Auto merge of #115979 - GuillaumeGomez:rollup-06ujzgh, r=GuillaumeGomez

Rollup of 6 pull requests

Successful merges:

 - #113383 (style-guide: Add section on bugs, and resolving bugs)
 - #115499 (rustc_target/riscv: Fix passing of transparent unions with only one non-ZST member)
 - #115801 (Detect cycle errors hidden by opaques during monomorphization)
 - #115947 (Custom code classes in docs warning)
 - #115957 (fix mismatched symbols)
 - #115958 (explain mysterious addition in float minimum/maximum)

r? `@ghost`
`@rustbot` modify labels: rollup

compiler/rustc_middle/src/ty/layout.rs

@@ -1118,6 +1118,10 @@ where
     fn is_unit(this: TyAndLayout<'tcx>) -> bool {
         matches!(this.ty.kind(), ty::Tuple(list) if list.len() == 0)
     }
+
+    fn is_transparent(this: TyAndLayout<'tcx>) -> bool {
+        matches!(this.ty.kind(), ty::Adt(def, _) if def.repr().transparent())
+    }
 }
 
 /// Calculates whether a function's ABI can unwind or not.

compiler/rustc_target/src/abi/call/riscv.rs

@@ -89,6 +89,17 @@ where
             }
             FieldsShape::Union(_) => {
                 if !arg_layout.is_zst() {
+                    if arg_layout.is_transparent() {
+                        let non_1zst_elem = arg_layout.non_1zst_field(cx).expect("not exactly one non-1-ZST field in non-ZST repr(transparent) union").1;
+                        return should_use_fp_conv_helper(
+                            cx,
+                            &non_1zst_elem,
+                            xlen,
+                            flen,
+                            field1_kind,
+                            field2_kind,
+                        );
+                    }
                     return Err(CannotUseFpConv);
                 }
             }

compiler/rustc_target/src/abi/mod.rs

@@ -66,6 +66,7 @@ pub trait TyAbiInterface<'a, C>: Sized + std::fmt::Debug {
     fn is_never(this: TyAndLayout<'a, Self>) -> bool;
     fn is_tuple(this: TyAndLayout<'a, Self>) -> bool;
     fn is_unit(this: TyAndLayout<'a, Self>) -> bool;
+    fn is_transparent(this: TyAndLayout<'a, Self>) -> bool;
 }
 
 impl<'a, Ty> TyAndLayout<'a, Ty> {
@@ -136,6 +137,13 @@ impl<'a, Ty> TyAndLayout<'a, Ty> {
         Ty::is_unit(self)
     }
 
+    pub fn is_transparent<C>(self) -> bool
+    where
+        Ty: TyAbiInterface<'a, C>,
+    {
+        Ty::is_transparent(self)
+    }
+
     pub fn offset_of_subfield<C>(self, cx: &C, indices: impl Iterator<Item = usize>) -> Size
     where
         Ty: TyAbiInterface<'a, C>,

compiler/rustc_traits/src/normalize_projection_ty.rs

@@ -3,10 +3,13 @@ use rustc_infer::infer::TyCtxtInferExt;
 use rustc_middle::query::Providers;
 use rustc_middle::ty::{ParamEnvAnd, TyCtxt};
 use rustc_trait_selection::infer::InferCtxtBuilderExt;
+use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt;
 use rustc_trait_selection::traits::query::{
     normalize::NormalizationResult, CanonicalProjectionGoal, NoSolution,
 };
-use rustc_trait_selection::traits::{self, ObligationCause, SelectionContext};
+use rustc_trait_selection::traits::{
+    self, FulfillmentErrorCode, ObligationCause, SelectionContext,
+};
 use std::sync::atomic::Ordering;
 
 pub(crate) fn provide(p: &mut Providers) {
@@ -40,6 +43,27 @@ fn normalize_projection_ty<'tcx>(
                 &mut obligations,
             );
             ocx.register_obligations(obligations);
+            // #112047: With projections and opaques, we are able to create opaques that
+            // are recursive (given some substitution of the opaque's type variables).
+            // In that case, we may only realize a cycle error when calling
+            // `normalize_erasing_regions` in mono.
+            if !ocx.infcx.next_trait_solver() {
+                let errors = ocx.select_where_possible();
+                if !errors.is_empty() {
+                    // Rustdoc may attempt to normalize type alias types which are not
+                    // well-formed. Rustdoc also normalizes types that are just not
+                    // well-formed, since we don't do as much HIR analysis (checking
+                    // that impl vars are constrained by the signature, for example).
+                    if !tcx.sess.opts.actually_rustdoc {
+                        for error in &errors {
+                            if let FulfillmentErrorCode::CodeCycle(cycle) = &error.code {
+                                ocx.infcx.err_ctxt().report_overflow_obligation_cycle(cycle);
+                            }
+                        }
+                    }
+                    return Err(NoSolution);
+                }
+            }
             // FIXME(associated_const_equality): All users of normalize_projection_ty expected
             // a type, but there is the possibility it could've been a const now. Maybe change
             // it to a Term later?