diff --git a/clippy_lints/src/transmute.rs b/clippy_lints/src/transmute.rs index ce2ac24f5..d5b694ce3 100644 --- a/clippy_lints/src/transmute.rs +++ b/clippy_lints/src/transmute.rs @@ -7,8 +7,10 @@ use rustc_ast::ast; use rustc_errors::Applicability; use rustc_hir::{Expr, ExprKind, GenericArg, Mutability, QPath, TyKind, UnOp}; use rustc_lint::{LateContext, LateLintPass}; -use rustc_middle::ty::{self, Ty}; +use rustc_middle::ty::{self, cast::CastKind, Ty}; +use rustc_span::DUMMY_SP; use rustc_session::{declare_lint_pass, declare_tool_lint}; +use rustc_typeck::check::{cast::CastCheck, FnCtxt, Inherited}; use std::borrow::Cow; declare_clippy_lint! { @@ -624,7 +626,21 @@ impl<'tcx> LateLintPass<'tcx> for Transmute { ); } }, - _ => return, + (_, _) if can_be_expressed_as_pointer_cast(cx, e, from_ty, to_ty) => { + span_lint( + cx, + TRANSMUTES_EXPRESSIBLE_AS_PTR_CASTS, + e.span, + &format!( + "transmute from `{}` to `{}` which could be expressed as a pointer cast instead", + from_ty, + to_ty + ) + ); + }, + _ => { + return + }, } } } @@ -671,3 +687,57 @@ fn is_layout_incompatible<'tcx>(cx: &LateContext<'tcx>, from: Ty<'tcx>, to: Ty<' false } } + +/// Check if the the type conversion can be expressed as a pointer cast, instead of a transmute. +fn can_be_expressed_as_pointer_cast<'tcx>(cx: &LateContext<'tcx>, e: &'tcx Expr<'_>, from_ty: Ty<'tcx>, to_ty: Ty<'tcx>) -> bool { + use CastKind::*; + matches!( + check_cast(cx, e, from_ty, to_ty), + Some( + PtrPtrCast + | PtrAddrCast + | AddrPtrCast + | ArrayPtrCast + | FnPtrPtrCast + | FnPtrAddrCast + ) + ) +} + +/// If a cast from from_ty to to_ty is valid, returns an Ok containing the kind of the cast. +fn check_cast<'tcx>(cx: &LateContext<'tcx>, e: &'tcx Expr<'_>, from_ty: Ty<'tcx>, to_ty: Ty<'tcx>) -> Option { + let hir_id = e.hir_id; + let local_def_id = hir_id.owner; + + Inherited::build(cx.tcx, local_def_id).enter(|inherited| { + let fn_ctxt = FnCtxt::new( + &inherited, + // TODO should we try to get the correct ParamEnv? + ty::ParamEnv::empty(), + hir_id + ); + + // If we already have errors, we can't be sure we can pointer cast. + if fn_ctxt.errors_reported_since_creation() { + return None; + } + + if let Ok(check) = CastCheck::new( + &fn_ctxt, + e, + from_ty, + to_ty, + // We won't show any error to the user, so we don't care what the span is here. + DUMMY_SP, + DUMMY_SP, + ) { + check.do_check(&fn_ctxt) + .ok() + // do_check's documentation says that it might return Ok and create + // errors in the fcx instead of returing Err in some cases. + .filter(|_| !fn_ctxt.errors_reported_since_creation()) + } else { + None + } + }) +} \ No newline at end of file