx| {
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let param_env = ty::ParamEnv::empty();
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let mut fulfill_cx = <dyn TraitEngine<'_>>::new(infcx.tcx);
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match infcx.at(&cause, param_env).eq(expected, actual) {
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Ok(InferOk { obligations, .. }) => {
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fulfill_cx.register_predicate_obligations(infcx, obligations);
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}
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Err(err) => {
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infcx.report_mismatched_types(cause, expected, actual, err).emit();
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return false;
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}
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}
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match fulfill_cx.select_all_or_error(infcx) {
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Ok(()) => true,
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Err(errors) => {
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infcx.report_fulfillment_errors(&errors, None, false);
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false
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}
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}
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})
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}
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fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: LocalDefId) {
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let main_id = tcx.hir().local_def_id_to_hir_id(main_def_id);
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let main_span = tcx.def_span(main_def_id);
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let main_t = tcx.type_of(main_def_id);
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match main_t.kind() {
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ty::FnDef(..) => {
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if let Some(Node::Item(it)) = tcx.hir().find(main_id) {
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if let hir::ItemKind::Fn(ref sig, ref generics, _) = it.kind {
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let mut error = false;
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if !generics.params.is_empty() {
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let msg = "`main` function is not allowed to have generic \
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parameters"
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.to_owned();
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let label = "`main` cannot have generic parameters".to_string();
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struct_span_err!(tcx.sess, generics.span, E0131, "{}", msg)
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.span_label(generics.span, label)
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.emit();
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error = true;
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}
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if let Some(sp) = generics.where_clause.span() {
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struct_span_err!(
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tcx.sess,
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sp,
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E0646,
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"`main` function is not allowed to have a `where` clause"
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)
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.span_label(sp, "`main` cannot have a `where` clause")
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.emit();
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error = true;
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}
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if let hir::IsAsync::Async = sig.header.asyncness {
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let span = tcx.sess.source_map().guess_head_span(it.span);
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struct_span_err!(
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tcx.sess,
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span,
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E0752,
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"`main` function is not allowed to be `async`"
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)
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.span_label(span, "`main` function is not allowed to be `async`")
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.emit();
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error = true;
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}
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let attrs = tcx.hir().attrs(main_id);
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for attr in attrs {
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if tcx.sess.check_name(attr, sym::track_caller) {
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tcx.sess
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.struct_span_err(
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attr.span,
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"`main` function is not allowed to be `#[track_caller]`",
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)
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.span_label(
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main_span,
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"`main` function is not allowed to be `#[track_caller]`",
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)
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.emit();
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error = true;
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}
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}
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if error {
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return;
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}
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}
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}
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let actual = tcx.fn_sig(main_def_id);
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let expected_return_type = if tcx.lang_items().termination().is_some() {
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// we take the return type of the given main function, the real check is done
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// in `check_fn`
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actual.output()
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} else {
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// standard () main return type
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ty::Binder::dummy(tcx.mk_unit())
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};
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let se_ty = tcx.mk_fn_ptr(expected_return_type.map_bound(|expected_return_type| {
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tcx.mk_fn_sig(
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iter::empty(),
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expected_return_type,
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false,
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hir::Unsafety::Normal,
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Abi::Rust,
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)
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}));
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require_same_types(
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tcx,
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&ObligationCause::new(main_span, main_id, ObligationCauseCode::MainFunctionType),
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se_ty,
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tcx.mk_fn_ptr(actual),
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);
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}
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_ => {
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span_bug!(main_span, "main has a non-function type: found `{}`", main_t);
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}
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}
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}
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fn check_start_fn_ty(tcx: TyCtxt<'_>, start_def_id: LocalDefId) {
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let start_id = tcx.hir().local_def_id_to_hir_id(start_def_id);
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let start_span = tcx.def_span(start_def_id);
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let start_t = tcx.type_of(start_def_id);
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match start_t.kind() {
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ty::FnDef(..) => {
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if let Some(Node::Item(it)) = tcx.hir().find(start_id) {
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if let hir::ItemKind::Fn(ref sig, ref generics, _) = it.kind {
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let mut error = false;
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if !generics.params.is_empty() {
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struct_span_err!(
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tcx.sess,
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generics.span,
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E0132,
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"start function is not allowed to have type parameters"
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)
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.span_label(generics.span, "start function cannot have type parameters")
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.emit();
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error = true;
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}
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if let Some(sp) = generics.where_clause.span() {
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struct_span_err!(
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tcx.sess,
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sp,
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E0647,
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"start function is not allowed to have a `where` clause"
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)
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.span_label(sp, "start function cannot have a `where` clause")
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.emit();
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error = true;
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}
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if let hir::IsAsync::Async = sig.header.asyncness {
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let span = tcx.sess.source_map().guess_head_span(it.span);
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struct_span_err!(
