Rollup merge of rust-lang#94143 - est31:let_else_const_eval, r=lcnr

rustc_const_eval: adopt let else in more places

Continuation of rust-lang#89933, rust-lang#91018, rust-lang#91481, rust-lang#93046, rust-lang#93590, rust-lang#94011.

I have extended my clippy lint to also recognize tuple passing and match statements. The diff caused by fixing it is way above 1 thousand lines. Thus, I split it up into multiple pull requests to make reviewing easier. This PR handles rustc_const_eval.

compiler/rustc_const_eval/src/const_eval/eval_queries.rs

@@ -231,9 +231,8 @@ pub fn eval_to_const_value_raw_provider<'tcx>(
     // Catch such calls and evaluate them instead of trying to load a constant's MIR.
     if let ty::InstanceDef::Intrinsic(def_id) = key.value.instance.def {
         let ty = key.value.instance.ty(tcx, key.param_env);
-        let substs = match ty.kind() {
-            ty::FnDef(_, substs) => substs,
-            _ => bug!("intrinsic with type {:?}", ty),
+        let ty::FnDef(_, substs) = ty.kind() else {
+            bug!("intrinsic with type {:?}", ty);
         };
         return eval_nullary_intrinsic(tcx, key.param_env, def_id, substs).map_err(|error| {
             let span = tcx.def_span(def_id);

compiler/rustc_const_eval/src/const_eval/machine.rs

@@ -318,15 +318,12 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
         let intrinsic_name = ecx.tcx.item_name(instance.def_id());
 
         // CTFE-specific intrinsics.
-        let (dest, ret) = match ret {
-            None => {
-                return Err(ConstEvalErrKind::NeedsRfc(format!(
-                    "calling intrinsic `{}`",
-                    intrinsic_name
-                ))
-                .into());
-            }
-            Some(p) => p,
+        let Some((dest, ret)) = ret else {
+            return Err(ConstEvalErrKind::NeedsRfc(format!(
+                "calling intrinsic `{}`",
+                intrinsic_name
+            ))
+            .into());
         };
         match intrinsic_name {
             sym::ptr_guaranteed_eq | sym::ptr_guaranteed_ne => {

compiler/rustc_const_eval/src/interpret/eval_context.rs

@@ -631,15 +631,11 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 // the last field).  Can't have foreign types here, how would we
                 // adjust alignment and size for them?
                 let field = layout.field(self, layout.fields.count() - 1);
-                let (unsized_size, unsized_align) =
-                    match self.size_and_align_of(metadata, &field)? {
-                        Some(size_and_align) => size_and_align,
-                        None => {
-                            // A field with an extern type. We don't know the actual dynamic size
-                            // or the alignment.
-                            return Ok(None);
-                        }
-                    };
+                let Some((unsized_size, unsized_align)) = self.size_and_align_of(metadata, &field)? else {
+                    // A field with an extern type. We don't know the actual dynamic size
+                    // or the alignment.
+                    return Ok(None);
+                };
 
                 // FIXME (#26403, #27023): We should be adding padding
                 // to `sized_size` (to accommodate the `unsized_align`

