Auto merge of #69678 - Dylan-DPC:rollup-yoaueud, r=Dylan-DPC

Rollup of 6 pull requests

Successful merges:

 - #69565 (miri engine: turn some debug_assert into assert)
 - #69621 (use question mark operator in a few places.)
 - #69650 (cleanup more iterator usages (and other things))
 - #69653 (use conditions directly)
 - #69665 (Invoke OptimizerLastEPCallbacks in PreLinkThinLTO)
 - #69670 (Add explanation for E0379)

Failed merges:

r? @ghost

Author: bors

src/liballoc/collections/btree/node.rs

@@ -1191,7 +1191,7 @@ impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::
         let right_len = right_node.len();
 
         // necessary for correctness, but in a private module
-        assert!(left_len + right_len + 1 <= CAPACITY);
+        assert!(left_len + right_len < CAPACITY);
 
         unsafe {
             ptr::write(

src/libcore/iter/adapters/mod.rs

@@ -1894,9 +1894,7 @@ where
             let to_skip = self.n;
             self.n = 0;
             // nth(n) skips n+1
-            if self.iter.nth(to_skip - 1).is_none() {
-                return None;
-            }
+            self.iter.nth(to_skip - 1)?;
         }
         self.iter.nth(n)
     }
@@ -1916,9 +1914,7 @@ where
     fn last(mut self) -> Option<I::Item> {
         if self.n > 0 {
             // nth(n) skips n+1
-            if self.iter.nth(self.n - 1).is_none() {
-                return None;
-            }
+            self.iter.nth(self.n - 1)?;
         }
         self.iter.last()
     }

src/librustc/hir/map/mod.rs

@@ -338,9 +338,8 @@ impl<'hir> Map<'hir> {
             Node::Variant(_) => DefKind::Variant,
             Node::Ctor(variant_data) => {
                 // FIXME(eddyb) is this even possible, if we have a `Node::Ctor`?
-                if variant_data.ctor_hir_id().is_none() {
-                    return None;
-                }
+                variant_data.ctor_hir_id()?;
+
                 let ctor_of = match self.find(self.get_parent_node(hir_id)) {
                     Some(Node::Item(..)) => def::CtorOf::Struct,
                     Some(Node::Variant(..)) => def::CtorOf::Variant,

src/librustc/mir/mod.rs

@@ -189,7 +189,7 @@ impl<'tcx> Body<'tcx> {
     ) -> Self {
         // We need `arg_count` locals, and one for the return place.
         assert!(
-            local_decls.len() >= arg_count + 1,
+            local_decls.len() > arg_count,
             "expected at least {} locals, got {}",
             arg_count + 1,
             local_decls.len()

src/librustc/ty/instance.rs

@@ -115,9 +115,7 @@ impl<'tcx> Instance<'tcx> {
         }
 
         // If this a non-generic instance, it cannot be a shared monomorphization.
-        if self.substs.non_erasable_generics().next().is_none() {
-            return None;
-        }
+        self.substs.non_erasable_generics().next()?;
 
         match self.def {
             InstanceDef::Item(def_id) => tcx

src/librustc_codegen_llvm/va_arg.rs

@@ -117,8 +117,7 @@ pub(super) fn emit_va_arg(
         // Windows x86_64
         ("x86_64", true) => {
             let target_ty_size = bx.cx.size_of(target_ty).bytes();
-            let indirect =
-                if target_ty_size > 8 || !target_ty_size.is_power_of_two() { true } else { false };
+            let indirect: bool = target_ty_size > 8 || !target_ty_size.is_power_of_two();
             emit_ptr_va_arg(bx, addr, target_ty, indirect, Align::from_bytes(8).unwrap(), false)
         }
         // For all other architecture/OS combinations fall back to using

src/librustc_codegen_ssa/back/link.rs

@@ -186,7 +186,7 @@ pub fn get_linker(sess: &Session, linker: &Path, flavor: LinkerFlavor) -> (PathB
     if flavor == LinkerFlavor::Msvc && t.target_vendor == "uwp" {
         if let Some(ref tool) = msvc_tool {
             let original_path = tool.path();
-            if let Some(ref root_lib_path) = original_path.ancestors().skip(4).next() {
+            if let Some(ref root_lib_path) = original_path.ancestors().nth(4) {
                 let arch = match t.arch.as_str() {
                     "x86_64" => Some("x64".to_string()),
                     "x86" => Some("x86".to_string()),

src/librustc_error_codes/error_codes/E0379.md

@@ -1,3 +1,15 @@
+A trait method was declared const.
+
+Erroneous code example:
+
+```compile_fail,E0379
+#![feature(const_fn)]
+
+trait Foo {
+    const fn bar() -> u32; // error!
+}
+```
+
 Trait methods cannot be declared `const` by design. For more information, see
 [RFC 911].
 

src/librustc_expand/mbe/transcribe.rs

@@ -119,9 +119,9 @@ pub(super) fn transcribe(
         let tree = if let Some(tree) = stack.last_mut().unwrap().next() {
             // If it still has a TokenTree we have not looked at yet, use that tree.
             tree
-        }
-        // The else-case never produces a value for `tree` (it `continue`s or `return`s).
-        else {
+        } else {
+            // This else-case never produces a value for `tree` (it `continue`s or `return`s).
+
             // Otherwise, if we have just reached the end of a sequence and we can keep repeating,
             // go back to the beginning of the sequence.
             if let Frame::Sequence { idx, sep, .. } = stack.last_mut().unwrap() {

src/librustc_incremental/persist/work_product.rs

@@ -13,9 +13,7 @@ pub fn copy_cgu_workproducts_to_incr_comp_cache_dir(
     files: &[(WorkProductFileKind, PathBuf)],
 ) -> Option<(WorkProductId, WorkProduct)> {
     debug!("copy_cgu_workproducts_to_incr_comp_cache_dir({:?},{:?})", cgu_name, files);
-    if sess.opts.incremental.is_none() {
-        return None;
-    }
+    sess.opts.incremental.as_ref()?;
 
     let saved_files = files
         .iter()