Auto merge of rust-lang#94431 - matthiaskrgr:rollup-1jsj0wu, r=matthiaskrgr

Rollup of 7 pull requests

Successful merges:

 - rust-lang#94396 (1 - Make more use of `let_chains`)
 - rust-lang#94397 (Document that pre-expansion lint passes are softly deprecated)
 - rust-lang#94399 (Add test for rust-lang#79465 to prevent regression)
 - rust-lang#94409 (avoid rebuilding bootstrap when PATH changes)
 - rust-lang#94415 (Use the first codegen backend in the config.toml as default)
 - rust-lang#94417 (Fix duplicated impl links)
 - rust-lang#94420 (3 - Make more use of `let_chains`)

Failed merges:

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

Author: bors

Diff for: compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -1921,17 +1921,16 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                 err.span_label(assigned_span, format!("first assignment to {}", place_description));
             }
         }
-        if let Some(decl) = local_decl {
-            if let Some(name) = local_name {
-                if decl.can_be_made_mutable() {
-                    err.span_suggestion(
-                        decl.source_info.span,
-                        "consider making this binding mutable",
-                        format!("mut {}", name),
-                        Applicability::MachineApplicable,
-                    );
-                }
-            }
+        if let Some(decl) = local_decl
+            && let Some(name) = local_name
+            && decl.can_be_made_mutable()
+        {
+            err.span_suggestion(
+                decl.source_info.span,
+                "consider making this binding mutable",
+                format!("mut {}", name),
+                Applicability::MachineApplicable,
+            );
         }
         err.span_label(span, msg);
         self.buffer_error(err);

Diff for: compiler/rustc_borrowck/src/diagnostics/explain_borrow.rs

@@ -375,15 +375,12 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
 
             Some(Cause::DropVar(local, location)) => {
                 let mut should_note_order = false;
-                if self.local_names[local].is_some() {
-                    if let Some((WriteKind::StorageDeadOrDrop, place)) = kind_place {
-                        if let Some(borrowed_local) = place.as_local() {
-                            if self.local_names[borrowed_local].is_some() && local != borrowed_local
-                            {
-                                should_note_order = true;
-                            }
-                        }
-                    }
+                if self.local_names[local].is_some()
+                    && let Some((WriteKind::StorageDeadOrDrop, place)) = kind_place
+                    && let Some(borrowed_local) = place.as_local()
+                    && self.local_names[borrowed_local].is_some() && local != borrowed_local
+                {
+                    should_note_order = true;
                 }
 
                 BorrowExplanation::UsedLaterWhenDropped {

Diff for: compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs

@@ -1086,21 +1086,17 @@ fn get_mut_span_in_struct_field<'tcx>(
     field: &mir::Field,
 ) -> Option<Span> {
     // Expect our local to be a reference to a struct of some kind.
-    if let ty::Ref(_, ty, _) = ty.kind() {
-        if let ty::Adt(def, _) = ty.kind() {
-            let field = def.all_fields().nth(field.index())?;
-            // Use the HIR types to construct the diagnostic message.
-            let node = tcx.hir().find_by_def_id(field.did.as_local()?)?;
-            // Now we're dealing with the actual struct that we're going to suggest a change to,
-            // we can expect a field that is an immutable reference to a type.
-            if let hir::Node::Field(field) = node {
-                if let hir::TyKind::Rptr(lifetime, hir::MutTy { mutbl: hir::Mutability::Not, ty }) =
-                    field.ty.kind
-                {
-                    return Some(lifetime.span.between(ty.span));
-                }
-            }
-        }
+    if let ty::Ref(_, ty, _) = ty.kind()
+        && let ty::Adt(def, _) = ty.kind()
+        && let field = def.all_fields().nth(field.index())?
+        // Use the HIR types to construct the diagnostic message.
+        && let node = tcx.hir().find_by_def_id(field.did.as_local()?)?
+        // Now we're dealing with the actual struct that we're going to suggest a change to,
+        // we can expect a field that is an immutable reference to a type.
+        && let hir::Node::Field(field) = node
+        && let hir::TyKind::Rptr(lt, hir::MutTy { mutbl: hir::Mutability::Not, ty }) = field.ty.kind
+    {
+        return Some(lt.span.between(ty.span));
     }
 
