[nextest-runner] tidy up libdir support

Make a few changes:

- Remove the ToSummary/FromSummary traits.
- Add PlatformLibdir/PlatformLibdirSummary that represent both available and unavailable platforms
- No need for io::BufRead since the entire output is buffered into a string
- Reorganize code such that the most important types are first in each file.

cargo-nextest/src/dispatch.rs

@@ -27,7 +27,7 @@ use nextest_runner::{
         TestList,
     },
     partition::PartitionerBuilder,
-    platform::{BuildPlatforms, BuildPlatformsTarget},
+    platform::{BuildPlatforms, HostPlatform, PlatformLibdir, TargetPlatform},
     redact::Redactor,
     reporter::{structured, FinalStatusLevel, StatusLevel, TestOutputDisplay, TestReporterBuilder},
     reuse_build::{archive_to_file, ArchiveReporter, PathMapper, ReuseBuildInfo},
@@ -1009,20 +1009,20 @@ impl BaseApp {
         let build_platforms = match reuse_build.binaries_metadata() {
             Some(kind) => kind.binary_list.rust_build_meta.build_platforms.clone(),
             None => {
-                let mut build_platforms = BuildPlatforms::new()?;
-                if let Some(output) = RustcCli::print_host_libdir().read() {
-                    build_platforms.set_host_libdir_from_rustc_output(Cursor::new(output));
-                }
-                if let Some(triple) =
+                let host = HostPlatform::current(PlatformLibdir::from_rustc_stdout(
+                    RustcCli::print_host_libdir().read(),
+                ))?;
+                let target = if let Some(triple) =
                     discover_target_triple(&cargo_configs, cargo_opts.target.as_deref())
                 {
-                    let mut target = BuildPlatformsTarget::new(triple.clone());
-                    if let Some(output) = RustcCli::print_target_libdir(&triple).read() {
-                        target.set_libdir_from_rustc_output(Cursor::new(output));
-                    }
-                    build_platforms.target = Some(target);
-                }
-                build_platforms
+                    let libdir = PlatformLibdir::from_rustc_stdout(
+                        RustcCli::print_target_libdir(&triple).read(),
+                    );
+                    Some(TargetPlatform::new(triple, libdir))
+                } else {
+                    None
+                };
+                BuildPlatforms { host, target }
             }
         };
 

nextest-metadata/src/test_list.rs

@@ -516,6 +516,19 @@ pub struct RustNonTestBinarySummary {
     pub path: Utf8PathBuf,
 }
 
+/// Serialized representation of the host and the target platform.
+#[derive(Clone, Debug, PartialEq, Eq, Deserialize, Serialize)]
+#[serde(rename_all = "kebab-case")]
+pub struct BuildPlatformsSummary {
+    /// The host platform used while compiling the Rust artifacts.
+    pub host: HostPlatformSummary,
+
+    /// The target platforms used while compiling the Rust artifacts.
+    ///
+    /// With current versions of nextest, this will contain at most one element.
+    pub targets: Vec<TargetPlatformSummary>,
+}
+
 /// Serialized representation of the host platform.
 #[derive(Clone, Debug, PartialEq, Eq, Deserialize, Serialize)]
 #[serde(rename_all = "kebab-case")]
@@ -524,10 +537,7 @@ pub struct HostPlatformSummary {
     pub platform: PlatformSummary,
 
     /// The libdir for the host platform.
-    ///
-    /// Empty if failed to discover.
-    #[serde(default)]
-    pub libdir: Option<Utf8PathBuf>,
+    pub libdir: PlatformLibdirSummary,
 }
 
 /// Serialized representation of the target platform.
@@ -539,22 +549,61 @@ pub struct TargetPlatformSummary {
 
     /// The libdir for the target platform.
     ///
-    /// Empty if failed to discover.
-    #[serde(default)]
-    pub libdir: Option<Utf8PathBuf>,
+    /// Err if we failed to discover it.
+    pub libdir: PlatformLibdirSummary,
 }
 
