Auto merge of rust-lang#76186 - tmandry:rollup-49nliiy, r=tmandry

Rollup of 12 pull requests

Successful merges:

 - rust-lang#75945 (Use `env::func()`, not 'the function env::func' in docs for std::env)
 - rust-lang#76002 (Fix `-Z instrument-coverage` on MSVC)
 - rust-lang#76003 (Adds two source span utility functions used in source-based coverage)
 - rust-lang#76059 (Clean up E0764)
 - rust-lang#76103 (Clean up E0769)
 - rust-lang#76139 (Make `cow_is_borrowed` methods const)
 - rust-lang#76154 (Fix rustdoc strings indentation)
 - rust-lang#76161 (Remove notrust in rustc_middle)
 - rust-lang#76163 (README: Adjust Linux and macOS support platform and architecture)
 - rust-lang#76166 (Make `StringReader` private)
 - rust-lang#76172 (Revert rust-lang#75463)
 - rust-lang#76178 (Update expect-test to 1.0)

Failed merges:

r? @ghost

Cargo.lock

@@ -998,9 +998,9 @@ dependencies = [
 
 [[package]]
 name = "expect-test"
-version = "0.1.0"
+version = "1.0.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a3e383741ea1982866572109d1a8c807bd36aad91fca701489fdca56ef92b3b8"
+checksum = "ceb96f3eaa0d4e8769c52dacfd4eb60183b817ed2f176171b3c691d5022b0f2e"
 dependencies = [
  "difference",
  "once_cell",

README.md

@@ -211,11 +211,17 @@ fetch snapshots, and an OS that can execute the available snapshot binaries.
 
 Snapshot binaries are currently built and tested on several platforms:
 
-| Platform / Architecture    | x86 | x86_64 |
-|----------------------------|-----|--------|
-| Windows (7, 8, 10, ...)    | ✓   | ✓      |
-| Linux (2.6.18 or later)    | ✓   | ✓      |
-| macOS (10.7 Lion or later) | ✓   | ✓      |
+| Platform / Architecture                     | x86 | x86_64 |
+|---------------------------------------------|-----|--------|
+| Windows (7, 8, 10, ...)                     | ✓   | ✓      |
+| Linux (kernel 2.6.32, glibc 2.11 or later)  | ✓   | ✓      |
+| macOS (10.7 Lion or later)                  | (\*) | ✓      |
+
+(\*): Apple dropped support for running 32-bit binaries starting from macOS 10.15 and iOS 11.
+Due to this decision from Apple, the targets are no longer useful to our users.
+Please read [our blog post][macx32] for more info.
+
+[macx32]: https://blog.rust-lang.org/2020/01/03/reducing-support-for-32-bit-apple-targets.html
 
 You may find that other platforms work, but these are our officially
 supported build environments that are most likely to work.

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -1668,7 +1668,7 @@ fn linker_with_args<'a, B: ArchiveBuilder<'a>>(
     // FIXME: Order dependent, applies to the following objects. Where should it be placed?
     // Try to strip as much out of the generated object by removing unused
     // sections if possible. See more comments in linker.rs
-    if sess.opts.cg.link_dead_code != Some(true) {
+    if !sess.link_dead_code() {
         let keep_metadata = crate_type == CrateType::Dylib;
         cmd.gc_sections(keep_metadata);
     }

compiler/rustc_error_codes/src/error_codes/E0764.md

@@ -1,12 +1,4 @@
-Mutable references (`&mut`) can only be used in constant functions, not statics
-or constants. This limitation exists to prevent the creation of constants that
-have a mutable reference in their final value. If you had a constant of `&mut
-i32` type, you could modify the value through that reference, making the
-constant essentially mutable. While there could be a more fine-grained scheme
-in the future that allows mutable references if they are not "leaked" to the
-final value, a more conservative approach was chosen for now. `const fn` do not
-have this problem, as the borrow checker will prevent the `const fn` from
-returning new mutable references.
+A mutable reference was used in a constant.
 