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tcx.sess,
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span,
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E0752,
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"`start` is not allowed to be `async`"
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)
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.span_label(span, "`start` is not allowed to be `async`")
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.emit();
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error = true;
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}
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let attrs = tcx.hir().attrs(start_id);
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for attr in attrs {
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if tcx.sess.check_name(attr, sym::track_caller) {
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tcx.sess
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.struct_span_err(
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attr.span,
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"`start` is not allowed to be `#[track_caller]`",
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)
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.span_label(
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start_span,
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"`start` is not allowed to be `#[track_caller]`",
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)
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.emit();
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error = true;
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}
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}
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if error {
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return;
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}
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}
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}
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let se_ty = tcx.mk_fn_ptr(ty::Binder::dummy(tcx.mk_fn_sig(
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[tcx.types.isize, tcx.mk_imm_ptr(tcx.mk_imm_ptr(tcx.types.u8))].iter().cloned(),
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tcx.types.isize,
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false,
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hir::Unsafety::Normal,
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Abi::Rust,
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)));
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require_same_types(
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tcx,
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&ObligationCause::new(start_span, start_id, ObligationCauseCode::StartFunctionType),
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se_ty,
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tcx.mk_fn_ptr(tcx.fn_sig(start_def_id)),
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);
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}
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_ => {
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span_bug!(start_span, "start has a non-function type: found `{}`", start_t);
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}
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}
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}
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fn check_for_entry_fn(tcx: TyCtxt<'_>) {
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match tcx.entry_fn(LOCAL_CRATE) {
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Some((def_id, EntryFnType::Main)) => check_main_fn_ty(tcx, def_id),
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Some((def_id, EntryFnType::Start)) => check_start_fn_ty(tcx, def_id),
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_ => {}
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}
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}
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pub fn provide(providers: &mut Providers) {
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collect::provide(providers);
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coherence::provide(providers);
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check::provide(providers);
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variance::provide(providers);
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outlives::provide(providers);
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impl_wf_check::provide(providers);
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}
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pub fn check_crate(tcx: TyCtxt<'_>) -> Result<(), ErrorReported> {
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let _prof_timer = tcx.sess.timer("type_check_crate");
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// this ensures that later parts of type checking can assume that items
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// have valid types and not error
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// FIXME(matthewjasper) We shouldn't need to use `track_errors`.
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tcx.sess.track_errors(|| {
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tcx.sess.time("type_collecting", || {
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for &module in tcx.hir().krate().modules.keys() {
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tcx.ensure().collect_mod_item_types(module);
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}
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});
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})?;
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if tcx.features().rustc_attrs {
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tcx.sess.track_errors(|| {
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tcx.sess.time("outlives_testing", || outlives::test::test_inferred_outlives(tcx));
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})?;
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}
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tcx.sess.track_errors(|| {
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tcx.sess.time("impl_wf_inference", || impl_wf_check::impl_wf_check(tcx));
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})?;
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tcx.sess.track_errors(|| {
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tcx.sess.time("coherence_checking", || coherence::check_coherence(tcx));
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})?;
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if tcx.features().rustc_attrs {
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tcx.sess.track_errors(|| {
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tcx.sess.time("variance_testing", || variance::test::test_variance(tcx));
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})?;
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}
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tcx.sess.track_errors(|| {
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tcx.sess.time("wf_checking", || check::check_wf_new(tcx));
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})?;
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// NOTE: This is copy/pasted in librustdoc/core.rs and should be kept in sync.
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tcx.sess.time("item_types_checking", || {
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for &module in tcx.hir().krate().modules.keys() {
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tcx.ensure().check_mod_item_types(module);
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}
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});
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tcx.sess.time("item_bodies_checking", || tcx.typeck_item_bodies(LOCAL_CRATE));
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check_unused::check_crate(tcx);
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check_for_entry_fn(tcx);
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if tcx.sess.err_count() == 0 { Ok(()) } else { Err(ErrorReported) }
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}
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/// A quasi-deprecated helper used in rustdoc and clippy to get
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/// the type from a HIR node.
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pub fn hir_ty_to_ty<'tcx>(tcx: TyCtxt<'tcx>, hir_ty: &hir::Ty<'_>) -> Ty<'tcx> {
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// In case there are any projections, etc., find the "environment"
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// def-ID that will be used to determine the traits/predicates in
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// scope. This is derived from the enclosing item-like thing.
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let env_node_id = tcx.hir().get_parent_item(hir_ty.hir_id);
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let env_def_id = tcx.hir().local_def_id(env_node_id);
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let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id.to_def_id());
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item_cx.to_ty(hir_ty)
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}
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pub fn hir_trait_to_predicates<'tcx>(
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tcx: TyCtxt<'tcx>,
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hir_trait: &hir::TraitRef<'_>,
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self_ty: Ty<'tcx>,
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) -> Bounds<'tcx> {
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// In case there are any projections, etc., find the "environment"
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// def-ID that will be used to determine the traits/predicates in
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// scope. This is derived from the enclosing item-like thing.
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let env_hir_id = tcx.hir().get_parent_item(hir_trait.hir_ref_id);
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let env_def_id = tcx.hir().local_def_id(env_hir_id);
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let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id.to_def_id());
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let mut bounds = Bounds::default();
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let _ = <dyn AstConv<'_>>::instantiate_poly_trait_ref_inner(
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&item_cx,
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hir_trait,
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DUMMY_SP,
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hir::Constness::NotConst,
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self_ty,
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&mut bounds,
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true,
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);
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bounds
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}
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