Auto merge of #129464 - GuillaumeGomez:rollup-ckfqd7h, r=GuillaumeGomez

Rollup of 9 pull requests

Successful merges:

 - #128511 (Document WebAssembly target feature expectations)
 - #129243 (do not build `cargo-miri` by default on stable channel)
 - #129263 (Add a missing compatibility note in the 1.80.0 release notes)
 - #129276 (Stabilize feature `char_indices_offset`)
 - #129350 (adapt integer comparison tests for LLVM 20 IR changes)
 - #129408 (Fix handling of macro arguments within the `dropping_copy_types` lint)
 - #129426 (rustdoc-search: use tighter json for names and parents)
 - #129437 (Fix typo in a help diagnostic)
 - #129457 (kobzol vacation)

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

RELEASES.md

@@ -143,6 +143,8 @@ Compatibility Notes
 - [Turn `proc_macro_back_compat` lint into a hard error.](https://github.com/rust-lang/rust/pull/125596/)
 - [Detect unused structs even when implementing private traits](https://github.com/rust-lang/rust/pull/122382/)
 - [`std::sync::ReentrantLockGuard<T>` is no longer `Sync` if `T: !Sync`](https://github.com/rust-lang/rust/pull/125527) which means [`std::io::StdoutLock` and `std::io::StderrLock` are no longer Sync](https://github.com/rust-lang/rust/issues/127340)
+- [Type inference will fail in some cases due to new implementations of `FromIterator for Box<str>`.](https://github.com/rust-lang/rust/pull/99969/)
+  Notably, this breaks versions of the `time` crate before 0.3.35, due to no longer inferring the implementation for `Box<[_]>`.
 
 <a id="1.80-Internal-Changes"></a>
 

compiler/rustc_lint/src/drop_forget_useless.rs

@@ -151,10 +151,11 @@ impl<'tcx> LateLintPass<'tcx> for DropForgetUseless {
                     && let Node::Stmt(stmt) = node
                     && let StmtKind::Semi(e) = stmt.kind
                     && e.hir_id == expr.hir_id
+                    && let Some(arg_span) = arg.span.find_ancestor_inside(expr.span)
                 {
                     UseLetUnderscoreIgnoreSuggestion::Suggestion {
-                        start_span: expr.span.shrink_to_lo().until(arg.span),
-                        end_span: arg.span.shrink_to_hi().until(expr.span.shrink_to_hi()),
+                        start_span: expr.span.shrink_to_lo().until(arg_span),
+                        end_span: arg_span.shrink_to_hi().until(expr.span.shrink_to_hi()),
                     }
                 } else {
                     UseLetUnderscoreIgnoreSuggestion::Note

compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs

@@ -1693,7 +1693,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                     StringPart::highlighted("multiple different versions".to_string()),
                     StringPart::normal(" of crate `".to_string()),
                     StringPart::highlighted(format!("{name}")),
-                    StringPart::normal("` the your dependency graph".to_string()),
+                    StringPart::normal("` in the dependency graph".to_string()),
                 ],
             );
             let candidates = if impl_candidates.is_empty() {

config.example.toml

@@ -337,6 +337,7 @@
 #    "analysis",
 #    "src",
 #    "wasm-component-ld",
+#    "miri", "cargo-miri" # for dev/nightly channels
 #]
 
 # Verbosity level: 0 == not verbose, 1 == verbose, 2 == very verbose, 3 == print environment variables on each rustc invocation

library/core/src/lib.rs

@@ -110,7 +110,6 @@
 #![cfg_attr(bootstrap, feature(offset_of_nested))]
 #![feature(array_ptr_get)]
 #![feature(asm_experimental_arch)]
-#![feature(char_indices_offset)]
 #![feature(const_align_of_val)]
 #![feature(const_align_of_val_raw)]
 #![feature(const_align_offset)]