compiler/rustc_const_eval/src/interpret/intern.rs

@@ -84,22 +84,19 @@ fn intern_shallow<'rt, 'mir, 'tcx, M: CompileTimeMachine<'mir, 'tcx, const_eval:
     trace!("intern_shallow {:?} with {:?}", alloc_id, mode);
     // remove allocation
     let tcx = ecx.tcx;
-    let (kind, mut alloc) = match ecx.memory.alloc_map.remove(&alloc_id) {
-        Some(entry) => entry,
-        None => {
-            // Pointer not found in local memory map. It is either a pointer to the global
-            // map, or dangling.
-            // If the pointer is dangling (neither in local nor global memory), we leave it
-            // to validation to error -- it has the much better error messages, pointing out where
-            // in the value the dangling reference lies.
-            // The `delay_span_bug` ensures that we don't forget such a check in validation.
-            if tcx.get_global_alloc(alloc_id).is_none() {
-                tcx.sess.delay_span_bug(ecx.tcx.span, "tried to intern dangling pointer");
-            }
-            // treat dangling pointers like other statics
-            // just to stop trying to recurse into them
-            return Some(IsStaticOrFn);
+    let Some((kind, mut alloc)) = ecx.memory.alloc_map.remove(&alloc_id) else {
+        // Pointer not found in local memory map. It is either a pointer to the global
+        // map, or dangling.
+        // If the pointer is dangling (neither in local nor global memory), we leave it
+        // to validation to error -- it has the much better error messages, pointing out where
+        // in the value the dangling reference lies.
+        // The `delay_span_bug` ensures that we don't forget such a check in validation.
+        if tcx.get_global_alloc(alloc_id).is_none() {
+            tcx.sess.delay_span_bug(ecx.tcx.span, "tried to intern dangling pointer");
         }
+        // treat dangling pointers like other statics
+        // just to stop trying to recurse into them
+        return Some(IsStaticOrFn);
     };
     // This match is just a canary for future changes to `MemoryKind`, which most likely need
     // changes in this function.

compiler/rustc_const_eval/src/interpret/memory.rs

@@ -291,21 +291,18 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
             );
         }
 
-        let (alloc_kind, mut alloc) = match self.alloc_map.remove(&alloc_id) {
-            Some(alloc) => alloc,
-            None => {
-                // Deallocating global memory -- always an error
-                return Err(match self.tcx.get_global_alloc(alloc_id) {
-                    Some(GlobalAlloc::Function(..)) => {
-                        err_ub_format!("deallocating {}, which is a function", alloc_id)
-                    }
-                    Some(GlobalAlloc::Static(..) | GlobalAlloc::Memory(..)) => {
-                        err_ub_format!("deallocating {}, which is static memory", alloc_id)
-                    }
-                    None => err_ub!(PointerUseAfterFree(alloc_id)),
+        let Some((alloc_kind, mut alloc)) = self.alloc_map.remove(&alloc_id) else {
+            // Deallocating global memory -- always an error
+            return Err(match self.tcx.get_global_alloc(alloc_id) {
+                Some(GlobalAlloc::Function(..)) => {
+                    err_ub_format!("deallocating {}, which is a function", alloc_id)
                 }
-                .into());
+                Some(GlobalAlloc::Static(..) | GlobalAlloc::Memory(..)) => {
+                    err_ub_format!("deallocating {}, which is static memory", alloc_id)
+                }
+                None => err_ub!(PointerUseAfterFree(alloc_id)),
             }
+            .into());
         };
 
         if alloc.mutability == Mutability::Not {
@@ -957,9 +954,9 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
         ptr: Pointer<Option<M::PointerTag>>,
         size: Size,
     ) -> InterpResult<'tcx, &[u8]> {
-        let alloc_ref = match self.get(ptr, size, Align::ONE)? {
-            Some(a) => a,
-            None => return Ok(&[]), // zero-sized access
+        let Some(alloc_ref) = self.get(ptr, size, Align::ONE)? else {
+            // zero-sized access
+            return Ok(&[]);
         };
         // Side-step AllocRef and directly access the underlying bytes more efficiently.
         // (We are staying inside the bounds here so all is good.)
@@ -983,17 +980,14 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
         assert_eq!(lower, len, "can only write iterators with a precise length");
 
         let size = Size::from_bytes(len);
-        let alloc_ref = match self.get_mut(ptr, size, Align::ONE)? {
-            Some(alloc_ref) => alloc_ref,
-            None => {
-                // zero-sized access
-                assert_matches!(
-                    src.next(),
-                    None,
-                    "iterator said it was empty but returned an element"
-                );
-                return Ok(());
-            }
+        let Some(alloc_ref) = self.get_mut(ptr, size, Align::ONE)? else {
+            // zero-sized access
+            assert_matches!(
+                src.next(),
+                None,
+                "iterator said it was empty but returned an element"
+            );
+            return Ok(());
         };
 
         // Side-step AllocRef and directly access the underlying bytes more efficiently.
@@ -1043,18 +1037,18 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
         // and once below to get the underlying `&[mut] Allocation`.
 
