Auto merge of #69062 - Dylan-DPC:rollup-7wpjpqu, r=Dylan-DPC

Rollup of 8 pull requests

Successful merges:

 - #66498 (Remove unused feature gates)
 - #68816 (Tweak borrow error on `FnMut` when `Fn` is expected)
 - #68824 (Enable Control Flow Guard in rustbuild)
 - #69022 (traits: preallocate 2 Vecs of known initial size)
 - #69031 (Use `dyn Trait` more in tests)
 - #69044 (Don't run coherence twice for future-compat lints)
 - #69047 (Don't rustfmt check the vendor directory.)
 - #69055 (Clean up E0307 explanation)

Failed merges:

r? @ghost

Author: bors

config.toml.example

@@ -444,6 +444,10 @@
 # Use LLVM libunwind as the implementation for Rust's unwinder.
 #llvm-libunwind = false
 
+# Enable Windows Control Flow Guard checks in the standard library.
+# This only applies from stage 1 onwards, and only for Windows targets.
+#control-flow-guard = false
+
 # =============================================================================
 # Options for specific targets
 #

rustfmt.toml

@@ -7,6 +7,7 @@ merge_derives = false
 # tidy only checks files which are not ignored, each entry follows gitignore style
 ignore = [
     "build",
+    "/vendor/",
 
     # tests for now are not formatted, as they are sometimes pretty-printing constrained
     # (and generally rustfmt can move around comments in UI-testing incompatible ways)

src/bootstrap/builder.rs

@@ -1135,6 +1135,20 @@ impl<'a> Builder<'a> {
             );
         }
 
+        // If Control Flow Guard is enabled, pass the `control_flow_guard=checks` flag to rustc
+        // when compiling the standard library, since this might be linked into the final outputs
+        // produced by rustc. Since this mitigation is only available on Windows, only enable it
+        // for the standard library in case the compiler is run on a non-Windows platform.
+        // This is not needed for stage 0 artifacts because these will only be used for building
+        // the stage 1 compiler.
+        if cfg!(windows)
+            && mode == Mode::Std
+            && self.config.control_flow_guard
+            && compiler.stage >= 1
+        {
+            rustflags.arg("-Zcontrol_flow_guard=checks");
+        }
+
         // For `cargo doc` invocations, make rustdoc print the Rust version into the docs
         cargo.env("RUSTDOC_CRATE_VERSION", self.rust_version());
 

src/bootstrap/config.rs

@@ -116,6 +116,7 @@ pub struct Config {
     pub targets: Vec<Interned<String>>,
     pub local_rebuild: bool,
     pub jemalloc: bool,
+    pub control_flow_guard: bool,
 
     // dist misc
     pub dist_sign_folder: Option<PathBuf>,
@@ -333,6 +334,7 @@ struct Rust {
     jemalloc: Option<bool>,
     test_compare_mode: Option<bool>,
     llvm_libunwind: Option<bool>,
+    control_flow_guard: Option<bool>,
 }
 
 /// TOML representation of how each build target is configured.
@@ -580,6 +582,7 @@ impl Config {
             set(&mut config.rust_verify_llvm_ir, rust.verify_llvm_ir);
             config.rust_thin_lto_import_instr_limit = rust.thin_lto_import_instr_limit;
             set(&mut config.rust_remap_debuginfo, rust.remap_debuginfo);
+            set(&mut config.control_flow_guard, rust.control_flow_guard);
 
             if let Some(ref backends) = rust.codegen_backends {
                 config.rust_codegen_backends =

src/bootstrap/configure.py

@@ -60,6 +60,7 @@ def v(*args):
 o("lldb", "rust.lldb", "build lldb")
 o("missing-tools", "dist.missing-tools", "allow failures when building tools")
 o("use-libcxx", "llvm.use-libcxx", "build LLVM with libc++")
+o("control-flow-guard", "rust.control-flow-guard", "Enable Control Flow Guard")
 
 o("cflags", "llvm.cflags", "build LLVM with these extra compiler flags")
 o("cxxflags", "llvm.cxxflags", "build LLVM with these extra compiler flags")

src/bootstrap/lib.rs

@@ -103,7 +103,6 @@
 //! More documentation can be found in each respective module below, and you can
 //! also check out the `src/bootstrap/README.md` file for more information.
 