library/core/src/str/iter.rs

@@ -241,24 +241,35 @@ impl<'a> CharIndices<'a> {
     /// Returns the byte position of the next character, or the length
     /// of the underlying string if there are no more characters.
     ///
+    /// This means that, when the iterator has not been fully consumed,
+    /// the returned value will match the index that will be returned
+    /// by the next call to [`next()`](Self::next).
+    ///
     /// # Examples
     ///
     /// ```
-    /// #![feature(char_indices_offset)]
     /// let mut chars = "a楽".char_indices();
     ///
+    /// // `next()` has not been called yet, so `offset()` returns the byte
+    /// // index of the first character of the string, which is always 0.
     /// assert_eq!(chars.offset(), 0);
+    /// // As expected, the first call to `next()` also returns 0 as index.
     /// assert_eq!(chars.next(), Some((0, 'a')));
     ///
+    /// // `next()` has been called once, so `offset()` returns the byte index
+    /// // of the second character ...
     /// assert_eq!(chars.offset(), 1);
+    /// // ... which matches the index returned by the next call to `next()`.
     /// assert_eq!(chars.next(), Some((1, '楽')));
     ///
+    /// // Once the iterator has been consumed, `offset()` returns the length
+    /// // in bytes of the string.
     /// assert_eq!(chars.offset(), 4);
     /// assert_eq!(chars.next(), None);
     /// ```
     #[inline]
     #[must_use]
-    #[unstable(feature = "char_indices_offset", issue = "83871")]
+    #[stable(feature = "char_indices_offset", since = "CURRENT_RUSTC_VERSION")]
     pub fn offset(&self) -> usize {
         self.front_offset
     }

src/bootstrap/src/core/build_steps/tool.rs

@@ -1096,7 +1096,7 @@ tool_extended!((self, builder),
     CargoClippy, "src/tools/clippy", "cargo-clippy", stable=true;
     Clippy, "src/tools/clippy", "clippy-driver", stable=true, add_bins_to_sysroot = ["clippy-driver", "cargo-clippy"];
     Miri, "src/tools/miri", "miri", stable=false, add_bins_to_sysroot = ["miri"];
-    CargoMiri, "src/tools/miri/cargo-miri", "cargo-miri", stable=true, add_bins_to_sysroot = ["cargo-miri"];
+    CargoMiri, "src/tools/miri/cargo-miri", "cargo-miri", stable=false, add_bins_to_sysroot = ["cargo-miri"];
     Rls, "src/tools/rls", "rls", stable=true;
     Rustfmt, "src/tools/rustfmt", "rustfmt", stable=true, add_bins_to_sysroot = ["rustfmt", "cargo-fmt"];
 );

src/doc/rustc/src/SUMMARY.md

@@ -81,6 +81,7 @@
     - [wasm32-wasip1](platform-support/wasm32-wasip1.md)
     - [wasm32-wasip1-threads](platform-support/wasm32-wasip1-threads.md)
     - [wasm32-wasip2](platform-support/wasm32-wasip2.md)
+    - [wasm32-unknown-unknown](platform-support/wasm32-unknown-unknown.md)
     - [wasm64-unknown-unknown](platform-support/wasm64-unknown-unknown.md)
     - [\*-win7-windows-msvc](platform-support/win7-windows-msvc.md)
     - [x86_64-fortanix-unknown-sgx](platform-support/x86_64-fortanix-unknown-sgx.md)

src/doc/rustc/src/platform-support.md

@@ -192,7 +192,7 @@ target | std | notes
 [`thumbv8m.main-none-eabi`](platform-support/thumbv8m.main-none-eabi.md) | * | Bare Armv8-M Mainline
 [`thumbv8m.main-none-eabihf`](platform-support/thumbv8m.main-none-eabi.md) | * | Bare Armv8-M Mainline, hardfloat
 `wasm32-unknown-emscripten` | ✓ | WebAssembly via Emscripten
-`wasm32-unknown-unknown` | ✓ | WebAssembly
+[`wasm32-unknown-unknown`](platform-support/wasm32-unknown-unknown.md) | ✓ | WebAssembly
 `wasm32-wasi` | ✓ | WebAssembly with WASI (undergoing a [rename to `wasm32-wasip1`][wasi-rename])
 [`wasm32-wasip1`](platform-support/wasm32-wasip1.md) | ✓ | WebAssembly with WASI
 [`wasm32-wasip1-threads`](platform-support/wasm32-wasip1-threads.md) | ✓ | WebAssembly with WASI Preview 1 and threads