 Erroneous code example:
 
@@ -19,6 +11,18 @@ fn main() {
 }
 ```
 
+Mutable references (`&mut`) can only be used in constant functions, not statics
+or constants. This limitation exists to prevent the creation of constants that
+have a mutable reference in their final value. If you had a constant of
+`&mut i32` type, you could modify the value through that reference, making the
+constant essentially mutable.
+
+While there could be a more fine-grained scheme in the future that allows
+mutable references if they are not "leaked" to the final value, a more
+conservative approach was chosen for now. `const fn` do not have this problem,
+as the borrow checker will prevent the `const fn` from returning new mutable
+references.
+
 Remember: you cannot use a function call inside a constant or static. However,
 you can totally use it in constant functions:
 

compiler/rustc_error_codes/src/error_codes/E0769.md

@@ -1,15 +1,19 @@
-A tuple struct or tuple variant was used in a pattern as if it were a
-struct or struct variant.
+A tuple struct or tuple variant was used in a pattern as if it were a struct or
+struct variant.
 
 Erroneous code example:
 
 ```compile_fail,E0769
 enum E {
     A(i32),
 }
+
 let e = E::A(42);
+
 match e {
-    E::A { number } => println!("{}", x),
+    E::A { number } => { // error!
+        println!("{}", number);
+    }
 }
 ```
 
@@ -21,19 +25,23 @@ To fix this error, you can use the tuple pattern:
 # }
 # let e = E::A(42);
 match e {
-    E::A(number) => println!("{}", number),
+    E::A(number) => { // ok!
+        println!("{}", number);
+    }
 }
 ```
 
-Alternatively, you can also use the struct pattern by using the correct
-field names and binding them to new identifiers:
+Alternatively, you can also use the struct pattern by using the correct field
+names and binding them to new identifiers:
 
 ```
 # enum E {
 #     A(i32),
 # }
 # let e = E::A(42);
 match e {
-    E::A { 0: number } => println!("{}", number),
+    E::A { 0: number } => { // ok!
+        println!("{}", number);
+    }
 }
 ```

compiler/rustc_lexer/Cargo.toml

@@ -20,4 +20,4 @@ doctest = false
 unicode-xid = "0.2.0"
 
 [dev-dependencies]
-expect-test = "0.1"
+expect-test = "1.0"

compiler/rustc_middle/src/mir/mono.rs

@@ -85,7 +85,7 @@ impl<'tcx> MonoItem<'tcx> {
             .debugging_opts
             .inline_in_all_cgus
             .unwrap_or_else(|| tcx.sess.opts.optimize != OptLevel::No)
-            && tcx.sess.opts.cg.link_dead_code != Some(true);
+            && !tcx.sess.link_dead_code();
 
         match *self {
             MonoItem::Fn(ref instance) => {

compiler/rustc_middle/src/ty/walk.rs

@@ -55,7 +55,7 @@ impl GenericArg<'tcx> {
     /// that appear in `self`, it does not descend into the fields of
     /// structs or variants. For example:
     ///
-    /// ```notrust
+    /// ```text
     /// isize => { isize }
     /// Foo<Bar<isize>> => { Foo<Bar<isize>>, Bar<isize>, isize }
     /// [isize] => { [isize], isize }
@@ -80,7 +80,7 @@ impl<'tcx> super::TyS<'tcx> {
     /// that appear in `self`, it does not descend into the fields of
     /// structs or variants. For example:
     ///
-    /// ```notrust
+    /// ```text
     /// isize => { isize }
     /// Foo<Bar<isize>> => { Foo<Bar<isize>>, Bar<isize>, isize }
     /// [isize] => { [isize], isize }

compiler/rustc_mir/src/monomorphize/partitioning/mod.rs

@@ -190,7 +190,7 @@ pub fn partition<'tcx>(
 
     // Next we try to make as many symbols "internal" as possible, so LLVM has
     // more freedom to optimize.
-    if tcx.sess.opts.cg.link_dead_code != Some(true) {
+    if !tcx.sess.link_dead_code() {
         let _prof_timer = tcx.prof.generic_activity("cgu_partitioning_internalize_symbols");
         partitioner.internalize_symbols(tcx, &mut post_inlining, inlining_map);
     }
@@ -327,7 +327,7 @@ fn collect_and_partition_mono_items<'tcx>(
             }
         }
         None => {
-            if tcx.sess.opts.cg.link_dead_code == Some(true) {
+            if tcx.sess.link_dead_code() {
                 MonoItemCollectionMode::Eager
             } else {
                 MonoItemCollectionMode::Lazy

compiler/rustc_parse/src/lexer/mod.rs

@@ -27,7 +27,7 @@ pub struct UnmatchedBrace {
     pub candidate_span: Option<Span>,
 }
 
-pub struct StringReader<'a> {
+crate struct StringReader<'a> {
     sess: &'a ParseSess,
     /// Initial position, read-only.
     start_pos: BytePos,
@@ -41,7 +41,7 @@ pub struct StringReader<'a> {
 }
 
 impl<'a> StringReader<'a> {
-    pub fn new(
+    crate fn new(
         sess: &'a ParseSess,
         source_file: Lrc<rustc_span::SourceFile>,
         override_span: Option<Span>,
@@ -66,7 +66,7 @@ impl<'a> StringReader<'a> {
     }
 
