[testutil] Initial commit

The `testutil` crate currently supports extracting pinned toolchain
versions and comparing these to the toolchain version used to run the
test. This is used to replace `#[rustversion::*]` attributes. While it
adds more code, it also means that, in order to roll pinned toolchain
versions, only the root `Cargo.toml` needs to be updated (previously, it
was also necessary to update `tests/trybuild.rs` and
`zerocopy-derive/tests/trybuild.rs`). This paves the way to automate the
rolling of pinned toolchain versions (see #348).

Cargo.toml

@@ -60,6 +60,7 @@ itertools = "0.11"
 rand = { version = "0.8.5", features = ["small_rng"] }
 rustversion = "1.0"
 static_assertions = "1.1"
+testutil = { path = "testutil" }
 # Pinned to a specific version so that the version used for local development
 # and the version used in CI are guaranteed to be the same. Future versions
 # sometimes change the output format slightly, so a version mismatch can cause

tests/trybuild.rs

@@ -2,31 +2,18 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// UI tests depend on the exact error messages emitted by rustc, but those error
-// messages are not stable, and sometimes change between Rust versions. Thus, we
-// maintain one set of UI tests for each Rust version that we test in CI, and we
-// pin to specific versions in CI (a specific stable version, a specific date of
-// the nightly compiler, and a specific MSRV). Updating those pinned versions
-// may also require updating these tests.
-// - `tests/ui-nightly` - Contains the source of truth for our UI test source
-//   files (`.rs`), and contains `.err` and `.out` files for nightly
-// - `tests/ui-stable` - Contains symlinks to the `.rs` files in
-//   `tests/ui-nightly`, and contains `.err` and `.out` files for stable
-// - `tests/ui-msrv` - Contains symlinks to the `.rs` files in
-//   `tests/ui-nightly`, and contains `.err` and `.out` files for MSRV
-
-#[rustversion::nightly]
-const SOURCE_FILES_DIR: &str = "tests/ui-nightly";
-#[rustversion::stable(1.69.0)]
-const SOURCE_FILES_DIR: &str = "tests/ui-stable";
-#[rustversion::stable(1.61.0)]
-const SOURCE_FILES_DIR: &str = "tests/ui-msrv";
+use testutil::ToolchainVersion;
 
 #[test]
 #[cfg_attr(miri, ignore)]
 fn ui() {
+    let version = ToolchainVersion::extract_from_pwd().unwrap();
+    // See the doc comment on this method for an explanation of what this does
+    // and why we store source files in different directories.
+    let source_files_dirname = version.get_ui_source_files_dirname_and_maybe_print_warning();
+
     let t = trybuild::TestCases::new();
-    t.compile_fail(format!("{SOURCE_FILES_DIR}/*.rs"));
+    t.compile_fail(format!("tests/{source_files_dirname}/*.rs"));
 }
 
 // The file `invalid-impls.rs` directly includes `src/macros.rs` in order to
@@ -40,6 +27,11 @@ fn ui() {
 #[test]
 #[cfg_attr(miri, ignore)]
 fn ui_invalid_impls() {
+    let version = ToolchainVersion::extract_from_pwd().unwrap();
+    // See the doc comment on this method for an explanation of what this does
+    // and why we store source files in different directories.
+    let source_files_dirname = version.get_ui_source_files_dirname_and_maybe_print_warning();
+
     let t = trybuild::TestCases::new();
-    t.compile_fail(format!("{SOURCE_FILES_DIR}/invalid-impls/*.rs"));
+    t.compile_fail(format!("tests/{source_files_dirname}/invalid-impls/*.rs"));
 }

testutil/Cargo.toml

@@ -0,0 +1,15 @@
+# Copyright 2023 The Fuchsia Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+[package]
+name = "testutil"
+version = "0.0.0"
+edition = "2021"
+
+[dependencies]
+cargo_metadata = "0.18.0"
+rustc_version = "0.4.0"
+# Pin to 0.3.0 because more recent versions require a Rust version more recent
+# than our MSRV.
+time = { version = "=0.3.0", default-features = false, features = ["formatting", "macros", "parsing"] }