         // Source alloc preparations and access hooks.
-        let (src_alloc_id, src_offset, src) = match src_parts {
-            None => return Ok(()), // Zero-sized *source*, that means dst is also zero-sized and we have nothing to do.
-            Some(src_ptr) => src_ptr,
+        let Some((src_alloc_id, src_offset, src)) = src_parts else {
+            // Zero-sized *source*, that means dst is also zero-sized and we have nothing to do.
+            return Ok(());
         };
         let src_alloc = self.get_raw(src_alloc_id)?;
         let src_range = alloc_range(src_offset, size);
         M::memory_read(&self.extra, &src_alloc.extra, src.provenance, src_range)?;
         // We need the `dest` ptr for the next operation, so we get it now.
         // We already did the source checks and called the hooks so we are good to return early.
-        let (dest_alloc_id, dest_offset, dest) = match dest_parts {
-            None => return Ok(()), // Zero-sized *destiantion*.
-            Some(dest_ptr) => dest_ptr,
+        let Some((dest_alloc_id, dest_offset, dest)) = dest_parts else {
+            // Zero-sized *destination*.
+            return Ok(());
         };
 
         // This checks relocation edges on the src, which needs to happen before

compiler/rustc_const_eval/src/interpret/operand.rs

@@ -258,15 +258,12 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             return Ok(None);
         }
 
-        let alloc = match self.get_alloc(mplace)? {
-            Some(ptr) => ptr,
-            None => {
-                return Ok(Some(ImmTy {
-                    // zero-sized type
-                    imm: Scalar::ZST.into(),
-                    layout: mplace.layout,
-                }));
-            }
+        let Some(alloc) = self.get_alloc(mplace)? else {
+            return Ok(Some(ImmTy {
+                // zero-sized type
+                imm: Scalar::ZST.into(),
+                layout: mplace.layout,
+            }));
         };
 
         match mplace.layout.abi {

compiler/rustc_const_eval/src/interpret/place.rs

@@ -420,9 +420,8 @@ where
     ) -> InterpResult<'tcx, impl Iterator<Item = InterpResult<'tcx, MPlaceTy<'tcx, Tag>>> + 'a>
     {
         let len = base.len(self)?; // also asserts that we have a type where this makes sense
-        let stride = match base.layout.fields {
-            FieldsShape::Array { stride, .. } => stride,
-            _ => span_bug!(self.cur_span(), "mplace_array_fields: expected an array layout"),
+        let FieldsShape::Array { stride, .. } = base.layout.fields else {
+            span_bug!(self.cur_span(), "mplace_array_fields: expected an array layout");
         };
         let layout = base.layout.field(self, 0);
         let dl = &self.tcx.data_layout;
@@ -747,9 +746,9 @@ where
 
         // Invalid places are a thing: the return place of a diverging function
         let tcx = *self.tcx;
-        let mut alloc = match self.get_alloc_mut(dest)? {
-            Some(a) => a,
-            None => return Ok(()), // zero-sized access
+        let Some(mut alloc) = self.get_alloc_mut(dest)? else {
+            // zero-sized access
+            return Ok(());
         };
 
         // FIXME: We should check that there are dest.layout.size many bytes available in

compiler/rustc_const_eval/src/interpret/step.rs

@@ -46,15 +46,12 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             return Ok(false);
         }
 