src/doc/rustc/src/platform-support/wasm32-unknown-unknown.md

@@ -0,0 +1,198 @@
+# `wasm32-unknown-unknown`
+
+**Tier: 2**
+
+The `wasm32-unknown-unknown` target is a WebAssembly compilation target which
+does not import any functions from the host for the standard library. This is
+the "minimal" WebAssembly in the sense of making the fewest assumptions about
+the host environment. This target is often used when compiling to the web or
+JavaScript environments as there is no standard for what functions can be
+imported on the web. This target can also be useful for creating minimal or
+bare-bones WebAssembly binaries.
+
+The `wasm32-unknown-unknown` target has support for the Rust standard library
+but many parts of the standard library do not work and return errors. For
+example `println!` does nothing, `std::fs` always return errors, and
+`std::thread::spawn` will panic. There is no means by which this can be
+overridden. For a WebAssembly target that more fully supports the standard
+library see the [`wasm32-wasip1`](./wasm32-wasip1.md) or
+[`wasm32-wasip2`](./wasm32-wasip2.md) targets.
+
+The `wasm32-unknown-unknown` target has full support for the `core` and `alloc`
+crates. It additionally supports the `HashMap` type in the `std` crate, although
+hash maps are not randomized like they are on other platforms.
+
+One existing user of this target (please feel free to edit and expand this list
+too) is the [`wasm-bindgen` project](https://github.com/rustwasm/wasm-bindgen)
+which facilitates Rust code interoperating with JavaScript code. Note, though,
+that not all uses of `wasm32-unknown-unknown` are using JavaScript and the web.
+
+## Target maintainers
+
+When this target was added to the compiler platform-specific documentation here
+was not maintained at that time. This means that the list below is not
+exhaustive and there are more interested parties in this target. That being
+said since when this document was last updated those interested in maintaining
+this target are:
+
+- Alex Crichton, https://github.com/alexcrichton
+
+## Requirements
+
+This target is cross-compiled. The target includes support for `std` itself,
+but as mentioned above many pieces of functionality that require an operating
+system do not work and will return errors.
+
+This target currently has no equivalent in C/C++. There is no C/C++ toolchain
+for this target. While interop is theoretically possible it's recommended to
+instead use one of:
+
+* `wasm32-unknown-emscripten` - for web-based use cases the Emscripten
+  toolchain is typically chosen for running C/C++.
+* [`wasm32-wasip1`](./wasm32-wasip1.md) - the wasi-sdk toolchain is used to
+  compile C/C++ on this target and can interop with Rust code. WASI works on
+  the web so far as there's no blocker, but an implementation of WASI APIs
+  must be either chosen or reimplemented.
+
+This target has no build requirements beyond what's in-tree in the Rust
+repository. Linking binaries requires LLD to be enabled for the `wasm-ld`
+driver. This target uses the `dlmalloc` crate as the default global allocator.
+
+## Building the target
+
+Building this target can be done by:
+
+* Configure the `wasm32-unknown-unknown` target to get built.
+* Configure LLD to be built.
+* Ensure the `WebAssembly` target backend is not disabled in LLVM.
+
+These are all controlled through `config.toml` options. It should be possible
+to build this target on any platform.
+
+## Building Rust programs
+
+Rust programs can be compiled by adding this target via rustup:
+
+```sh
+$ rustup target add wasm32-unknown-unknown
+```
+
+and then compiling with the target:
+
+```sh
+$ rustc foo.rs --target wasm32-unknown-unknown
+$ file foo.wasm
+```
+
+## Cross-compilation
+
+This target can be cross-compiled from any host.
+
+## Testing
+
+This target is not tested in CI for the rust-lang/rust repository. Many tests
+must be disabled to run on this target and failures are non-obvious because
+`println!` doesn't work in the standard library. It's recommended to test the
+`wasm32-wasip1` target instead for WebAssembly compatibility.
+
+## Conditionally compiling code
+
+It's recommended to conditionally compile code for this target with:
+
+```text
+#[cfg(all(target_family = "wasm", target_os = "unknown"))]
+```
+
+Note that there is no way to tell via `#[cfg]` whether code will be running on
+the web or not.
+
+## Enabled WebAssembly features
+
+WebAssembly is an evolving standard which adds new features such as new
+instructions over time. This target's default set of supported WebAssembly
+features will additionally change over time. The `wasm32-unknown-unknown` target
+inherits the default settings of LLVM which typically matches the default
+settings of Emscripten as well.
+
+Changes to WebAssembly go through a [proposals process][proposals] but reaching
+the final stage (stage 5) does not automatically mean that the feature will be
+enabled in LLVM and Rust by default. At this time the general guidance is that
+features must be present in most engines for a "good chunk of time" before
+they're enabled in LLVM by default. There is currently no exact number of
+months or engines that are required to enable features by default.
+
+[proposals]: https://github.com/WebAssembly/proposals
+
+As of the time of this writing the proposals that are enabled by default (the
+`generic` CPU in LLVM terminology) are:
+
+* `multivalue`
+* `mutable-globals`
+* `reference-types`
+* `sign-ext`
+
+If you're compiling WebAssembly code for an engine that does not support a
+feature in LLVM's default feature set then the feature must be disabled at
+compile time. Note, though, that enabled features may be used in the standard
+library or precompiled libraries shipped via rustup. This means that not only
+does your own code need to be compiled with the correct set of flags but the
+Rust standard library additionally must be recompiled.
+
+Compiling all code for the initial release of WebAssembly looks like:
+
+```sh
+$ export RUSTFLAGS=-Ctarget-cpu=mvp
+$ cargo +nightly build -Zbuild-std=panic_abort,std --target wasm32-unknown-unknown
+```
+
+Here the `mvp` "cpu" is a placeholder in LLVM for disabling all supported
+features by default. Cargo's `-Zbuild-std` feature, a Nightly Rust feature, is
+then used to recompile the standard library in addition to your own code. This
+will produce a binary that uses only the original WebAssembly features by
+default and no proposals since its inception.
+
+To enable individual features it can be done with `-Ctarget-feature=+foo`.
+Available features for Rust code itself are documented in the [reference] and
+can also be found through:
+
+```sh
+$ rustc -Ctarget-feature=help --target wasm32-unknown-unknown
+```
+
+You'll need to consult your WebAssembly engine's documentation to learn more
+about the supported WebAssembly features the engine has.
+
+[reference]: https://doc.rust-lang.org/reference/attributes/codegen.html#wasm32-or-wasm64
+
+Note that it is still possible for Rust crates and libraries to enable
+WebAssembly features on a per-function level. This means that the build
+command above may not be sufficient to disable all WebAssembly features. If the
+final binary still has SIMD instructions, for example, the function in question
+will need to be found and the crate in question will likely contain something
+like:
+
+```rust,ignore (not-always-compiled-to-wasm)
+#[target_feature(enable = "simd128")]
+fn foo() {
+    // ...
+}
+```
+
+In this situation there is no compiler flag to disable emission of SIMD
+instructions and the crate must instead be modified to not include this function
+at compile time either by default or through a Cargo feature. For crate authors
+it's recommended to avoid `#[target_feature(enable = "...")]` except where
+necessary and instead use:
+
+```rust,ignore (not-always-compiled-to-wasm)
+#[cfg(target_feature = "simd128")]
+fn foo() {
+    // ...
+}
+```
+
+That is to say instead of enabling target features it's recommended to
+conditionally compile code instead. This is notably different to the way native
+platforms such as x86\_64 work, and this is due to the fact that WebAssembly
+binaries must only contain code the engine understands. Native binaries work so
+long as the CPU doesn't execute unknown code dynamically at runtime.