     None

Diff for: compiler/rustc_borrowck/src/diagnostics/region_errors.rs

@@ -140,14 +140,11 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
 
     /// Returns `true` if a closure is inferred to be an `FnMut` closure.
     fn is_closure_fn_mut(&self, fr: RegionVid) -> bool {
-        if let Some(ty::ReFree(free_region)) = self.to_error_region(fr).as_deref() {
-            if let ty::BoundRegionKind::BrEnv = free_region.bound_region {
-                if let DefiningTy::Closure(_, substs) =
-                    self.regioncx.universal_regions().defining_ty
-                {
-                    return substs.as_closure().kind() == ty::ClosureKind::FnMut;
-                }
-            }
+        if let Some(ty::ReFree(free_region)) = self.to_error_region(fr).as_deref()
+            && let ty::BoundRegionKind::BrEnv = free_region.bound_region
+            && let DefiningTy::Closure(_, substs) = self.regioncx.universal_regions().defining_ty
+        {
+            return substs.as_closure().kind() == ty::ClosureKind::FnMut;
         }
 
         false

Diff for: compiler/rustc_borrowck/src/lib.rs

@@ -1,15 +1,16 @@
 //! This query borrow-checks the MIR to (further) ensure it is not broken.
 
+#![allow(rustc::potential_query_instability)]
 #![feature(bool_to_option)]
 #![feature(box_patterns)]
 #![feature(crate_visibility_modifier)]
+#![feature(let_chains)]
 #![feature(let_else)]
 #![feature(min_specialization)]
 #![feature(stmt_expr_attributes)]
 #![feature(trusted_step)]
 #![feature(try_blocks)]
 #![recursion_limit = "256"]
-#![allow(rustc::potential_query_instability)]
 
 #[macro_use]
 extern crate rustc_middle;
@@ -159,16 +160,14 @@ fn do_mir_borrowck<'a, 'tcx>(
     for var_debug_info in &input_body.var_debug_info {
         if let VarDebugInfoContents::Place(place) = var_debug_info.value {
             if let Some(local) = place.as_local() {
-                if let Some(prev_name) = local_names[local] {
-                    if var_debug_info.name != prev_name {
-                        span_bug!(
-                            var_debug_info.source_info.span,
-                            "local {:?} has many names (`{}` vs `{}`)",
-                            local,
-                            prev_name,
-                            var_debug_info.name
-                        );
-                    }
+                if let Some(prev_name) = local_names[local] && var_debug_info.name != prev_name {
+                    span_bug!(
+                        var_debug_info.source_info.span,
+                        "local {:?} has many names (`{}` vs `{}`)",
+                        local,
+                        prev_name,
+                        var_debug_info.name
+                    );
                 }
                 local_names[local] = Some(var_debug_info.name);
             }

Diff for: compiler/rustc_borrowck/src/places_conflict.rs

@@ -60,10 +60,8 @@ pub(super) fn borrow_conflicts_with_place<'tcx>(
 
     // This Local/Local case is handled by the more general code below, but
     // it's so common that it's a speed win to check for it first.
-    if let Some(l1) = borrow_place.as_local() {
-        if let Some(l2) = access_place.as_local() {
-            return l1 == l2;
-        }
+    if let Some(l1) = borrow_place.as_local() && let Some(l2) = access_place.as_local() {
+        return l1 == l2;
     }
 
     place_components_conflict(tcx, body, borrow_place, borrow_kind, access_place, access, bias)

Diff for: compiler/rustc_interface/src/util.rs

@@ -236,13 +236,9 @@ pub fn get_codegen_backend(
     static LOAD: SyncOnceCell<unsafe fn() -> Box<dyn CodegenBackend>> = SyncOnceCell::new();
 
     let load = LOAD.get_or_init(|| {
-        #[cfg(feature = "llvm")]
-        const DEFAULT_CODEGEN_BACKEND: &str = "llvm";
+        let default_codegen_backend = option_env!("CFG_DEFAULT_CODEGEN_BACKEND").unwrap_or("llvm");
 
-        #[cfg(not(feature = "llvm"))]
-        const DEFAULT_CODEGEN_BACKEND: &str = "cranelift";
-
-        match backend_name.unwrap_or(DEFAULT_CODEGEN_BACKEND) {
+        match backend_name.unwrap_or(default_codegen_backend) {
             filename if filename.contains('.') => load_backend_from_dylib(filename.as_ref()),
             #[cfg(feature = "llvm")]
             "llvm" => rustc_codegen_llvm::LlvmCodegenBackend::new,

