Auto merge of rust-lang#100591 - est31:stabilization_placeholder, r=Mark-Simulacrum

Require stabilizations to use a placeholder instead of writing out stabilization version

Implements the idea from [this](https://rust-lang.zulipchat.com/#narrow/stream/241545-t-release/topic/libs.20stabilization.20placeholder) zulip stream.

It's a common phenomenon that feature stabilizations don't make it into a particular release, but the version is still inaccurate. Often this is caught in the PR, but it can also require subsequent changes to adjust/correct the version. A list with examples of such PRs is given in rust-lang#100577, but it's far from complete.

This PR requires stabilization PRs to use the placeholder `CURRENT_RUSTC_VERSION`, enforced via tidy tooling. The PR also adds a tool that replaces the placeholder with the version number. It can be invoked via `./x.py run src/tools/replace-version-placeholder` and is supposed to be ran upon beta branching as well as version bumping and any backports to the beta branch.  I filed PRs to the dev guide and forge to document these changes in the release and stabilization workflows:

* The [dev guide](https://rustc-dev-guide.rust-lang.org/stabilization_guide.html#determining-the-stabilization-version) PR: rust-lang/rustc-dev-guide#1443
* The [std dev guide](https://std-dev-guide.rust-lang.org/) PR: rust-lang/std-dev-guide#43
* The [forge](https://github.com/rust-lang/rust-forge) PR: rust-lang/rust-forge#643

Alternative to rust-lang#100577 which added checking.

Author: bors

Cargo.lock

@@ -3293,6 +3293,14 @@ dependencies = [
  "winapi",
 ]
 
+[[package]]
+name = "replace-version-placeholder"
+version = "0.1.0"
+dependencies = [
+ "tidy",
+ "walkdir",
+]
+
 [[package]]
 name = "rls"
 version = "1.41.0"

Cargo.toml

@@ -35,6 +35,7 @@ members = [
   "src/tools/jsondocck",
   "src/tools/html-checker",
   "src/tools/bump-stage0",
+  "src/tools/replace-version-placeholder",
   "src/tools/lld-wrapper",
 ]
 

compiler/rustc_feature/src/accepted.rs

@@ -187,7 +187,7 @@ declare_features! (
     /// especially around globs and shadowing (RFC 1560).
     (accepted, item_like_imports, "1.15.0", Some(35120), None),
     /// Allows `'a: { break 'a; }`.
-    (accepted, label_break_value, "1.65.0", Some(48594), None),
+    (accepted, label_break_value, "CURRENT_RUSTC_VERSION", Some(48594), None),
     /// Allows `if/while p && let q = r && ...` chains.
     (accepted, let_chains, "1.64.0", Some(53667), None),
     /// Allows `break {expr}` with a value inside `loop`s.

compiler/rustc_passes/src/lib_features.rs

@@ -54,6 +54,14 @@ impl<'tcx> LibFeatureCollector<'tcx> {
                         }
                     }
                 }
+                const VERSION_PLACEHOLDER: &str = "CURRENT_RUSTC_VERSION";
+
+                if let Some(s) = since && s.as_str() == VERSION_PLACEHOLDER {
+                    let version = option_env!("CFG_VERSION").unwrap_or("<current>");
+                    let version = version.split(' ').next().unwrap();
+                    since = Some(Symbol::intern(&version));
+                }
+
                 if let Some(feature) = feature {
                     // This additional check for stability is to make sure we
                     // don't emit additional, irrelevant errors for malformed

library/core/src/ptr/const_ptr.rs

@@ -95,8 +95,8 @@ impl<T: ?Sized> *const T {
     ///
     /// This is a bit safer than `as` because it wouldn't silently change the type if the code is
     /// refactored.
-    #[stable(feature = "ptr_const_cast", since = "1.65.0")]
-    #[rustc_const_stable(feature = "ptr_const_cast", since = "1.65.0")]
+    #[stable(feature = "ptr_const_cast", since = "CURRENT_RUSTC_VERSION")]
+    #[rustc_const_stable(feature = "ptr_const_cast", since = "CURRENT_RUSTC_VERSION")]
     pub const fn cast_mut(self) -> *mut T {
         self as _
     }

