Auto merge of #13605 - GnomedDev:read-exact-in-read-exact, r=llogiq

Stop linting unused_io_amount in io traits
Closes#4836
changelog: [`unused_io_amount`] No longer lints inside `io::Read`/`io::Write`, and async variants.

Author: bors

clippy_lints/src/unused_io_amount.rs

@@ -1,6 +1,6 @@
 use clippy_utils::diagnostics::span_lint_hir_and_then;
 use clippy_utils::macros::{is_panic, root_macro_call_first_node};
-use clippy_utils::{is_res_lang_ctor, is_trait_method, match_trait_method, paths, peel_blocks};
+use clippy_utils::{is_res_lang_ctor, is_trait_method,match_def_path,match_trait_method, paths, peel_blocks};
 use hir::{ExprKind,HirId,PatKind};
 use rustc_hir as hir;
 use rustc_lint::{LateContext,LateLintPass};
@@ -83,6 +83,28 @@ impl<'tcx> LateLintPass<'tcx> for UnusedIoAmount {
 /// to consider the arms, and we want to avoid breaking the logic for situations where things
 /// get desugared to match.
 fncheck_block(&mutself,cx:&LateContext<'tcx>,block:&'tcx hir::Block<'tcx>){
+let fn_def_id = block.hir_id.owner.to_def_id();
+ifletSome(impl_id) = cx.tcx.impl_of_method(fn_def_id)
+ && letSome(trait_id) = cx.tcx.trait_id_of_impl(impl_id)
+{
+// We don't want to lint inside io::Read or io::Write implementations, as the author has more
+// information about their trait implementation than our lint, see https://github.com/rust-lang/rust-clippy/issues/4836
+if cx.tcx.is_diagnostic_item(sym::IoRead, trait_id) || cx.tcx.is_diagnostic_item(sym::IoWrite, trait_id){
+return;
+}
+
+let async_paths:[&[&str];4] = [
+&paths::TOKIO_IO_ASYNCREADEXT,
+&paths::TOKIO_IO_ASYNCWRITEEXT,
+&paths::FUTURES_IO_ASYNCREADEXT,
+&paths::FUTURES_IO_ASYNCWRITEEXT,
+];
+
+if async_paths.into_iter().any(|path| match_def_path(cx, trait_id, path)){
+return;
+}
+}
+
 for stmt in block.stmts{
 iflet hir::StmtKind::Semi(exp) = stmt.kind{
 check_expr(cx, exp);

tests/ui/unused_io_amount.rs

@@ -277,4 +277,18 @@ fn allow_works<F: std::io::Read>(mut f: F) {
  f.read(&mut data).unwrap();
 }
 
+structReader{}
+
+implReadforReader{
+fnread(&mutself,buf:&mut[u8]) -> io::Result<usize>{
+todo!()
+}
+
+fnread_exact(&mutself,buf:&mut[u8]) -> io::Result<()>{
+// We shouldn't recommend using Read::read_exact inside Read::read_exact!
+self.read(buf).unwrap();
+Ok(())
+}
+}
+
 fnmain(){}