Auto merge of #9308 - daxpedda:missing-const-for-fn, r=Jarcho

Use `check_proc_macro` for `missing_const_for_fn`

This uses `@Jarcho's` #8694 implementation to fix `missing_const_for_fn` linting in proc-macros.
I'm not 100% sure what I'm doing here, any feedback is appreciated.

Previously: https://github.com/Jarcho/rust-clippy/pull/1.
Fixes #8854.

changelog: [`missing_const_for_fn`]: No longer lints in proc-macros

3 files changed, 54 insertions, 7 deletions

diff --git a/clippy_lints/src/missing_const_for_fn.rs b/clippy_lints/src/missing_const_for_fn.rs
index 2bd920db302..bc304c081b9 100644
--- a/clippy_lints/src/missing_const_for_fn.rs
+++ b/clippy_lints/src/missing_const_for_fn.rs
@@ -1,7 +1,9 @@
 use clippy_utils::diagnostics::span_lint;
 use clippy_utils::qualify_min_const_fn::is_min_const_fn;
 use clippy_utils::ty::has_drop;
-use clippy_utils::{fn_has_unsatisfiable_preds, is_entrypoint_fn, meets_msrv, msrvs, trait_ref_of_method};
+use clippy_utils::{
+    fn_has_unsatisfiable_preds, is_entrypoint_fn, is_from_proc_macro, meets_msrv, msrvs, trait_ref_of_method,
+};
 use rustc_hir as hir;
 use rustc_hir::def_id::CRATE_DEF_ID;
 use rustc_hir::intravisit::FnKind;
@@ -86,10 +88,10 @@ impl MissingConstForFn {
 impl<'tcx> LateLintPass<'tcx> for MissingConstForFn {
     fn check_fn(
         &mut self,
-        cx: &LateContext<'_>,
-        kind: FnKind<'_>,
+        cx: &LateContext<'tcx>,
+        kind: FnKind<'tcx>,
         _: &FnDecl<'_>,
-        _: &Body<'_>,
+        body: &Body<'tcx>,
         span: Span,
         hir_id: HirId,
     ) {
@@ -144,6 +146,10 @@ impl<'tcx> LateLintPass<'tcx> for MissingConstForFn {
             }
         }
 
+        if is_from_proc_macro(cx, &(&kind, body, hir_id, span)) {
+            return;
+        }
+
         let mir = cx.tcx.optimized_mir(def_id);
 
         if let Err((span, err)) = is_min_const_fn(cx.tcx, mir, self.msrv) {
diff --git a/clippy_utils/src/check_proc_macro.rs b/clippy_utils/src/check_proc_macro.rs
index 0f00a1cdf0f..8335ffae81e 100644
--- a/clippy_utils/src/check_proc_macro.rs
+++ b/clippy_utils/src/check_proc_macro.rs
@@ -14,9 +14,9 @@
 
 use rustc_ast::ast::{IntTy, LitIntType, LitKind, StrStyle, UintTy};
 use rustc_hir::{
-    Block, BlockCheckMode, Closure, Destination, Expr, ExprKind, FieldDef, FnHeader, Impl, ImplItem, ImplItemKind,
-    IsAuto, Item, ItemKind, LoopSource, MatchSource, QPath, TraitItem, TraitItemKind, UnOp, UnsafeSource, Unsafety,
-    Variant, VariantData, YieldSource,
+    intravisit::FnKind, Block, BlockCheckMode, Body, Closure, Destination, Expr, ExprKind, FieldDef, FnHeader, HirId,
+    Impl, ImplItem, ImplItemKind, IsAuto, Item, ItemKind, LoopSource, MatchSource, Node, QPath, TraitItem,
+    TraitItemKind, UnOp, UnsafeSource, Unsafety, Variant, VariantData, YieldSource,
 };
 use rustc_lint::{LateContext, LintContext};
 use rustc_middle::ty::TyCtxt;
@@ -250,6 +250,26 @@ fn variant_search_pat(v: &Variant<'_>) -> (Pat, Pat) {
     }
 }
 
+fn fn_kind_pat(tcx: TyCtxt<'_>, kind: &FnKind<'_>, body: &Body<'_>, hir_id: HirId) -> (Pat, Pat) {
+    let (start_pat, end_pat) = match kind {
+        FnKind::ItemFn(.., header) => (fn_header_search_pat(*header), Pat::Str("")),
+        FnKind::Method(.., sig) => (fn_header_search_pat(sig.header), Pat::Str("")),
+        FnKind::Closure => return (Pat::Str(""), expr_search_pat(tcx, &body.value).1),
+    };
+    let start_pat = match tcx.hir().get(hir_id) {
+        Node::Item(Item { vis_span, .. }) | Node::ImplItem(ImplItem { vis_span, .. }) => {
+            if vis_span.is_empty() {
+                start_pat
+            } else {
+                Pat::Str("pub")
+            }
+        },
+        Node::TraitItem(_) => start_pat,
+        _ => Pat::Str(""),
+    };
+    (start_pat, end_pat)
+}
+
 pub trait WithSearchPat {
     type Context: LintContext;
     fn search_pat(&self, cx: &Self::Context) -> (Pat, Pat);
@@ -277,6 +297,18 @@ impl_with_search_pat!(LateContext: ImplItem with impl_item_search_pat);
 impl_with_search_pat!(LateContext: FieldDef with field_def_search_pat);
 impl_with_search_pat!(LateContext: Variant with variant_search_pat);
 
+impl<'cx> WithSearchPat for (&FnKind<'cx>, &Body<'cx>, HirId, Span) {
+    type Context = LateContext<'cx>;
+
+    fn search_pat(&self, cx: &Self::Context) -> (Pat, Pat) {
+        fn_kind_pat(cx.tcx, self.0, self.1, self.2)
+    }
+
+    fn span(&self) -> Span {
+        self.3
+    }
+}
+
 /// Checks if the item likely came from a proc-macro.
 ///
 /// This should be called after `in_external_macro` and the initial pattern matching of the ast as
diff --git a/tests/ui/missing_const_for_fn/cant_be_const.rs b/tests/ui/missing_const_for_fn/cant_be_const.rs
index aa60d0504e5..b950248ef94 100644
--- a/tests/ui/missing_const_for_fn/cant_be_const.rs
+++ b/tests/ui/missing_const_for_fn/cant_be_const.rs
@@ -3,12 +3,16 @@
 //! The .stderr output of this test should be empty. Otherwise it's a bug somewhere.
 
 // aux-build:helper.rs
+// aux-build:../../auxiliary/proc_macro_with_span.rs
 
 #![warn(clippy::missing_const_for_fn)]
 #![feature(start)]
 #![feature(custom_inner_attributes)]
 
 extern crate helper;
+extern crate proc_macro_with_span;
+
+use proc_macro_with_span::with_span;
 
 struct Game;
 
@@ -119,3 +123,8 @@ mod const_fn_stabilized_after_msrv {
         byte.is_ascii_digit();
     }
 }
+
+with_span! {
+    span
+    fn dont_check_in_proc_macro() {}
+}