-#![feature(core_intrinsics)]
 #![feature(drain_filter)]
 
 use std::cell::{Cell, RefCell};

src/doc/unstable-book/src/compiler-flags/control-flow-guard.md

@@ -0,0 +1,34 @@
+# `control_flow_guard`
+
+The tracking issue for this feature is: [#68793](https://github.com/rust-lang/rust/issues/68793).
+
+------------------------
+
+The `-Zcontrol_flow_guard=checks` compiler flag enables the Windows [Control Flow Guard][cfguard-docs] platform security feature. When enabled, the compiler outputs a list of valid indirect call targets, and inserts runtime checks on all indirect jump instructions to ensure that the destination is in the list of valid call targets.
+
+[cfguard-docs]: https://docs.microsoft.com/en-us/windows/win32/secbp/control-flow-guard
+
+For testing purposes, the `-Zcontrol_flow_guard=nochecks` compiler flag can be used to emit only the list of valid call targets, but not the runtime checks.
+
+It is strongly recommended to also enable Control Flow Guard checks in all linked libraries, including the standard library. 
+
+To enable Control Flow Guard in the standard library, you can use the [cargo `-Zbuild-std` functionality][build-std] to recompile the standard library with the same configuration options as the main program. 
+
+[build-std]: https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#build-std
+
+For example:
+```cmd
+rustup toolchain install --force nightly
+rustup component add rust-src
+SET RUSTFLAGS=-Zcontrol_flow_guard=checks
+cargo +nightly build -Z build-std --target x86_64-pc-windows-msvc
+```
+
+```PowerShell
+rustup toolchain install --force nightly
+rustup component add rust-src
+$Env:RUSTFLAGS = "-Zcontrol_flow_guard=checks"
+cargo +nightly build -Z build-std --target x86_64-pc-windows-msvc
+```
+
+Alternatively, if you are building the standard library from source, you can set `control-flow-guard = true` in the config.toml file.

src/librustc/lib.rs

@@ -27,7 +27,6 @@
 //! This API is completely unstable and subject to change.
 
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/")]
-#![feature(arbitrary_self_types)]
 #![feature(bool_to_option)]
 #![feature(box_patterns)]
 #![feature(box_syntax)]
@@ -39,21 +38,15 @@
 #![feature(marker_trait_attr)]
 #![feature(extern_types)]
 #![feature(nll)]
-#![feature(optin_builtin_traits)]
 #![feature(option_expect_none)]
 #![feature(range_is_empty)]
 #![feature(specialization)]
-#![feature(unboxed_closures)]
-#![feature(thread_local)]
-#![feature(trace_macros)]
 #![feature(trusted_len)]
 #![feature(vec_remove_item)]
 #![feature(stmt_expr_attributes)]
-#![feature(integer_atomics)]
 #![feature(test)]
 #![feature(in_band_lifetimes)]
 #![feature(crate_visibility_modifier)]
-#![feature(log_syntax)]
 #![feature(associated_type_bounds)]
 #![feature(rustc_attrs)]
 #![feature(hash_raw_entry)]

src/librustc/traits/select.rs

@@ -3472,7 +3472,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         // that order.
         let predicates = tcx.predicates_of(def_id);
         assert_eq!(predicates.parent, None);
-        let mut obligations = Vec::new();
+        let mut obligations = Vec::with_capacity(predicates.predicates.len());
         for (predicate, _) in predicates.predicates {
             let predicate = normalize_with_depth_to(
                 self,

src/librustc/traits/specialize/specialization_graph.rs

@@ -86,10 +86,10 @@ impl<'tcx> Children {
                 impl_def_id, simplified_self, possible_sibling,
             );
 
