Auto merge of #76975 - RalfJung:rollup-s2wiuqr, r=RalfJung

Rollup of 15 pull requests

Successful merges:

 - #76732 (Add docs for `BasicBlock`)
 - #76832 (Let backends define custom targets)
 - #76866 (Remove unused feature gates from library/ crates)
 - #76875 (Move to intra-doc links in library/alloc/src/collections/binary_heap.rs)
 - #76876 (Move to intra-doc links in collections/btree/map.rs and collections/linked_list.rs)
 - #76877 (Move to intra-doc links in collections/vec_deque.rs and collections/vec_deque/drain.rs)
 - #76878 (Move the version number to a plaintext file)
 - #76883 (README.md: Remove prompts from code blocks)
 - #76887 (Add missing examples on HashSet iter types)
 - #76890 (use matches!() macro for simple if let conditions)
 - #76891 (don't take `TyCtxt` by reference)
 - #76910 (transmute: use diagnostic item)
 - #76924 (Add tracking issue for feature(unix_socket_peek))
 - #76926 (BTreeMap: code readability tweaks)
 - #76940 (Don't allow implementing trait directly on type-alias-impl-trait)

Failed merges:

r? `@ghost`

README.md

@@ -44,8 +44,8 @@ by running `./x.py --help` or reading the [rustc dev guide][rustcguidebuild].
 2. Clone the [source] with `git`:
 
    ```sh
-   $ git clone https://github.com/rust-lang/rust.git
-   $ cd rust
+   git clone https://github.com/rust-lang/rust.git
+   cd rust
    ```
 
 [source]: https://github.com/rust-lang/rust
@@ -57,7 +57,7 @@ by running `./x.py --help` or reading the [rustc dev guide][rustcguidebuild].
     Copy the default `config.toml.example` to `config.toml` to get started.
 
     ```sh
-    $ cp config.toml.example config.toml
+    cp config.toml.example config.toml
     ```
 
     If you plan to use `x.py install` to create an installation, it is recommended
@@ -68,7 +68,7 @@ by running `./x.py --help` or reading the [rustc dev guide][rustcguidebuild].
 4. Build and install:
 
     ```sh
-    $ ./x.py build && ./x.py install
+    ./x.py build && ./x.py install
     ```
 
     When complete, `./x.py install` will place several programs into
@@ -106,15 +106,15 @@ build.
 
    ```sh
    # Update package mirrors (may be needed if you have a fresh install of MSYS2)
-   $ pacman -Sy pacman-mirrors
+   pacman -Sy pacman-mirrors
 
    # Install build tools needed for Rust. If you're building a 32-bit compiler,
    # then replace "x86_64" below with "i686". If you've already got git, python,
    # or CMake installed and in PATH you can remove them from this list. Note
    # that it is important that you do **not** use the 'python2', 'cmake' and 'ninja'
    # packages from the 'msys2' subsystem. The build has historically been known
    # to fail with these packages.
-   $ pacman -S git \
+   pacman -S git \
                make \
                diffutils \
                tar \
@@ -127,7 +127,7 @@ build.
 4. Navigate to Rust's source code (or clone it), then build it:
 
    ```sh
-   $ ./x.py build && ./x.py install
+   ./x.py build && ./x.py install
    ```
 
 #### MSVC
@@ -145,7 +145,7 @@ With these dependencies installed, you can build the compiler in a `cmd.exe`
 shell with:
 
 ```sh
-> python x.py build
+python x.py build
 ```
 
 Currently, building Rust only works with some known versions of Visual Studio. If
@@ -154,8 +154,8 @@ you may need to force rustbuild to use an older version. This can be done
 by manually calling the appropriate vcvars file before running the bootstrap.
 
 ```batch
-> CALL "C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Auxiliary\Build\vcvars64.bat"
-> python x.py build
+CALL "C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Auxiliary\Build\vcvars64.bat"
+python x.py build
 ```
 
 #### Specifying an ABI
@@ -181,8 +181,8 @@ While it's not the recommended build system, this project also provides a
 configure script and makefile (the latter of which just invokes `x.py`).
 
 ```sh
-$ ./configure
-$ make && sudo make install
+./configure
+make && sudo make install
 ```
 