library/core/src/ptr/mut_ptr.rs

@@ -100,8 +100,8 @@ impl<T: ?Sized> *mut T {
     /// coercion.
     ///
     /// [`cast_mut`]: #method.cast_mut
-    #[stable(feature = "ptr_const_cast", since = "1.65.0")]
-    #[rustc_const_stable(feature = "ptr_const_cast", since = "1.65.0")]
+    #[stable(feature = "ptr_const_cast", since = "CURRENT_RUSTC_VERSION")]
+    #[rustc_const_stable(feature = "ptr_const_cast", since = "CURRENT_RUSTC_VERSION")]
     pub const fn cast_const(self) -> *const T {
         self as _
     }

library/std/src/backtrace.rs

@@ -58,7 +58,7 @@
 //! `RUST_LIB_BACKTRACE` or `RUST_BACKTRACE` at runtime might not actually change
 //! how backtraces are captured.
 
-#![stable(feature = "backtrace", since = "1.65.0")]
+#![stable(feature = "backtrace", since = "CURRENT_RUSTC_VERSION")]
 
 #[cfg(test)]
 mod tests;
@@ -104,29 +104,29 @@ use crate::vec::Vec;
 /// previous point in time. In some instances the `Backtrace` type may
 /// internally be empty due to configuration. For more information see
 /// `Backtrace::capture`.
-#[stable(feature = "backtrace", since = "1.65.0")]
+#[stable(feature = "backtrace", since = "CURRENT_RUSTC_VERSION")]
 #[must_use]
 pub struct Backtrace {
     inner: Inner,
 }
 
 /// The current status of a backtrace, indicating whether it was captured or
 /// whether it is empty for some other reason.
-#[stable(feature = "backtrace", since = "1.65.0")]
+#[stable(feature = "backtrace", since = "CURRENT_RUSTC_VERSION")]
 #[non_exhaustive]
 #[derive(Debug, PartialEq, Eq)]
 pub enum BacktraceStatus {
     /// Capturing a backtrace is not supported, likely because it's not
     /// implemented for the current platform.
-    #[stable(feature = "backtrace", since = "1.65.0")]
+    #[stable(feature = "backtrace", since = "CURRENT_RUSTC_VERSION")]
     Unsupported,
     /// Capturing a backtrace has been disabled through either the
     /// `RUST_LIB_BACKTRACE` or `RUST_BACKTRACE` environment variables.
-    #[stable(feature = "backtrace", since = "1.65.0")]
+    #[stable(feature = "backtrace", since = "CURRENT_RUSTC_VERSION")]
     Disabled,
     /// A backtrace has been captured and the `Backtrace` should print
     /// reasonable information when rendered.
-    #[stable(feature = "backtrace", since = "1.65.0")]
+    #[stable(feature = "backtrace", since = "CURRENT_RUSTC_VERSION")]
     Captured,
 }
 
@@ -173,7 +173,7 @@ enum BytesOrWide {
     Wide(Vec<u16>),
 }
 
-#[stable(feature = "backtrace", since = "1.65.0")]
+#[stable(feature = "backtrace", since = "CURRENT_RUSTC_VERSION")]
 impl fmt::Debug for Backtrace {
     fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
         let capture = match &self.inner {
@@ -289,7 +289,7 @@ impl Backtrace {
     ///
     /// To forcibly capture a backtrace regardless of environment variables, use
     /// the `Backtrace::force_capture` function.
-    #[stable(feature = "backtrace", since = "1.65.0")]
+    #[stable(feature = "backtrace", since = "CURRENT_RUSTC_VERSION")]
     #[inline(never)] // want to make sure there's a frame here to remove
     pub fn capture() -> Backtrace {
         if !Backtrace::enabled() {
@@ -308,16 +308,16 @@ impl Backtrace {
     /// Note that capturing a backtrace can be an expensive operation on some
     /// platforms, so this should be used with caution in performance-sensitive
     /// parts of code.
-    #[stable(feature = "backtrace", since = "1.65.0")]
+    #[stable(feature = "backtrace", since = "CURRENT_RUSTC_VERSION")]
     #[inline(never)] // want to make sure there's a frame here to remove
     pub fn force_capture() -> Backtrace {
         Backtrace::create(Backtrace::force_capture as usize)
     }
 