Diff for: compiler/rustc_lint/src/context.rs

@@ -166,7 +166,12 @@ impl LintStore {
         self.early_passes.push(Box::new(pass));
     }
 
-    /// Used by clippy.
+    /// This lint pass is softly deprecated. It misses expanded code and has caused a few
+    /// errors in the past. Currently, it is only used in Clippy. New implementations
+    /// should avoid using this interface, as it might be removed in the future.
+    ///
+    /// * See [rust#69838](https://github.com/rust-lang/rust/pull/69838)
+    /// * See [rust-clippy#5518](https://github.com/rust-lang/rust-clippy/pull/5518)
     pub fn register_pre_expansion_pass(
         &mut self,
         pass: impl Fn() -> EarlyLintPassObject + 'static + sync::Send + sync::Sync,

Diff for: compiler/rustc_typeck/src/astconv/mod.rs

@@ -1054,12 +1054,11 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         let mut result = Vec::new();
 
         for ast_bound in ast_bounds {
-            if let Some(trait_ref) = ast_bound.trait_ref() {
-                if let Some(trait_did) = trait_ref.trait_def_id() {
-                    if self.tcx().trait_may_define_assoc_type(trait_did, assoc_name) {
-                        result.push(ast_bound.clone());
-                    }
-                }
+            if let Some(trait_ref) = ast_bound.trait_ref()
+                && let Some(trait_did) = trait_ref.trait_def_id()
+                && self.tcx().trait_may_define_assoc_type(trait_did, assoc_name)
+            {
+                result.push(ast_bound.clone());
             }
         }
 

Diff for: compiler/rustc_typeck/src/check/check.rs

@@ -282,13 +282,12 @@ pub(super) fn check_fn<'a, 'tcx>(
                         sess.span_err(decl.inputs[0].span, "argument should be `&PanicInfo`");
                     }
 
-                    if let Node::Item(item) = hir.get(fn_id) {
-                        if let ItemKind::Fn(_, ref generics, _) = item.kind {
-                            if !generics.params.is_empty() {
+                    if let Node::Item(item) = hir.get(fn_id)
+                        && let ItemKind::Fn(_, ref generics, _) = item.kind
+                        && !generics.params.is_empty()
+                    {
                                 sess.span_err(span, "should have no type parameters");
                             }
-                        }
-                    }
                 } else {
                     let span = sess.source_map().guess_head_span(span);
                     sess.span_err(span, "function should have one argument");
@@ -319,17 +318,15 @@ pub(super) fn check_fn<'a, 'tcx>(
                         sess.span_err(decl.inputs[0].span, "argument should be `Layout`");
                     }
 
-                    if let Node::Item(item) = hir.get(fn_id) {
-                        if let ItemKind::Fn(_, ref generics, _) = item.kind {
-                            if !generics.params.is_empty() {
+                    if let Node::Item(item) = hir.get(fn_id)
+                        && let ItemKind::Fn(_, ref generics, _) = item.kind
+                        && !generics.params.is_empty()
+                    {
                                 sess.span_err(
                                     span,
-                                    "`#[alloc_error_handler]` function should have no type \
-                                     parameters",
+                            "`#[alloc_error_handler]` function should have no type parameters",
                                 );
                             }
-                        }
-                    }
                 } else {
                     let span = sess.source_map().guess_head_span(span);
                     sess.span_err(span, "function should have one argument");
@@ -1146,18 +1143,17 @@ pub(super) fn check_packed(tcx: TyCtxt<'_>, sp: Span, def: &ty::AdtDef) {
     if repr.packed() {
         for attr in tcx.get_attrs(def.did).iter() {
             for r in attr::find_repr_attrs(&tcx.sess, attr) {
-                if let attr::ReprPacked(pack) = r {
-                    if let Some(repr_pack) = repr.pack {
-                        if pack as u64 != repr_pack.bytes() {
+                if let attr::ReprPacked(pack) = r
+                    && let Some(repr_pack) = repr.pack
+                    && pack as u64 != repr_pack.bytes()
+                {
                             struct_span_err!(
                                 tcx.sess,
                                 sp,
                                 E0634,
                                 "type has conflicting packed representation hints"
                             )
                             .emit();
-                        }
-                    }
                 }
             }
         }
@@ -1399,12 +1395,11 @@ fn display_discriminant_value<'tcx>(
 ) -> String {
     if let Some(expr) = &variant.disr_expr {
         let body = &tcx.hir().body(expr.body).value;
-        if let hir::ExprKind::Lit(lit) = &body.kind {
-            if let rustc_ast::LitKind::Int(lit_value, _int_kind) = &lit.node {
-                if evaluated != *lit_value {
+        if let hir::ExprKind::Lit(lit) = &body.kind
+            && let rustc_ast::LitKind::Int(lit_value, _int_kind) = &lit.node
+            && evaluated != *lit_value
+        {
                     return format!("`{}` (overflowed from `{}`)", evaluated, lit_value);
-                }
-            }
         }
     }
     format!("`{}`", evaluated)