 When using the configure script, the generated `config.mk` file may override the
@@ -194,7 +194,7 @@ When using the configure script, the generated `config.mk` file may override the
 If you’d like to build the documentation, it’s almost the same:
 
 ```sh
-$ ./x.py doc
+./x.py doc
 ```
 
 The generated documentation will appear under `doc` in the `build` directory for

compiler/rustc_ast/src/ast.rs

@@ -1931,7 +1931,7 @@ pub enum TyKind {
 
 impl TyKind {
     pub fn is_implicit_self(&self) -> bool {
-        if let TyKind::ImplicitSelf = *self { true } else { false }
+        matches!(self, TyKind::ImplicitSelf)
     }
 
     pub fn is_unit(&self) -> bool {
@@ -2227,7 +2227,7 @@ pub enum Async {
 
 impl Async {
     pub fn is_async(self) -> bool {
-        if let Async::Yes { .. } = self { true } else { false }
+        matches!(self, Async::Yes { .. })
     }
 
     /// In this case this is an `async` return, the `NodeId` for the generated `impl Trait` item.
@@ -2508,7 +2508,7 @@ pub enum VisibilityKind {
 
 impl VisibilityKind {
     pub fn is_pub(&self) -> bool {
-        if let VisibilityKind::Public = *self { true } else { false }
+        matches!(self, VisibilityKind::Public)
     }
 }
 

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -868,10 +868,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
                     .emit();
                 }
 
-                if !bounds
-                    .iter()
-                    .any(|b| if let GenericBound::Trait(..) = *b { true } else { false })
-                {
+                if !bounds.iter().any(|b| matches!(b, GenericBound::Trait(..))) {
                     self.err_handler().span_err(ty.span, "at least one trait must be specified");
                 }
 

compiler/rustc_attr/src/builtin.rs

@@ -160,10 +160,10 @@ pub enum StabilityLevel {
 
 impl StabilityLevel {
     pub fn is_unstable(&self) -> bool {
-        if let StabilityLevel::Unstable { .. } = *self { true } else { false }
+        matches!(self, StabilityLevel::Unstable { .. })
     }
     pub fn is_stable(&self) -> bool {
-        if let StabilityLevel::Stable { .. } = *self { true } else { false }
+        matches!(self, StabilityLevel::Stable { .. })
     }
 }
 

compiler/rustc_builtin_macros/src/deriving/generic/mod.rs

@@ -1529,7 +1529,7 @@ impl<'a> TraitDef<'a> {
             }
         }
 
-        let is_tuple = if let ast::VariantData::Tuple(..) = struct_def { true } else { false };
+        let is_tuple = matches!(struct_def, ast::VariantData::Tuple(..));
         match (just_spans.is_empty(), named_idents.is_empty()) {
             (false, false) => cx.span_bug(
                 self.span,

compiler/rustc_codegen_ssa/src/traits/backend.rs

@@ -15,6 +15,7 @@ use rustc_session::{
 };
 use rustc_span::symbol::Symbol;
 use rustc_target::abi::LayoutOf;
+use rustc_target::spec::Target;
 
 pub use rustc_data_structures::sync::MetadataRef;
 
@@ -54,6 +55,12 @@ pub trait CodegenBackend {
     fn print_passes(&self) {}
     fn print_version(&self) {}
 
+    /// If this plugin provides additional builtin targets, provide the one enabled by the options here.
+    /// Be careful: this is called *before* init() is called.
+    fn target_override(&self, _opts: &config::Options) -> Option<Target> {
+        None
+    }
+
     fn metadata_loader(&self) -> Box<MetadataLoaderDyn>;
     fn provide(&self, _providers: &mut Providers);
     fn provide_extern(&self, _providers: &mut Providers);

compiler/rustc_errors/src/snippet.rs

@@ -118,17 +118,15 @@ pub struct Annotation {
 impl Annotation {
     /// Whether this annotation is a vertical line placeholder.
     pub fn is_line(&self) -> bool {
-        if let AnnotationType::MultilineLine(_) = self.annotation_type { true } else { false }
+        matches!(self.annotation_type, AnnotationType::MultilineLine(_))
     }
 
