Rollup merge of rust-lang#145256 - GuillaumeGomez:bootstrap-test-codegen-backend, r=Kobzol,bjorn3

Add new `--test-codegen-backend` bootstrap option

This new bootstrap command line flag allows to do:

```shell
./x.py test tests/ui/intrinsics/panic-uninitialized-zeroed.rs --stage 1 -j8 --test-codegen-backend gcc
```

This is the last step before running it into the CI.

Supersedes rust-lang#144687.

r? ````@Kobzol````

Author: jhpratt

src/bootstrap/src/core/build_steps/test.rs

@@ -1830,10 +1830,27 @@ NOTE: if you're sure you want to do this, please open an issue as to why. In the
         cmd.arg("--host").arg(&*compiler.host.triple);
         cmd.arg("--llvm-filecheck").arg(builder.llvm_filecheck(builder.config.host_target));
 
-        if let Some(codegen_backend) = builder.config.default_codegen_backend(compiler.host) {
-            // Tells compiletest which codegen backend is used by default by the compiler.
+        if let Some(codegen_backend) = builder.config.cmd.test_codegen_backend() {
+            if !builder.config.enabled_codegen_backends(compiler.host).contains(codegen_backend) {
+                eprintln!(
+                    "\
+ERROR: No configured backend named `{name}`
+HELP: You can add it into `bootstrap.toml` in `rust.codegen-backends = [{name:?}]`",
+                    name = codegen_backend.name(),
+                );
+                crate::exit!(1);
+            }
+            // Tells compiletest that we want to use this codegen in particular and to override
+            // the default one.
+            cmd.arg("--override-codegen-backend").arg(codegen_backend.name());
+            // Tells compiletest which codegen backend to use.
+            // It is used to e.g. ignore tests that don't support that codegen backend.
+            cmd.arg("--default-codegen-backend").arg(codegen_backend.name());
+        } else {
+            // Tells compiletest which codegen backend to use.
             // It is used to e.g. ignore tests that don't support that codegen backend.
-            cmd.arg("--codegen-backend").arg(codegen_backend.name());
+            cmd.arg("--default-codegen-backend")
+                .arg(builder.config.default_codegen_backend(compiler.host).unwrap().name());
         }
 
         if builder.build.config.llvm_enzyme {

src/bootstrap/src/core/builder/cargo.rs

@@ -1326,7 +1326,12 @@ impl Builder<'_> {
 
             if let Some(limit) = limit
                 && (build_compiler_stage == 0
-                    || self.config.default_codegen_backend(target).unwrap_or_default().is_llvm())
+                    || self
+                        .config
+                        .default_codegen_backend(target)
+                        .cloned()
+                        .unwrap_or_default()
+                        .is_llvm())
             {
                 rustflags.arg(&format!("-Cllvm-args=-import-instr-limit={limit}"));
             }

src/bootstrap/src/core/config/config.rs

@@ -1755,8 +1755,8 @@ impl Config {
 
     /// Returns the codegen backend that should be configured as the *default* codegen backend
     /// for a rustc compiled by bootstrap.
-    pub fn default_codegen_backend(&self, target: TargetSelection) -> Option<CodegenBackendKind> {
-        self.enabled_codegen_backends(target).first().cloned()
+    pub fn default_codegen_backend(&self, target: TargetSelection) -> Option<&CodegenBackendKind> {
+        self.enabled_codegen_backends(target).first()
     }
 
     pub fn jemalloc(&self, target: TargetSelection) -> bool {

src/bootstrap/src/core/config/flags.rs

@@ -15,7 +15,7 @@ use crate::core::build_steps::setup::Profile;
 use crate::core::builder::{Builder, Kind};
 use crate::core::config::Config;
 use crate::core::config::target_selection::{TargetSelectionList, target_selection_list};
-use crate::{Build, DocTests};
+use crate::{Build, CodegenBackendKind, DocTests};
 
 #[derive(Copy, Clone, Default, Debug, ValueEnum)]
 pub enum Color {
@@ -419,6 +419,9 @@ pub enum Subcommand {
         #[arg(long)]
         /// don't capture stdout/stderr of tests
         no_capture: bool,
+        #[arg(long)]
+        /// Use a different codegen backend when running tests.
+        test_codegen_backend: Option<CodegenBackendKind>,
     },
     /// Build and run some test suites *in Miri*
     Miri {
@@ -658,6 +661,13 @@ impl Subcommand {
             _ => vec![],
         }
     }
+
+    pub fn test_codegen_backend(&self) -> Option<&CodegenBackendKind> {
+        match self {
+            Subcommand::Test { test_codegen_backend, .. } => test_codegen_backend.as_ref(),
+            _ => None,
+        }
+    }
 }
 
 /// Returns the shell completion for a given shell, if the result differs from the current

src/bootstrap/src/lib.rs

@@ -165,6 +165,20 @@ impl CodegenBackendKind {
     }
 }
 
+impl std::str::FromStr for CodegenBackendKind {
+    type Err = &'static str;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        match s.to_lowercase().as_str() {
+            "" => Err("Invalid empty backend name"),
+            "gcc" => Ok(Self::Gcc),
+            "llvm" => Ok(Self::Llvm),
+            "cranelift" => Ok(Self::Cranelift),
+            _ => Ok(Self::Custom(s.to_string())),
+        }
+    }
+}
+
 #[derive(PartialEq, Eq, Copy, Clone, Debug)]
 pub enum DocTests {
     /// Run normal tests and doc tests (default).

