check host's libstdc++ version when using ci llvm

Signed-off-by: onur-ozkan <work@onurozkan.dev>

Author: onur-ozkan

src/bootstrap/src/core/build_steps/tool.rs

@@ -10,6 +10,7 @@ use crate::core::builder::{Builder, Cargo as CargoCommand, RunConfig, ShouldRun,
 use crate::core::config::TargetSelection;
 use crate::utils::channel::GitInfo;
 use crate::utils::exec::BootstrapCommand;
+use crate::utils::helpers::output;
 use crate::utils::helpers::{add_dylib_path, exe, t};
 use crate::Compiler;
 use crate::Mode;
@@ -804,6 +805,59 @@ impl Step for LlvmBitcodeLinker {
     }
 }
 
+#[derive(Debug, Clone, Hash, PartialEq, Eq)]
+pub struct LibcxxVersionTool {
+    pub target: TargetSelection,
+}
+
+#[derive(Debug, Clone)]
+pub enum LibcxxVersion {
+    Gnu(usize),
+    #[allow(dead_code)]
+    Llvm(usize),
+}
+
+impl Step for LibcxxVersionTool {
+    type Output = LibcxxVersion;
+    const DEFAULT: bool = false;
+    const ONLY_HOSTS: bool = true;
+
+    fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
+        run.never()
+    }
+
+    fn run(self, builder: &Builder<'_>) -> LibcxxVersion {
+        let out_dir = builder.out.join(self.target.to_string()).join("libcxx-version");
+        let _ = fs::remove_dir_all(&out_dir);
+        t!(fs::create_dir_all(&out_dir));
+
+        let compiler = builder.cxx(self.target).unwrap();
+        let mut cmd = Command::new(compiler);
+
+        let executable = out_dir.join("libcxx-version");
+        cmd.arg("-o").arg(&executable).arg(builder.src.join("src/tools/libcxx-version/main.cpp"));
+
+        builder.run_cmd(&mut cmd);
+
+        if !executable.exists() {
+            panic!("Something went wrong. {} is not present", executable.display());
+        }
+
+        let version_output = output(&mut Command::new(executable));
+
+        let version_str = version_output.split_once("version:").unwrap().1;
+        let version = version_str.trim().parse::<usize>().unwrap();
+
+        if version_output.starts_with("libstdc++") {
+            LibcxxVersion::Gnu(version)
+        } else if version_output.starts_with("libc++") {
+            LibcxxVersion::Llvm(version)
+        } else {
+            panic!("Coudln't recognize the standard library version.");
+        }
+    }
+}
+
 macro_rules! tool_extended {
     (($sel:ident, $builder:ident),
        $($name:ident,

src/bootstrap/src/core/sanity.rs

@@ -18,7 +18,8 @@ use std::process::Command;
 #[cfg(not(feature = "bootstrap-self-test"))]
 use std::collections::HashSet;
 
-use crate::builder::Kind;
+use crate::builder::{Builder, Kind};
+use crate::core::build_steps::tool;
 use crate::core::config::Target;
 use crate::utils::helpers::output;
 use crate::Build;
@@ -38,6 +39,10 @@ const STAGE0_MISSING_TARGETS: &[&str] = &[
     // just a dummy comment so the list doesn't get onelined
 ];
 
+/// Minimum version threshold for libstdc++ required when using prebuilt LLVM
+/// from CI (with`llvm.download-ci-llvm` option).
+const LIBSTDCXX_MIN_VERSION_THRESHOLD: usize = 8;
+
 impl Finder {
     pub fn new() -> Self {
         Self { cache: HashMap::new(), path: env::var_os("PATH").unwrap_or_default() }
@@ -102,6 +107,35 @@ pub fn check(build: &mut Build) {
         cmd_finder.must_have("git");
     }
 
+    // Ensure that a compatible version of libstdc++ is available on the system when using `llvm.download-ci-llvm`.
+    if !build.config.dry_run() && !build.build.is_msvc() && build.config.llvm_from_ci {
+        let builder = Builder::new(build);
+        let libcxx_version = builder.ensure(tool::LibcxxVersionTool { target: build.build });
+
+        match libcxx_version {
+            tool::LibcxxVersion::Gnu(version) => {
+                if LIBSTDCXX_MIN_VERSION_THRESHOLD > version {
+                    eprintln!(
+                        "\nYour system's libstdc++ version is too old for the `llvm.download-ci-llvm` option."
+                    );
+                    eprintln!("Current version detected: '{}'", version);
+                    eprintln!("Minimum required version: '{}'", LIBSTDCXX_MIN_VERSION_THRESHOLD);
+                    eprintln!(
+                        "Consider upgrading libstdc++ or disabling the `llvm.download-ci-llvm` option."
+                    );
+                    crate::exit!(1);
+                }
+            }
+            tool::LibcxxVersion::Llvm(_) => {
+                eprintln!(
+                    "\nYour system is using libc++, which is incompatible with the `llvm.download-ci-llvm` option."
+                );
+                eprintln!("Disable `llvm.download-ci-llvm` or switch to libstdc++.");
+                crate::exit!(1);
+            }
+        }
+    }
+
     // We need cmake, but only if we're actually building LLVM or sanitizers.
     let building_llvm = build
         .hosts