-/// Serialized representation of the host and the target platform.
+/// Serialized representation of a platform's library directory.
 #[derive(Clone, Debug, PartialEq, Eq, Deserialize, Serialize)]
-#[serde(rename_all = "kebab-case")]
-pub struct BuildPlatformsSummary {
-    /// The host platform used while compiling the Rust artifacts.
-    pub host: HostPlatformSummary,
+#[serde(tag = "status", rename_all = "kebab-case")]
+pub enum PlatformLibdirSummary {
+    /// The libdir is available.
+    Available {
+        /// The libdir.
+        path: Utf8PathBuf,
+    },
 
-    /// The target platforms used while compiling the Rust artifacts.
-    ///
-    /// With current versions of nextest, this will contain at most one element.
-    pub targets: Vec<TargetPlatformSummary>,
+    /// The libdir is unavailable, for the reason provided in the inner value.
+    Unavailable {
+        /// The reason why the libdir is unavailable.
+        reason: PlatformLibdirUnavailable,
+    },
+}
+
+/// The reason why a platform libdir is unavailable.
+///
+/// Part of [`PlatformLibdirSummary`].
+///
+/// This is an open-ended enum that may have additional deserializable variants in the future.
+#[derive(Clone, Debug, Eq, PartialEq, Deserialize, Serialize)]
+pub struct PlatformLibdirUnavailable(pub Cow<'static, str>);
+
+impl PlatformLibdirUnavailable {
+    /// The libdir is not available because the rustc invocation to obtain it failed.
+    pub const RUSTC_FAILED: Self = Self::new_const("rustc-failed");
+
+    /// The libdir is not available because it was attempted to be read from rustc, but there was an
+    /// issue with its output.
+    pub const RUSTC_OUTPUT_ERROR: Self = Self::new_const("rustc-output-error");
+
+    /// The libdir is unavailable because it was deserialized from a summary serialized by an older
+    /// version of nextest.
+    pub const OLD_SUMMARY: Self = Self::new_const("old-summary");
+
+    /// Converts a static string into Self.
+    pub const fn new_const(reason: &'static str) -> Self {
+        Self(Cow::Borrowed(reason))
+    }
+
+    /// Converts a string into Self.
+    pub fn new(reason: impl Into<Cow<'static, str>>) -> Self {
+        Self(reason.into())
+    }
+
+    /// Returns self as a string.
+    pub fn as_str(&self) -> &str {
+        &self.0
+    }
 }
 
 /// Information about the kind of a Rust non-test binary.

nextest-runner/src/cargo_config/test_helpers.rs

@@ -1,13 +1,12 @@
 // Copyright (c) The nextest Contributors
 // SPDX-License-Identifier: MIT OR Apache-2.0
 
+use super::TargetTriple;
 use camino::Utf8PathBuf;
 use camino_tempfile::Utf8TempDir;
 use color_eyre::eyre::{Context, Result};
 use target_spec::{Platform, TargetFeatures};
 
-use super::TargetTriple;
-
 pub(super) fn setup_temp_dir() -> Result<Utf8TempDir> {
     let dir = camino_tempfile::Builder::new()
         .tempdir()

nextest-runner/src/config/overrides.rs

@@ -477,8 +477,8 @@ impl CompiledOverride<PreBuildPlatform> {
         self,
         build_platforms: &BuildPlatforms,
     ) -> CompiledOverride<FinalConfig> {
-        let host_eval = self.data.host_spec.eval(&build_platforms.host);
-        let host_test_eval = self.data.target_spec.eval(&build_platforms.host);
+        let host_eval = self.data.host_spec.eval(&build_platforms.host.platform);
+        let host_test_eval = self.data.target_spec.eval(&build_platforms.host.platform);
         let target_eval = build_platforms
             .target
             .as_ref()

nextest-runner/src/config/scripts.rs

@@ -383,8 +383,8 @@ impl CompiledProfileScripts<PreBuildPlatform> {
         self,
         build_platforms: &BuildPlatforms,
     ) -> CompiledProfileScripts<FinalConfig> {
-        let host_eval = self.data.host_spec.eval(&build_platforms.host);
-        let host_test_eval = self.data.target_spec.eval(&build_platforms.host);
+        let host_eval = self.data.host_spec.eval(&build_platforms.host.platform);
+        let host_test_eval = self.data.target_spec.eval(&build_platforms.host.platform);
         let target_eval = build_platforms
             .target
             .as_ref()