     /// Returns the next token, including trivia like whitespace or comments.
-    pub fn next_token(&mut self) -> Token {
+    fn next_token(&mut self) -> Token {
         let start_src_index = self.src_index(self.pos);
         let text: &str = &self.src[start_src_index..self.end_src_index];
 

compiler/rustc_session/src/config.rs

@@ -1718,20 +1718,11 @@ pub fn build_session_options(matches: &getopts::Matches) -> Options {
             );
         }
 
-        // `-Z instrument-coverage` implies:
-        //   * `-Z symbol-mangling-version=v0` - to ensure consistent and reversible name mangling.
-        //     Note, LLVM coverage tools can analyze coverage over multiple runs, including some
-        //     changes to source code; so mangled names must be consistent across compilations.
-        //   * `-C link-dead-code` - so unexecuted code is still counted as zero, rather than be
-        //     optimized out. Note that instrumenting dead code can be explicitly disabled with:
-        //         `-Z instrument-coverage -C link-dead-code=no`.
+        // `-Z instrument-coverage` implies `-Z symbol-mangling-version=v0` - to ensure consistent
+        // and reversible name mangling. Note, LLVM coverage tools can analyze coverage over
+        // multiple runs, including some changes to source code; so mangled names must be consistent
+        // across compilations.
         debugging_opts.symbol_mangling_version = SymbolManglingVersion::V0;
-        if cg.link_dead_code == None {
-            // FIXME(richkadel): Investigate if the `instrument-coverage` implementation can
-            // inject ["zero counters"](https://llvm.org/docs/CoverageMappingFormat.html#counter)
-            // in the coverage map when "dead code" is removed, rather than forcing `link-dead-code`.
-            cg.link_dead_code = Some(true);
-        }
     }
 
     if !cg.embed_bitcode {

compiler/rustc_session/src/options.rs

@@ -885,9 +885,9 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
         "instrument the generated code to support LLVM source-based code coverage \
         reports (note, the compiler build config must include `profiler = true`, \
         and is mutually exclusive with `-C profile-generate`/`-C profile-use`); \
-        implies `-C link-dead-code` (unless explicitly disabled)` and \
-        `-Z symbol-mangling-version=v0`; and disables/overrides some optimization \
-        options (default: no)"),
+        implies `-C link-dead-code` (unless targeting MSVC, or explicitly disabled) \
+        and `-Z symbol-mangling-version=v0`; disables/overrides some Rust \
+        optimizations (default: no)"),
     instrument_mcount: bool = (false, parse_bool, [TRACKED],
         "insert function instrument code for mcount-based tracing (default: no)"),
     keep_hygiene_data: bool = (false, parse_bool, [UNTRACKED],

compiler/rustc_session/src/session.rs

@@ -1024,6 +1024,40 @@ impl Session {
         || self.opts.debugging_opts.sanitizer.intersects(SanitizerSet::ADDRESS | SanitizerSet::MEMORY)
     }
 
+    pub fn link_dead_code(&self) -> bool {
+        match self.opts.cg.link_dead_code {
+            Some(explicitly_set) => explicitly_set,
+            None => {
+                self.opts.debugging_opts.instrument_coverage
+                    && !self.target.target.options.is_like_msvc
+                // Issue #76038: (rustc `-Clink-dead-code` causes MSVC linker to produce invalid
+                // binaries when LLVM InstrProf counters are enabled). As described by this issue,
+                // the "link dead code" option produces incorrect binaries when compiled and linked
+                // under MSVC. The resulting Rust programs typically crash with a segmentation
+                // fault, or produce an empty "*.profraw" file (profiling counter results normally
+                // generated during program exit).
+                //
+                // If not targeting MSVC, `-Z instrument-coverage` implies `-C link-dead-code`, so
+                // unexecuted code is still counted as zero, rather than be optimized out. Note that
+                // instrumenting dead code can be explicitly disabled with:
+                //
+                //     `-Z instrument-coverage -C link-dead-code=no`.
+                //
+                // FIXME(richkadel): Investigate if `instrument-coverage` implementation can inject
+                // [zero counters](https://llvm.org/docs/CoverageMappingFormat.html#counter) in the
+                // coverage map when "dead code" is removed, rather than forcing `link-dead-code`.
+                // This may not be possible, however, if (as it seems to appear) the "dead code"
+                // that would otherwise not be linked is only identified as "dead" by the native
+                // linker. If that's the case, I believe it is too late for the Rust compiler to
+                // leverage any information it might be able to get from the linker regarding what
+                // code is dead, to be able to add those counters.
+                //
+                // On the other hand, if any Rust compiler passes are optimizing out dead code blocks
+                // we should inject "zero" counters for those code regions.
+            }
+        }
+    }
+
     pub fn mark_attr_known(&self, attr: &Attribute) {
         self.known_attrs.lock().mark(attr)
     }
@@ -1432,20 +1466,6 @@ fn validate_commandline_args_with_session_available(sess: &Session) {
         );
     }
 