src/bootstrap/src/utils/change_tracker.rs

@@ -506,6 +506,11 @@ pub const CONFIG_CHANGE_HISTORY: &[ChangeInfo] = &[
         severity: ChangeSeverity::Warning,
         summary: "It is no longer possible to `x clippy` with stage 0. All clippy commands have to be on stage 1+.",
     },
+    ChangeInfo {
+        change_id: 145256,
+        severity: ChangeSeverity::Info,
+        summary: "Added `--test-codegen-backend` CLI option for tests",
+    },
     ChangeInfo {
         change_id: 145379,
         severity: ChangeSeverity::Info,

src/etc/completions/x.fish

@@ -305,6 +305,7 @@ complete -c x -n "__fish_x_using_subcommand test" -l extra-checks -d 'comma-sepa
 complete -c x -n "__fish_x_using_subcommand test" -l compare-mode -d 'mode describing what file the actual ui output will be compared to' -r
 complete -c x -n "__fish_x_using_subcommand test" -l pass -d 'force {check,build,run}-pass tests to this mode' -r
 complete -c x -n "__fish_x_using_subcommand test" -l run -d 'whether to execute run-* tests' -r
+complete -c x -n "__fish_x_using_subcommand test" -l test-codegen-backend -d 'Use a different codegen backend when running tests' -r
 complete -c x -n "__fish_x_using_subcommand test" -l config -d 'TOML configuration file for build' -r -F
 complete -c x -n "__fish_x_using_subcommand test" -l build-dir -d 'Build directory, overrides `build.build-dir` in `bootstrap.toml`' -r -f -a "(__fish_complete_directories)"
 complete -c x -n "__fish_x_using_subcommand test" -l build -d 'host target of the stage0 compiler' -r -f

src/etc/completions/x.ps1

@@ -351,6 +351,7 @@ Register-ArgumentCompleter -Native -CommandName 'x' -ScriptBlock {
             [CompletionResult]::new('--compare-mode', '--compare-mode', [CompletionResultType]::ParameterName, 'mode describing what file the actual ui output will be compared to')
             [CompletionResult]::new('--pass', '--pass', [CompletionResultType]::ParameterName, 'force {check,build,run}-pass tests to this mode')
             [CompletionResult]::new('--run', '--run', [CompletionResultType]::ParameterName, 'whether to execute run-* tests')
+            [CompletionResult]::new('--test-codegen-backend', '--test-codegen-backend', [CompletionResultType]::ParameterName, 'Use a different codegen backend when running tests')
             [CompletionResult]::new('--config', '--config', [CompletionResultType]::ParameterName, 'TOML configuration file for build')
             [CompletionResult]::new('--build-dir', '--build-dir', [CompletionResultType]::ParameterName, 'Build directory, overrides `build.build-dir` in `bootstrap.toml`')
             [CompletionResult]::new('--build', '--build', [CompletionResultType]::ParameterName, 'host target of the stage0 compiler')

src/etc/completions/x.py.fish

@@ -305,6 +305,7 @@ complete -c x.py -n "__fish_x.py_using_subcommand test" -l extra-checks -d 'comm
 complete -c x.py -n "__fish_x.py_using_subcommand test" -l compare-mode -d 'mode describing what file the actual ui output will be compared to' -r
 complete -c x.py -n "__fish_x.py_using_subcommand test" -l pass -d 'force {check,build,run}-pass tests to this mode' -r
 complete -c x.py -n "__fish_x.py_using_subcommand test" -l run -d 'whether to execute run-* tests' -r
+complete -c x.py -n "__fish_x.py_using_subcommand test" -l test-codegen-backend -d 'Use a different codegen backend when running tests' -r
 complete -c x.py -n "__fish_x.py_using_subcommand test" -l config -d 'TOML configuration file for build' -r -F
 complete -c x.py -n "__fish_x.py_using_subcommand test" -l build-dir -d 'Build directory, overrides `build.build-dir` in `bootstrap.toml`' -r -f -a "(__fish_complete_directories)"
 complete -c x.py -n "__fish_x.py_using_subcommand test" -l build -d 'host target of the stage0 compiler' -r -f

src/etc/completions/x.py.ps1

@@ -351,6 +351,7 @@ Register-ArgumentCompleter -Native -CommandName 'x.py' -ScriptBlock {
             [CompletionResult]::new('--compare-mode', '--compare-mode', [CompletionResultType]::ParameterName, 'mode describing what file the actual ui output will be compared to')
             [CompletionResult]::new('--pass', '--pass', [CompletionResultType]::ParameterName, 'force {check,build,run}-pass tests to this mode')
             [CompletionResult]::new('--run', '--run', [CompletionResultType]::ParameterName, 'whether to execute run-* tests')
+            [CompletionResult]::new('--test-codegen-backend', '--test-codegen-backend', [CompletionResultType]::ParameterName, 'Use a different codegen backend when running tests')
             [CompletionResult]::new('--config', '--config', [CompletionResultType]::ParameterName, 'TOML configuration file for build')
             [CompletionResult]::new('--build-dir', '--build-dir', [CompletionResultType]::ParameterName, 'Build directory, overrides `build.build-dir` in `bootstrap.toml`')
             [CompletionResult]::new('--build', '--build', [CompletionResultType]::ParameterName, 'host target of the stage0 compiler')