From 312020ef6a39f07d4ba13854dbf4c51c768e9e4c Mon Sep 17 00:00:00 2001
From: Nilstrieb <48135649+Nilstrieb@users.noreply.github.com>
Date: Sun, 26 Feb 2023 08:45:32 +0000
Subject: [PATCH] Remove `from_fn` lang item

It was probably a leftover from the old `?` desugaring but anyways, it's
unused now except for clippy, which can just use a diagnostics item.
---
 compiler/rustc_hir/src/lang_items.rs                        | 2 --
 compiler/rustc_span/src/symbol.rs                           | 1 +
 library/core/src/convert/mod.rs                             | 2 +-
 src/tools/clippy/clippy_lints/src/operators/cmp_owned.rs    | 6 +++---
 .../clippy_lints/src/unnecessary_owned_empty_strings.rs     | 3 ++-
 src/tools/clippy/clippy_lints/src/useless_conversion.rs     | 2 +-
 6 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/compiler/rustc_hir/src/lang_items.rs b/compiler/rustc_hir/src/lang_items.rs
index 04546330915..60fa5a99e10 100644
--- a/compiler/rustc_hir/src/lang_items.rs
+++ b/compiler/rustc_hir/src/lang_items.rs
@@ -302,8 +302,6 @@ language_item_table! {
     Context,                 sym::Context,             context,                    Target::Struct,         GenericRequirement::None;
     FuturePoll,              sym::poll,                future_poll_fn,             Target::Method(MethodKind::Trait { body: false }), GenericRequirement::None;
 
-    FromFrom,                sym::from,                from_fn,                    Target::Method(MethodKind::Trait { body: false }), GenericRequirement::None;
-
     OptionSome,              sym::Some,                option_some_variant,        Target::Variant,        GenericRequirement::None;
     OptionNone,              sym::None,                option_none_variant,        Target::Variant,        GenericRequirement::None;
 
diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs
index 37d2aea42ad..fb579e4ff77 100644
--- a/compiler/rustc_span/src/symbol.rs
+++ b/compiler/rustc_span/src/symbol.rs
@@ -740,6 +740,7 @@ symbols! {
         frem_fast,
         from,
         from_desugaring,
+        from_fn,
         from_iter,
         from_method,
         from_output,
diff --git a/library/core/src/convert/mod.rs b/library/core/src/convert/mod.rs
index f95b880df34..805354be089 100644
--- a/library/core/src/convert/mod.rs
+++ b/library/core/src/convert/mod.rs
@@ -542,7 +542,7 @@ pub trait Into<T>: Sized {
 #[const_trait]
 pub trait From<T>: Sized {
     /// Converts to this type from the input type.
-    #[lang = "from"]
+    #[rustc_diagnostic_item = "from_fn"]
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
     fn from(value: T) -> Self;
diff --git a/src/tools/clippy/clippy_lints/src/operators/cmp_owned.rs b/src/tools/clippy/clippy_lints/src/operators/cmp_owned.rs
index 24aeb82a37f..d3de9699fe9 100644
--- a/src/tools/clippy/clippy_lints/src/operators/cmp_owned.rs
+++ b/src/tools/clippy/clippy_lints/src/operators/cmp_owned.rs
@@ -49,10 +49,10 @@ fn check_op(cx: &LateContext<'_>, expr: &Expr<'_>, other: &Expr<'_>, left: bool)
             (arg, arg.span)
         },
         ExprKind::Call(path, [arg])
-            if path_def_id(cx, path).map_or(false, |id| {
-                if match_def_path(cx, id, &paths::FROM_STR_METHOD) {
+            if path_def_id(cx, path).map_or(false, |did| {
+                if match_def_path(cx, did, &paths::FROM_STR_METHOD) {
                     true
-                } else if cx.tcx.lang_items().from_fn() == Some(id) {
+                } else if cx.tcx.is_diagnostic_item(sym::from_fn, did) {
                     !is_copy(cx, typeck.expr_ty(expr))
                 } else {
                     false
diff --git a/src/tools/clippy/clippy_lints/src/unnecessary_owned_empty_strings.rs b/src/tools/clippy/clippy_lints/src/unnecessary_owned_empty_strings.rs
index 9f207d32fcf..6e802794f5a 100644
--- a/src/tools/clippy/clippy_lints/src/unnecessary_owned_empty_strings.rs
+++ b/src/tools/clippy/clippy_lints/src/unnecessary_owned_empty_strings.rs
@@ -7,6 +7,7 @@ use rustc_hir::{BorrowKind, Expr, ExprKind, LangItem, Mutability};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::ty;
 use rustc_session::{declare_lint_pass, declare_tool_lint};
+use rustc_span::symbol::sym;
 
 declare_clippy_lint! {
     /// ### What it does
@@ -54,7 +55,7 @@ impl<'tcx> LateLintPass<'tcx> for UnnecessaryOwnedEmptyStrings {
                         );
                 } else {
                     if_chain! {
-                        if Some(fun_def_id) == cx.tcx.lang_items().from_fn();
+                        if cx.tcx.is_diagnostic_item(sym::from_fn, fun_def_id);
                         if let [.., last_arg] = args;
                         if let ExprKind::Lit(spanned) = &last_arg.kind;
                         if let LitKind::Str(symbol, _) = spanned.node;
diff --git a/src/tools/clippy/clippy_lints/src/useless_conversion.rs b/src/tools/clippy/clippy_lints/src/useless_conversion.rs
index a95e7b61374..fede625f72a 100644
--- a/src/tools/clippy/clippy_lints/src/useless_conversion.rs
+++ b/src/tools/clippy/clippy_lints/src/useless_conversion.rs
@@ -161,7 +161,7 @@ impl<'tcx> LateLintPass<'tcx> for UselessConversion {
                         }
 
                         if_chain! {
-                            if Some(def_id) == cx.tcx.lang_items().from_fn();
+                            if cx.tcx.is_diagnostic_item(sym::from_fn, def_id);
                             if same_type_and_consts(a, b);
 
                             then {