nextest-runner/src/config/test_helpers.rs

@@ -4,7 +4,7 @@
 use crate::{
     cargo_config::{TargetDefinitionLocation, TargetTriple, TargetTripleSource},
     config::{CustomTestGroup, TestGroup},
-    platform::{BuildPlatforms, BuildPlatformsTarget},
+    platform::{BuildPlatforms, HostPlatform, PlatformLibdir, TargetPlatform},
 };
 use camino::{Utf8Path, Utf8PathBuf};
 use guppy::{
@@ -85,17 +85,19 @@ pub(super) fn binary_query<'a>(
 
 pub(super) fn build_platforms() -> BuildPlatforms {
     BuildPlatforms {
-        host: Platform::new("x86_64-unknown-linux-gnu", TargetFeatures::Unknown).unwrap(),
-        host_libdir: Some(
-            Utf8PathBuf::from("/home/fake/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib")
-        ),
-        target: Some(BuildPlatformsTarget {
+        host: HostPlatform {
+            platform: Platform::new("x86_64-unknown-linux-gnu", TargetFeatures::Unknown).unwrap(),
+            libdir: PlatformLibdir::Available(
+                Utf8PathBuf::from("/home/fake/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib")
+            ),
+        },
+        target: Some(TargetPlatform {
             triple: TargetTriple {
                 platform: Platform::new("aarch64-apple-darwin", TargetFeatures::Unknown).unwrap(),
                 source: TargetTripleSource::Env,
                 location: TargetDefinitionLocation::Builtin,
             },
-            libdir: Some(
+            libdir: PlatformLibdir::Available(
                 Utf8PathBuf::from("/home/fake/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/aarch64-apple-darwin/lib")
             ),
         }),

nextest-runner/src/list/binary_list.rs

@@ -394,10 +394,11 @@ mod tests {
     use crate::{
         cargo_config::{TargetDefinitionLocation, TargetTriple, TargetTripleSource},
         list::SerializableFormat,
-        platform::BuildPlatformsTarget,
+        platform::{HostPlatform, PlatformLibdir, TargetPlatform},
     };
     use indoc::indoc;
     use maplit::btreeset;
+    use nextest_metadata::PlatformLibdirUnavailable;
     use pretty_assertions::assert_eq;
     use target_spec::{Platform, TargetFeatures};
 
@@ -428,13 +429,15 @@ mod tests {
             location: TargetDefinitionLocation::Builtin,
         };
         let fake_host_libdir = "/home/fake/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib";
-        let fake_target_libdir = "/home/fake/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/aarch64-unknown-linux-gnu/lib";
         let build_platforms = BuildPlatforms {
-            host: TargetTriple::x86_64_unknown_linux_gnu().platform,
-            host_libdir: Some(Utf8PathBuf::from(fake_host_libdir)),
-            target: Some(BuildPlatformsTarget {
+            host: HostPlatform {
+                platform: TargetTriple::x86_64_unknown_linux_gnu().platform,
+                libdir: PlatformLibdir::Available(Utf8PathBuf::from(fake_host_libdir)),
+            },
+            target: Some(TargetPlatform {
                 triple: fake_triple,
-                libdir: Some(Utf8PathBuf::from(fake_target_libdir)),
+                // Test out the error case for unavailable libdirs.
+                libdir: PlatformLibdir::Unavailable(PlatformLibdirUnavailable::RUSTC_OUTPUT_ERROR),
             }),
         };
 
@@ -515,15 +518,21 @@ mod tests {
                   "triple": "x86_64-unknown-linux-gnu",
                   "target-features": "unknown"
                 },
-                "libdir": "/home/fake/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib"
+                "libdir": {
+                  "status": "available",
+                  "path": "/home/fake/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib"
+                }
               },
               "targets": [
                 {
                   "platform": {
                     "triple": "aarch64-unknown-linux-gnu",
                     "target-features": "unknown"
                   },
-                  "libdir": "/home/fake/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/aarch64-unknown-linux-gnu/lib"
+                  "libdir": {
+                    "status": "unavailable",
+                    "reason": "rustc-output-error"
+                  }
                 }
               ]
             },