testutil/src/lib.rs

@@ -0,0 +1,155 @@
+// Copyright 2023 The Fuchsia Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+use cargo_metadata::MetadataCommand;
+use rustc_version::{Channel, Version};
+use std::error::Error;
+
+struct PinnedVersions {
+    msrv: String,
+    stable: String,
+    nightly: String,
+}
+
+impl PinnedVersions {
+    /// Attempts to extract pinned toolchain versions based on the current
+    /// working directory.
+    ///
+    /// `extract_from_pwd` expects to be called from a directory which is a
+    /// child of a Cargo workspace. It extracts the pinned versions from the
+    /// metadata of the root package.
+    fn extract_from_pwd() -> Result<PinnedVersions, Box<dyn Error>> {
+        let meta = MetadataCommand::new().exec()?;
+        // NOTE(joshlf): In theory `meta.root_package()` should work instead of
+        // this manual search, but for some reason it breaks when called from
+        // zerocopy-derive's tests. This works as a workaround, and it's just
+        // test code, so I didn't bother investigating.
+        let pkg = meta
+            .workspace_packages()
+            .into_iter()
+            .find(|pkg| pkg.name == "zerocopy")
+            .ok_or("no `zerocopy` package found; are we in a workspace?")?;
+        let msrv = pkg
+            .rust_version
+            .as_ref()
+            .ok_or("failed to find msrv: no `rust-version` key present")?
+            .to_string();
+        let extract = |version_name, key| -> Result<String, String> {
+            let value = pkg.metadata.pointer(&format!("/ci/{key}")).ok_or_else(|| {
+                format!("failed to find {version_name}: no `metadata.ci.{key}` key present")
+            })?;
+            value.as_str().map(str::to_string).ok_or_else(|| format!("failed to find {version_name}: key `metadata.ci.{key}` (contents: {value:?}) failed to parse as JSON string"))
+        };
+        let stable = extract("stable", "pinned-stable")?;
+        let nightly = extract("nightly", "pinned-nightly")?;
+        Ok(PinnedVersions { msrv, stable, nightly })
+    }
+}
+
+#[derive(Debug)]
+pub enum ToolchainVersion {
+    /// The version listed as our MSRV (ie, the `package.rust-version` key in
+    /// `Cargo.toml`).
+    PinnedMsrv,
+    /// The stable version pinned in CI.
+    PinnedStable,
+    /// The nightly version pinned in CI
+    PinnedNightly,
+    /// A stable version other than the one pinned in CI.
+    OtherStable,
+    /// A nightly version other than the one pinned in CI.
+    OtherNightly,
+}
+
+impl ToolchainVersion {
+    /// Attempts to determine whether the current toolchain version matches one
+    /// of the versions pinned in CI and if so, which one.
+    pub fn extract_from_pwd() -> Result<ToolchainVersion, Box<dyn Error>> {
+        let pinned_versions = PinnedVersions::extract_from_pwd()?;
+        let current = rustc_version::version_meta()?;
+
+        let s = match current.channel {
+            Channel::Dev | Channel::Beta => {
+                return Err(format!("unsupported channel: {:?}", current.channel).into())
+            }
+            Channel::Nightly => {
+                format!(
+                    "nightly-{}",
+                    current.commit_date.as_ref().ok_or("nightly channel missing commit date")?
+                )
+            }
+            Channel::Stable => {
+                let Version { major, minor, patch, .. } = current.semver;
+                format!("{major}.{minor}.{patch}")
+            }
+        };
+
+        // Due to a quirk of how Rust nightly versions are encoded and published
+        // [1], the version as understood by rustup uses a date one day ahead of
+        // the version as encoded in the `rustc` binary itself.
+        // `pinned_versions` encodes the former notion of the date (as it is
+        // meant to be passed as the `+<toolchain>` selector syntax understood
+        // by rustup), while `current` encodes the latter notion of the date (as
+        // it is extracted from `rustc`). Without this adjustment, toolchain
+        // versions that should be considered equal would not be.
+        //
+        // [1] https://github.com/rust-lang/rust/issues/51533
+        let pinned_nightly_adjusted = {
+            let desc = time::macros::format_description!("nightly-[year]-[month]-[day]");
+            let date = time::Date::parse(&pinned_versions.nightly, &desc).map_err(|_| {
+                format!("failed to parse nightly version: {}", pinned_versions.nightly)
+            })?;
+            let adjusted = date - time::Duration::DAY;
+            adjusted.format(&desc).unwrap()
+        };
+
+        Ok(match s {
+            s if s == pinned_versions.msrv => ToolchainVersion::PinnedMsrv,
+            s if s == pinned_versions.stable => ToolchainVersion::PinnedStable,
+            s if s == pinned_nightly_adjusted => ToolchainVersion::PinnedNightly,
+            _ if current.channel == Channel::Stable => ToolchainVersion::OtherStable,
+            _ if current.channel == Channel::Nightly => ToolchainVersion::OtherNightly,
+            _ => {
+                return Err(format!(
+                    "current toolchain ({current:?}) doesn't match any known version"
+                )
+                .into())
+            }
+        })
+    }
+
+    /// Gets the name of the directory in which to store source files and
+    /// expected output for UI tests for this toolchain version.
+    ///
+    /// For toolchain versions which are not pinned in CI, prints a warning to
+    /// `stderr` which will be captured by the test harness and only printed on
+    /// test failure.
+    ///
+    /// UI tests depend on the exact error messages emitted by rustc, but those
+    /// error messages are not stable, and sometimes change between Rust
+    /// versions. Thus, we maintain one set of UI tests for each Rust version
+    /// that we test in CI, and we pin to specific versions in CI (a specific
+    /// MSRV, a specific stable version, and a specific date of the nightly
+    /// compiler). Updating those pinned versions may also require updating
+    /// these tests.
+    /// - `tests/ui-nightly` - Contains the source of truth for our UI test
+    ///   source files (`.rs`), and contains `.err` and `.out` files for nightly
+    /// - `tests/ui-stable` - Contains symlinks to the `.rs` files in
+    ///   `tests/ui-nightly`, and contains `.err` and `.out` files for stable
+    /// - `tests/ui-msrv` - Contains symlinks to the `.rs` files in
+    ///   `tests/ui-nightly`, and contains `.err` and `.out` files for MSRV
+    pub fn get_ui_source_files_dirname_and_maybe_print_warning(&self) -> &'static str {
+        if matches!(self, ToolchainVersion::OtherStable | ToolchainVersion::OtherNightly) {
+            // This will be eaten by the test harness and only displayed on
+            // failure.
+            eprintln!("warning: current toolchain does not match any toolchain pinned in CI; this may cause spurious test failure");
+        }
+
+        match self {
+            ToolchainVersion::PinnedMsrv => "ui-msrv",
+            ToolchainVersion::PinnedStable | ToolchainVersion::OtherStable => "ui-stable",
+            ToolchainVersion::PinnedNightly | ToolchainVersion::OtherNightly => "ui-nightly",
+        }
+    }
+}