     /// Forcibly captures a disabled backtrace, regardless of environment
     /// variable configuration.
-    #[stable(feature = "backtrace", since = "1.65.0")]
-    #[rustc_const_stable(feature = "backtrace", since = "1.65.0")]
+    #[stable(feature = "backtrace", since = "CURRENT_RUSTC_VERSION")]
+    #[rustc_const_stable(feature = "backtrace", since = "CURRENT_RUSTC_VERSION")]
     pub const fn disabled() -> Backtrace {
         Backtrace { inner: Inner::Disabled }
     }
@@ -361,7 +361,7 @@ impl Backtrace {
     /// Returns the status of this backtrace, indicating whether this backtrace
     /// request was unsupported, disabled, or a stack trace was actually
     /// captured.
-    #[stable(feature = "backtrace", since = "1.65.0")]
+    #[stable(feature = "backtrace", since = "CURRENT_RUSTC_VERSION")]
     #[must_use]
     pub fn status(&self) -> BacktraceStatus {
         match self.inner {
@@ -381,7 +381,7 @@ impl<'a> Backtrace {
     }
 }
 
-#[stable(feature = "backtrace", since = "1.65.0")]
+#[stable(feature = "backtrace", since = "CURRENT_RUSTC_VERSION")]
 impl fmt::Display for Backtrace {
     fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
         let capture = match &self.inner {

src/bootstrap/builder.rs

@@ -647,6 +647,7 @@ impl<'a> Builder<'a> {
                 test::CrateRustdocJsonTypes,
                 test::Linkcheck,
                 test::TierCheck,
+                test::ReplacePlaceholderTest,
                 test::Cargotest,
                 test::Cargo,
                 test::Rls,
@@ -746,7 +747,12 @@ impl<'a> Builder<'a> {
                 install::Src,
                 install::Rustc
             ),
-            Kind::Run => describe!(run::ExpandYamlAnchors, run::BuildManifest, run::BumpStage0),
+            Kind::Run => describe!(
+                run::ExpandYamlAnchors,
+                run::BuildManifest,
+                run::BumpStage0,
+                run::ReplaceVersionPlaceholder,
+            ),
             // These commands either don't use paths, or they're special-cased in Build::build()
             Kind::Clean | Kind::Format | Kind::Setup => vec![],
         }

src/bootstrap/run.rs

@@ -103,3 +103,25 @@ impl Step for BumpStage0 {
         builder.run(&mut cmd);
     }
 }
+
+#[derive(Debug, PartialOrd, Ord, Copy, Clone, Hash, PartialEq, Eq)]
+pub struct ReplaceVersionPlaceholder;
+
+impl Step for ReplaceVersionPlaceholder {
+    type Output = ();
+    const ONLY_HOSTS: bool = true;
+
+    fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
+        run.path("src/tools/replace-version-placeholder")
+    }
+
+    fn make_run(run: RunConfig<'_>) {
+        run.builder.ensure(ReplaceVersionPlaceholder);
+    }
+
+    fn run(self, builder: &Builder<'_>) -> Self::Output {
+        let mut cmd = builder.tool_cmd(Tool::ReplaceVersionPlaceholder);
+        cmd.arg(&builder.src);
+        builder.run(&mut cmd);
+    }
+}

src/bootstrap/test.rs

@@ -2527,6 +2527,43 @@ impl Step for TierCheck {
     }
 }
 
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
+pub struct ReplacePlaceholderTest;
+
+impl Step for ReplacePlaceholderTest {
+    type Output = ();
+    const ONLY_HOSTS: bool = true;
+    const DEFAULT: bool = true;
+
+    /// Ensure the version placeholder replacement tool builds
+    fn run(self, builder: &Builder<'_>) {
+        builder.info("build check for version replacement placeholder");
+
+        // Test the version placeholder replacement tool itself.
+        let bootstrap_host = builder.config.build;
+        let compiler = builder.compiler(0, bootstrap_host);
+        let cargo = tool::prepare_tool_cargo(
+            builder,
+            compiler,
+            Mode::ToolBootstrap,
+            bootstrap_host,
+            "test",
+            "src/tools/replace-version-placeholder",
+            SourceType::InTree,
+            &[],
+        );
+        try_run(builder, &mut cargo.into());
+    }
+
+    fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
+        run.path("src/tools/replace-version-placeholder")
+    }
+
+    fn make_run(run: RunConfig<'_>) {
+        run.builder.ensure(Self);
+    }
+}
+
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub struct LintDocs {
     pub compiler: Compiler,

src/bootstrap/tool.rs

@@ -378,6 +378,7 @@ bootstrap_tool!(
     JsonDocCk, "src/tools/jsondocck", "jsondocck";
     HtmlChecker, "src/tools/html-checker", "html-checker";
     BumpStage0, "src/tools/bump-stage0", "bump-stage0";
+    ReplaceVersionPlaceholder, "src/tools/replace-version-placeholder", "replace-version-placeholder";
 );
 