     pub fn is_multiline(&self) -> bool {
-        match self.annotation_type {
+        matches!(self.annotation_type,
             AnnotationType::Multiline(_)
             | AnnotationType::MultilineStart(_)
             | AnnotationType::MultilineLine(_)
-            | AnnotationType::MultilineEnd(_) => true,
-            _ => false,
-        }
+            | AnnotationType::MultilineEnd(_))
     }
 
     pub fn len(&self) -> usize {

compiler/rustc_interface/src/tests.rs

@@ -40,6 +40,7 @@ fn mk_session(matches: getopts::Matches) -> (Session, CfgSpecs) {
         DiagnosticOutput::Default,
         Default::default(),
         None,
+        None,
     );
     (sess, cfg)
 }

compiler/rustc_interface/src/util.rs

@@ -65,16 +65,21 @@ pub fn create_session(
     lint_caps: FxHashMap<lint::LintId, lint::Level>,
     descriptions: Registry,
 ) -> (Lrc<Session>, Lrc<Box<dyn CodegenBackend>>) {
+    let codegen_backend = get_codegen_backend(&sopts);
+    // target_override is documented to be called before init(), so this is okay
+    let target_override = codegen_backend.target_override(&sopts);
+
     let mut sess = session::build_session(
         sopts,
         input_path,
         descriptions,
         diagnostic_output,
         lint_caps,
         file_loader,
+        target_override,
     );
 
-    let codegen_backend = get_codegen_backend(&sess);
+    codegen_backend.init(&sess);
 
     let mut cfg = config::build_configuration(&sess, config::to_crate_config(cfg));
     add_configuration(&mut cfg, &mut sess, &*codegen_backend);
@@ -219,13 +224,13 @@ fn load_backend_from_dylib(path: &Path) -> fn() -> Box<dyn CodegenBackend> {
     }
 }
 
-pub fn get_codegen_backend(sess: &Session) -> Box<dyn CodegenBackend> {
+pub fn get_codegen_backend(sopts: &config::Options) -> Box<dyn CodegenBackend> {
     static INIT: Once = Once::new();
 
     static mut LOAD: fn() -> Box<dyn CodegenBackend> = || unreachable!();
 
     INIT.call_once(|| {
-        let codegen_name = sess.opts.debugging_opts.codegen_backend.as_deref().unwrap_or("llvm");
+        let codegen_name = sopts.debugging_opts.codegen_backend.as_deref().unwrap_or("llvm");
         let backend = match codegen_name {
             filename if filename.contains('.') => load_backend_from_dylib(filename.as_ref()),
             codegen_name => get_builtin_codegen_backend(codegen_name),
@@ -235,9 +240,7 @@ pub fn get_codegen_backend(sess: &Session) -> Box<dyn CodegenBackend> {
             LOAD = backend;
         }
     });
-    let backend = unsafe { LOAD() };
-    backend.init(sess);
-    backend
+    unsafe { LOAD() }
 }
 
 // This is used for rustdoc, but it uses similar machinery to codegen backend

compiler/rustc_lint/src/builtin.rs

@@ -1984,9 +1984,9 @@ impl ExplicitOutlivesRequirements {
             .filter_map(|(i, bound)| {
                 if let hir::GenericBound::Outlives(lifetime) = bound {
                     let is_inferred = match tcx.named_region(lifetime.hir_id) {
-                        Some(Region::Static) if infer_static => inferred_outlives
-                            .iter()
-                            .any(|r| if let ty::ReStatic = r { true } else { false }),
+                        Some(Region::Static) if infer_static => {
+                            inferred_outlives.iter().any(|r| matches!(r, ty::ReStatic))
+                        }
                         Some(Region::EarlyBound(index, ..)) => inferred_outlives.iter().any(|r| {
                             if let ty::ReEarlyBound(ebr) = r { ebr.index == index } else { false }
                         }),
@@ -2078,9 +2078,10 @@ impl<'tcx> LateLintPass<'tcx> for ExplicitOutlivesRequirements {
             let mut lint_spans = Vec::new();
 
             for param in hir_generics.params {
-                let has_lifetime_bounds = param.bounds.iter().any(|bound| {
-                    if let hir::GenericBound::Outlives(_) = bound { true } else { false }
-                });
+                let has_lifetime_bounds = param
+                    .bounds
+                    .iter()
+                    .any(|bound| matches!(bound, hir::GenericBound::Outlives(_)));
                 if !has_lifetime_bounds {
                     continue;
                 }
@@ -2349,13 +2350,6 @@ impl<'tcx> LateLintPass<'tcx> for InvalidValue {
 