-    // FIXME(richkadel): See `src/test/run-make-fulldeps/instrument-coverage/Makefile`. After
-    // compiling with `-Zinstrument-coverage`, the resulting binary generates a segfault during
-    // the program's exit process (likely while attempting to generate the coverage stats in
-    // the "*.profraw" file). An investigation to resolve the problem on Windows is ongoing,
-    // but until this is resolved, the option is disabled on Windows, and the test is skipped
-    // when targeting `MSVC`.
-    if sess.opts.debugging_opts.instrument_coverage && sess.target.target.options.is_like_msvc {
-        sess.warn(
-            "Rust source-based code coverage instrumentation (with `-Z instrument-coverage`) \
-            is not yet supported on Windows when targeting MSVC. The resulting binaries will \
-            still be instrumented for experimentation purposes, but may not execute correctly.",
-        );
-    }
-
     const ASAN_SUPPORTED_TARGETS: &[&str] = &[
         "aarch64-fuchsia",
         "aarch64-unknown-linux-gnu",

compiler/rustc_span/src/lib.rs

@@ -400,6 +400,13 @@ impl Span {
         span.with_lo(span.hi)
     }
 
+    #[inline]
+    /// Returns true if hi == lo
+    pub fn is_empty(&self) -> bool {
+        let span = self.data();
+        span.hi == span.lo
+    }
+
     /// Returns `self` if `self` is not the dummy span, and `other` otherwise.
     pub fn substitute_dummy(self, other: Span) -> Span {
         if self.is_dummy() { other } else { self }

compiler/rustc_span/src/source_map.rs

@@ -487,6 +487,15 @@ impl SourceMap {
         }
     }
 
+    /// Returns a new `Span` covering the start and end `BytePos`s of the file containing the given
+    /// `pos`. This can be used to quickly determine if another `BytePos` or `Span` is from the same
+    /// file.
+    pub fn lookup_file_span(&self, pos: BytePos) -> Span {
+        let idx = self.lookup_source_file_idx(pos);
+        let SourceFile { start_pos, end_pos, .. } = *(*self.files.borrow().source_files)[idx];
+        Span::with_root_ctxt(start_pos, end_pos)
+    }
+
     /// Returns `Some(span)`, a union of the LHS and RHS span. The LHS must precede the RHS. If
     /// there are gaps between LHS and RHS, the resulting union will cross these gaps.
     /// For this to work,

library/alloc/src/borrow.rs

@@ -217,7 +217,7 @@ impl<B: ?Sized + ToOwned> Cow<'_, B> {
     /// assert!(!bull.is_borrowed());
     /// ```
     #[unstable(feature = "cow_is_borrowed", issue = "65143")]
-    pub fn is_borrowed(&self) -> bool {
+    pub const fn is_borrowed(&self) -> bool {
         match *self {
             Borrowed(_) => true,
             Owned(_) => false,
@@ -239,7 +239,7 @@ impl<B: ?Sized + ToOwned> Cow<'_, B> {
     /// assert!(!bull.is_owned());
     /// ```
     #[unstable(feature = "cow_is_borrowed", issue = "65143")]
-    pub fn is_owned(&self) -> bool {
+    pub const fn is_owned(&self) -> bool {
         !self.is_borrowed()
     }
 

library/core/src/cmp.rs

@@ -356,9 +356,8 @@ impl Ordering {
     /// ```
     #[inline]
     #[must_use]
-    #[rustc_const_stable(feature = "const_ordering", since = "1.48.0")]
     #[stable(feature = "rust1", since = "1.0.0")]
-    pub const fn reverse(self) -> Ordering {
+    pub fn reverse(self) -> Ordering {
         match self {
             Less => Greater,
             Equal => Equal,
@@ -395,9 +394,8 @@ impl Ordering {
     /// ```
     #[inline]
     #[must_use]
-    #[rustc_const_stable(feature = "const_ordering", since = "1.48.0")]
     #[stable(feature = "ordering_chaining", since = "1.17.0")]
-    pub const fn then(self, other: Ordering) -> Ordering {
+    pub fn then(self, other: Ordering) -> Ordering {
         match self {
             Equal => other,
             _ => self,