zerocopy-derive/Cargo.toml

@@ -23,11 +23,11 @@ quote = "1.0.10"
 syn = "2.0.31"
 
 [dev-dependencies]
-rustversion = "1.0"
 static_assertions = "1.1"
+testutil = { path = "../testutil" }
 # Pinned to a specific version so that the version used for local development
 # and the version used in CI are guaranteed to be the same. Future versions
 # sometimes change the output format slightly, so a version mismatch can cause
 # CI test failures.
 trybuild = "=1.0.80"
-zerocopy = { path = "../", features = ["default", "derive"] }
+zerocopy = { path = "../", features = ["default", "derive"] }

zerocopy-derive/tests/trybuild.rs

@@ -2,29 +2,14 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// UI tests depend on the exact error messages emitted by rustc, but those error
-// messages are not stable, and sometimes change between Rust versions. Thus, we
-// maintain one set of UI tests for each Rust version that we test in CI, and we
-// pin to specific versions in CI (a specific stable version, a specific date of
-// the nightly compiler, and a specific MSRV). Updating those pinned versions
-// may also require updating these tests.
-// - `tests/ui-nightly` - Contains the source of truth for our UI test source
-//   files (`.rs`), and contains `.err` and `.out` files for nightly
-// - `tests/ui-stable` - Contains symlinks to the `.rs` files in
-//   `tests/ui-nightly`, and contains `.err` and `.out` files for stable
-// - `tests/ui-msrv` - Contains symlinks to the `.rs` files in
-//   `tests/ui-nightly`, and contains `.err` and `.out` files for MSRV
-
-#[rustversion::nightly]
-const SOURCE_FILES_GLOB: &str = "tests/ui-nightly/*.rs";
-#[rustversion::stable(1.69.0)]
-const SOURCE_FILES_GLOB: &str = "tests/ui-stable/*.rs";
-#[rustversion::stable(1.61.0)]
-const SOURCE_FILES_GLOB: &str = "tests/ui-msrv/*.rs";
-
 #[test]
 #[cfg_attr(miri, ignore)]
 fn ui() {
+    let version = testutil::ToolchainVersion::extract_from_pwd().unwrap();
+    // See the doc comment on this method for an explanation of what this does
+    // and why we store source files in different directories.
+    let source_files_dirname = version.get_ui_source_files_dirname_and_maybe_print_warning();
+
     let t = trybuild::TestCases::new();
-    t.compile_fail(SOURCE_FILES_GLOB);
+    t.compile_fail(format!("tests/{source_files_dirname}/*.rs"));
 }