Diff for: compiler/rustc_typeck/src/check/coercion.rs

@@ -1696,13 +1696,12 @@ impl<'tcx, 'exprs, E: AsCoercionSite> CoerceMany<'tcx, 'exprs, E> {
     }
 
     fn is_return_ty_unsized<'a>(&self, fcx: &FnCtxt<'a, 'tcx>, blk_id: hir::HirId) -> bool {
-        if let Some((fn_decl, _)) = fcx.get_fn_decl(blk_id) {
-            if let hir::FnRetTy::Return(ty) = fn_decl.output {
-                let ty = <dyn AstConv<'_>>::ast_ty_to_ty(fcx, ty);
-                if let ty::Dynamic(..) = ty.kind() {
+        if let Some((fn_decl, _)) = fcx.get_fn_decl(blk_id)
+            && let hir::FnRetTy::Return(ty) = fn_decl.output
+            && let ty = <dyn AstConv<'_>>::ast_ty_to_ty(fcx, ty)
+            && let ty::Dynamic(..) = ty.kind()
+        {
                     return true;
-                }
-            }
         }
         false
     }

Diff for: compiler/rustc_typeck/src/check/demand.rs

@@ -587,9 +587,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         match (&expr.kind, expected.kind(), checked_ty.kind()) {
             (_, &ty::Ref(_, exp, _), &ty::Ref(_, check, _)) => match (exp.kind(), check.kind()) {
                 (&ty::Str, &ty::Array(arr, _) | &ty::Slice(arr)) if arr == self.tcx.types.u8 => {
-                    if let hir::ExprKind::Lit(_) = expr.kind {
-                        if let Ok(src) = sm.span_to_snippet(sp) {
-                            if replace_prefix(&src, "b\"", "\"").is_some() {
+                    if let hir::ExprKind::Lit(_) = expr.kind
+                        && let Ok(src) = sm.span_to_snippet(sp)
+                        && replace_prefix(&src, "b\"", "\"").is_some()
+                    {
                                 let pos = sp.lo() + BytePos(1);
                                 return Some((
                                     sp.with_hi(pos),
@@ -600,21 +601,19 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                                 ));
                             }
                         }
-                    }
-                }
                 (&ty::Array(arr, _) | &ty::Slice(arr), &ty::Str) if arr == self.tcx.types.u8 => {
-                    if let hir::ExprKind::Lit(_) = expr.kind {
-                        if let Ok(src) = sm.span_to_snippet(sp) {
-                            if replace_prefix(&src, "\"", "b\"").is_some() {
+                    if let hir::ExprKind::Lit(_) = expr.kind
+                        && let Ok(src) = sm.span_to_snippet(sp)
+                        && replace_prefix(&src, "\"", "b\"").is_some()
+                    {
                                 return Some((
                                     sp.shrink_to_lo(),
                                     "consider adding a leading `b`",
                                     "b".to_string(),
                                     Applicability::MachineApplicable,
                                     true,
                                 ));
-                            }
-                        }
+
                     }
                 }
                 _ => {}

Diff for: compiler/rustc_typeck/src/check/expr.rs

@@ -810,10 +810,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         // Use the span of the trailing expression for our cause,
         // not the span of the entire function
         if !explicit_return {
-            if let ExprKind::Block(body, _) = return_expr.kind {
-                if let Some(last_expr) = body.expr {
-                    span = last_expr.span;
-                }
+            if let ExprKind::Block(body, _) = return_expr.kind && let Some(last_expr) = body.expr {
+                span = last_expr.span;
             }
         }
         ret_coercion.borrow_mut().coerce(