-            let overlap_error = |overlap: traits::coherence::OverlapResult<'_>| {
-                // Found overlap, but no specialization; error out.
+            let create_overlap_error = |overlap: traits::coherence::OverlapResult<'_>| {
                 let trait_ref = overlap.impl_header.trait_ref.unwrap();
                 let self_ty = trait_ref.self_ty();
+
                 OverlapError {
                     with_impl: possible_sibling,
                     trait_desc: trait_ref.print_only_trait_path().to_string(),
@@ -106,21 +106,49 @@ impl<'tcx> Children {
                 }
             };
 
-            let allowed_to_overlap =
-                tcx.impls_are_allowed_to_overlap(impl_def_id, possible_sibling);
+            let report_overlap_error = |overlap: traits::coherence::OverlapResult<'_>,
+                                        last_lint: &mut _| {
+                // Found overlap, but no specialization; error out or report future-compat warning.
+
+                // Do we *still* get overlap if we disable the future-incompatible modes?
+                let should_err = traits::overlapping_impls(
+                    tcx,
+                    possible_sibling,
+                    impl_def_id,
+                    traits::SkipLeakCheck::default(),
+                    |_| true,
+                    || false,
+                );
+
+                let error = create_overlap_error(overlap);
+
+                if should_err {
+                    Err(error)
+                } else {
+                    *last_lint = Some(FutureCompatOverlapError {
+                        error,
+                        kind: FutureCompatOverlapErrorKind::LeakCheck,
+                    });
+
+                    Ok((false, false))
+                }
+            };
 
+            let last_lint_mut = &mut last_lint;
             let (le, ge) = traits::overlapping_impls(
                 tcx,
                 possible_sibling,
                 impl_def_id,
-                traits::SkipLeakCheck::default(),
+                traits::SkipLeakCheck::Yes,
                 |overlap| {
-                    if let Some(overlap_kind) = &allowed_to_overlap {
+                    if let Some(overlap_kind) =
+                        tcx.impls_are_allowed_to_overlap(impl_def_id, possible_sibling)
+                    {
                         match overlap_kind {
                             ty::ImplOverlapKind::Permitted { marker: _ } => {}
                             ty::ImplOverlapKind::Issue33140 => {
-                                last_lint = Some(FutureCompatOverlapError {
-                                    error: overlap_error(overlap),
+                                *last_lint_mut = Some(FutureCompatOverlapError {
+                                    error: create_overlap_error(overlap),
                                     kind: FutureCompatOverlapErrorKind::Issue33140,
                                 });
                             }
@@ -132,7 +160,11 @@ impl<'tcx> Children {
                     let le = tcx.specializes((impl_def_id, possible_sibling));
                     let ge = tcx.specializes((possible_sibling, impl_def_id));
 
-                    if le == ge { Err(overlap_error(overlap)) } else { Ok((le, ge)) }
+                    if le == ge {
+                        report_overlap_error(overlap, last_lint_mut)
+                    } else {
+                        Ok((le, ge))
+                    }
                 },
                 || Ok((false, false)),
             )?;
@@ -153,27 +185,8 @@ impl<'tcx> Children {
 
                 replace_children.push(possible_sibling);
             } else {
-                if let None = allowed_to_overlap {
-                    // Do future-compat checks for overlap.
-
-                    if last_lint.is_none() {
-                        traits::overlapping_impls(
-                            tcx,
-                            possible_sibling,
-                            impl_def_id,
-                            traits::SkipLeakCheck::Yes,
-                            |overlap| {
-                                last_lint = Some(FutureCompatOverlapError {
-                                    error: overlap_error(overlap),
-                                    kind: FutureCompatOverlapErrorKind::LeakCheck,
-                                });
-                            },
-                            || (),
-                        );
-                    }
-                }
-
-                // no overlap (error bailed already via ?)
+                // Either there's no overlap, or the overlap was already reported by
+                // `overlap_error`.
             }
         }