         /// Determine if this expression is a "dangerous initialization".
         fn is_dangerous_init(cx: &LateContext<'_>, expr: &hir::Expr<'_>) -> Option<InitKind> {
-            // `transmute` is inside an anonymous module (the `extern` block?);
-            // `Invalid` represents the empty string and matches that.
-            // FIXME(#66075): use diagnostic items.  Somehow, that does not seem to work
-            // on intrinsics right now.
-            const TRANSMUTE_PATH: &[Symbol] =
-                &[sym::core, sym::intrinsics, kw::Invalid, sym::transmute];
-
             if let hir::ExprKind::Call(ref path_expr, ref args) = expr.kind {
                 // Find calls to `mem::{uninitialized,zeroed}` methods.
                 if let hir::ExprKind::Path(ref qpath) = path_expr.kind {
@@ -2365,7 +2359,7 @@ impl<'tcx> LateLintPass<'tcx> for InvalidValue {
                         return Some(InitKind::Zeroed);
                     } else if cx.tcx.is_diagnostic_item(sym::mem_uninitialized, def_id) {
                         return Some(InitKind::Uninit);
-                    } else if cx.match_def_path(def_id, TRANSMUTE_PATH) {
+                    } else if cx.tcx.is_diagnostic_item(sym::transmute, def_id) {
                         if is_zero(&args[0]) {
                             return Some(InitKind::Zeroed);
                         }

compiler/rustc_lint/src/context.rs

@@ -720,6 +720,10 @@ impl<'tcx> LateContext<'tcx> {
     /// Anonymous scopes such as `extern` imports are matched with `kw::Invalid`;
     /// inherent `impl` blocks are matched with the name of the type.
     ///
+    /// Instead of using this method, it is often preferable to instead use
+    /// `rustc_diagnostic_item` or a `lang_item`. This is less prone to errors
+    /// as paths get invalidated if the target definition moves.
+    ///
     /// # Examples
     ///
     /// ```rust,ignore (no context or def id available)

compiler/rustc_middle/src/middle/cstore.rs

@@ -69,7 +69,7 @@ pub enum LibSource {
 
 impl LibSource {
     pub fn is_some(&self) -> bool {
-        if let LibSource::Some(_) = *self { true } else { false }
+        matches!(self, LibSource::Some(_))
     }
 
     pub fn option(&self) -> Option<PathBuf> {

compiler/rustc_middle/src/middle/lang_items.rs

@@ -17,7 +17,7 @@ use rustc_target::spec::PanicStrategy;
 impl<'tcx> TyCtxt<'tcx> {
     /// Returns the `DefId` for a given `LangItem`.
     /// If not found, fatally aborts compilation.
-    pub fn require_lang_item(&self, lang_item: LangItem, span: Option<Span>) -> DefId {
+    pub fn require_lang_item(self, lang_item: LangItem, span: Option<Span>) -> DefId {
         self.lang_items().require(lang_item).unwrap_or_else(|msg| {
             if let Some(span) = span {
                 self.sess.span_fatal(span, &msg)
@@ -27,7 +27,7 @@ impl<'tcx> TyCtxt<'tcx> {
         })
     }
 
-    pub fn fn_trait_kind_from_lang_item(&self, id: DefId) -> Option<ty::ClosureKind> {
+    pub fn fn_trait_kind_from_lang_item(self, id: DefId) -> Option<ty::ClosureKind> {
         let items = self.lang_items();
         match Some(id) {
             x if x == items.fn_trait() => Some(ty::ClosureKind::Fn),
@@ -37,7 +37,7 @@ impl<'tcx> TyCtxt<'tcx> {
         }
     }
 
-    pub fn is_weak_lang_item(&self, item_def_id: DefId) -> bool {
+    pub fn is_weak_lang_item(self, item_def_id: DefId) -> bool {
         self.lang_items().is_weak_lang_item(item_def_id)
     }
 }