 #[derive(Debug, Copy, Clone, Hash, PartialEq, Eq, Ord, PartialOrd)]

src/tools/replace-version-placeholder/Cargo.toml

@@ -0,0 +1,10 @@
+[package]
+name = "replace-version-placeholder"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+tidy = { path = "../tidy" }
+walkdir = "2"

src/tools/replace-version-placeholder/src/main.rs

@@ -0,0 +1,30 @@
+use std::path::PathBuf;
+use tidy::{t, walk};
+
+pub const VERSION_PLACEHOLDER: &str = "CURRENT_RUSTC_VERSION";
+
+fn main() {
+    let root_path: PathBuf = std::env::args_os().nth(1).expect("need path to root of repo").into();
+    let version_path = root_path.join("src").join("version");
+    let version_str = t!(std::fs::read_to_string(&version_path), version_path);
+    let version_str = version_str.trim();
+    walk::walk(
+        &root_path,
+        &mut |path| {
+            walk::filter_dirs(path)
+                // We exempt these as they require the placeholder
+                // for their operation
+                || path.ends_with("compiler/rustc_passes/src/lib_features.rs")
+                || path.ends_with("src/tools/tidy/src/features/version.rs")
+                || path.ends_with("src/tools/replace-version-placeholder")
+        },
+        &mut |entry, contents| {
+            if !contents.contains(VERSION_PLACEHOLDER) {
+                return;
+            }
+            let new_contents = contents.replace(VERSION_PLACEHOLDER, version_str);
+            let path = entry.path();
+            t!(std::fs::write(&path, new_contents), path);
+        },
+    );
+}

src/tools/tidy/src/features.rs

@@ -175,6 +175,36 @@ pub fn check(
         tidy_error!(bad, "Found {} features without a gate test.", gate_untested.len());
     }
 
+    let (version, channel) = get_version_and_channel(src_path);
+
+    let all_features_iter = features
+        .iter()
+        .map(|feat| (feat, "lang"))
+        .chain(lib_features.iter().map(|feat| (feat, "lib")));
+    for ((feature_name, feature), kind) in all_features_iter {
+        let since = if let Some(since) = feature.since { since } else { continue };
+        if since > version && since != Version::CurrentPlaceholder {
+            tidy_error!(
+                bad,
+                "The stabilization version {since} of {kind} feature `{feature_name}` is newer than the current {version}"
+            );
+        }
+        if channel == "nightly" && since == version {
+            tidy_error!(
+                bad,
+                "The stabilization version {since} of {kind} feature `{feature_name}` is written out but should be {}",
+                version::VERSION_PLACEHOLDER
+            );
+        }
+        if channel != "nightly" && since == Version::CurrentPlaceholder {
+            tidy_error!(
+                bad,
+                "The placeholder use of {kind} feature `{feature_name}` is not allowed on the {} channel",
+                version::VERSION_PLACEHOLDER
+            );
+        }
+    }
+
     if *bad {
         return CollectedFeatures { lib: lib_features, lang: features };
     }
@@ -195,6 +225,14 @@ pub fn check(
     CollectedFeatures { lib: lib_features, lang: features }
 }
 
+fn get_version_and_channel(src_path: &Path) -> (Version, String) {
+    let version_str = t!(std::fs::read_to_string(src_path.join("version")));
+    let version_str = version_str.trim();
+    let version = t!(std::str::FromStr::from_str(&version_str).map_err(|e| format!("{e:?}")));
+    let channel_str = t!(std::fs::read_to_string(src_path.join("ci").join("channel")));
+    (version, channel_str.trim().to_owned())
+}
+
 fn format_features<'a>(
     features: &'a Features,
     family: &'a str,