src/doc/rustc/src/platform-support/wasm32-wasip1-threads.md

@@ -162,3 +162,17 @@ It's recommended to conditionally compile code for this target with:
 Prior to Rust 1.80 the `target_env = "p1"` key was not set. Currently the
 `target_feature = "atomics"` is Nightly-only. Note that the precise `#[cfg]`
 necessary to detect this target may change as the target becomes more stable.
+
+## Enabled WebAssembly features
+
+The default set of WebAssembly features enabled for compilation includes two
+more features in addition to that which
+[`wasm32-unknown-unknown`](./wasm32-unknown-unknown.md) enables:
+
+* `bulk-memory`
+* `atomics`
+
+For more information about features see the documentation for
+[`wasm32-unknown-unknown`](./wasm32-unknown-unknown.md), but note that the
+`mvp` CPU in LLVM does not support this target as it's required that
+`bulk-memory`, `atomics`, and `mutable-globals` are all enabled.

src/doc/rustc/src/platform-support/wasm32-wasip1.md

@@ -132,3 +132,9 @@ It's recommended to conditionally compile code for this target with:
 
 Note that the `target_env = "p1"` condition first appeared in Rust 1.80. Prior
 to Rust 1.80 the `target_env` condition was not set.
+
+## Enabled WebAssembly features
+
+The default set of WebAssembly features enabled for compilation is currently the
+same as [`wasm32-unknown-unknown`](./wasm32-unknown-unknown.md). See the
+documentation there for more information.

src/doc/rustc/src/platform-support/wasm32-wasip2.md

@@ -61,3 +61,9 @@ It's recommended to conditionally compile code for this target with:
 ```text
 #[cfg(all(target_os = "wasi", target_env = "p2"))]
 ```
+
+## Enabled WebAssembly features
+
+The default set of WebAssembly features enabled for compilation is currently the
+same as [`wasm32-unknown-unknown`](./wasm32-unknown-unknown.md). See the
+documentation there for more information.