-        let loc = match self.frame().loc {
-            Ok(loc) => loc,
-            Err(_) => {
-                // We are unwinding and this fn has no cleanup code.
-                // Just go on unwinding.
-                trace!("unwinding: skipping frame");
-                self.pop_stack_frame(/* unwinding */ true)?;
-                return Ok(true);
-            }
+        let Ok(loc) = self.frame().loc else {
+            // We are unwinding and this fn has no cleanup code.
+            // Just go on unwinding.
+            trace!("unwinding: skipping frame");
+            self.pop_stack_frame(/* unwinding */ true)?;
+            return Ok(true);
         };
         let basic_block = &self.body().basic_blocks()[loc.block];
 

compiler/rustc_const_eval/src/interpret/terminator.rs

@@ -321,10 +321,9 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             | ty::InstanceDef::CloneShim(..)
             | ty::InstanceDef::Item(_) => {
                 // We need MIR for this fn
-                let (body, instance) =
-                    match M::find_mir_or_eval_fn(self, instance, caller_abi, args, ret, unwind)? {
-                        Some(body) => body,
-                        None => return Ok(()),
+                let Some((body, instance)) =
+                    M::find_mir_or_eval_fn(self, instance, caller_abi, args, ret, unwind)? else {
+                        return Ok(());
                     };
 
                 // Compute callee information using the `instance` returned by

compiler/rustc_const_eval/src/interpret/validity.rs

@@ -851,12 +851,9 @@ impl<'rt, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValueVisitor<'mir, 'tcx, M>
                 // to reject those pointers, we just do not have the machinery to
                 // talk about parts of a pointer.
                 // We also accept uninit, for consistency with the slow path.
-                let alloc = match self.ecx.memory.get(mplace.ptr, size, mplace.align)? {
-                    Some(a) => a,
-                    None => {
-                        // Size 0, nothing more to check.
-                        return Ok(());
-                    }
+                let Some(alloc) = self.ecx.memory.get(mplace.ptr, size, mplace.align)? else {
+                    // Size 0, nothing more to check.
+                    return Ok(());
                 };
 
                 let allow_uninit_and_ptr = !M::enforce_number_validity(self.ecx);

compiler/rustc_const_eval/src/transform/check_consts/check.rs

@@ -134,11 +134,8 @@ impl<'mir, 'tcx> Qualifs<'mir, 'tcx> {
             .find(|(_, block)| matches!(block.terminator().kind, TerminatorKind::Return))
             .map(|(bb, _)| bb);
 
-        let return_block = match return_block {
-            None => {
-                return qualifs::in_any_value_of_ty(ccx, ccx.body.return_ty(), tainted_by_errors);
-            }
-            Some(bb) => bb,
+        let Some(return_block) = return_block else {
+            return qualifs::in_any_value_of_ty(ccx, ccx.body.return_ty(), tainted_by_errors);
         };
 
         let return_loc = ccx.body.terminator_loc(return_block);

compiler/rustc_const_eval/src/transform/promote_consts.rs

@@ -747,15 +747,12 @@ impl<'a, 'tcx> Promoter<'a, 'tcx> {
         if loc.statement_index < num_stmts {
             let (mut rvalue, source_info) = {
                 let statement = &mut self.source[loc.block].statements[loc.statement_index];
-                let rhs = match statement.kind {
-                    StatementKind::Assign(box (_, ref mut rhs)) => rhs,
-                    _ => {
-                        span_bug!(
-                            statement.source_info.span,
-                            "{:?} is not an assignment",
-                            statement
-                        );
-                    }
+                let StatementKind::Assign(box (_, ref mut rhs)) = statement.kind else {
+                    span_bug!(
+                        statement.source_info.span,
+                        "{:?} is not an assignment",
+                        statement
+                    );
                 };
 
                 (

compiler/rustc_const_eval/src/util/alignment.rs

@@ -15,12 +15,9 @@ where
     L: HasLocalDecls<'tcx>,
 {
     debug!("is_disaligned({:?})", place);
-    let pack = match is_within_packed(tcx, local_decls, place) {
-        None => {
-            debug!("is_disaligned({:?}) - not within packed", place);
-            return false;
-        }
-        Some(pack) => pack,
+    let Some(pack) = is_within_packed(tcx, local_decls, place) else {
+        debug!("is_disaligned({:?}) - not within packed", place);
+        return false;
     };
 
     let ty = place.ty(local_decls, tcx).ty;