compiletest: set the dylib path when gathering target cfg

If the compiler is built with `rpath = false`, then it won't find its
own libraries unless the library search path is set. We already do that
while running the actual compiletests, but #100260 added another rustc
command for getting the target cfg.

    Check compiletest suite=codegen mode=codegen (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
    thread 'main' panicked at 'error: failed to get cfg info from "[...]/build/x86_64-unknown-linux-gnu/stage1/bin/rustc"
    --- stdout

    --- stderr
    [...]/build/x86_64-unknown-linux-gnu/stage1/bin/rustc: error while loading shared libraries: librustc_driver-a2a76dc626cd02d2.so: cannot open shared object file: No such file or directory
    ', src/tools/compiletest/src/common.rs:476:13

Now the library path is set here as well, so it works without rpath.

src/tools/compiletest/src/common.rs

@@ -2,11 +2,12 @@ pub use self::Mode::*;
 
 use std::ffi::OsString;
 use std::fmt;
+use std::iter;
 use std::path::{Path, PathBuf};
 use std::process::Command;
 use std::str::FromStr;
 
-use crate::util::PathBufExt;
+use crate::util::{add_dylib_path, PathBufExt};
 use lazycell::LazyCell;
 use test::ColorConfig;
 
@@ -385,8 +386,7 @@ impl Config {
     }
 
     fn target_cfg(&self) -> &TargetCfg {
-        self.target_cfg
-            .borrow_with(|| TargetCfg::new(&self.rustc_path, &self.target, &self.target_rustcflags))
+        self.target_cfg.borrow_with(|| TargetCfg::new(self))
     }
 
     pub fn matches_arch(&self, arch: &str) -> bool {
@@ -457,21 +457,23 @@ pub enum Endian {
 }
 
 impl TargetCfg {
-    fn new(rustc_path: &Path, target: &str, target_rustcflags: &Vec<String>) -> TargetCfg {
-        let output = match Command::new(rustc_path)
+    fn new(config: &Config) -> TargetCfg {
+        let mut command = Command::new(&config.rustc_path);
+        add_dylib_path(&mut command, iter::once(&config.compile_lib_path));
+        let output = match command
             .arg("--print=cfg")
             .arg("--target")
-            .arg(target)
-            .args(target_rustcflags)
+            .arg(&config.target)
+            .args(&config.target_rustcflags)
             .output()
         {
             Ok(output) => output,
-            Err(e) => panic!("error: failed to get cfg info from {:?}: {e}", rustc_path),
+            Err(e) => panic!("error: failed to get cfg info from {:?}: {e}", config.rustc_path),
         };
         if !output.status.success() {
             panic!(
                 "error: failed to get cfg info from {:?}\n--- stdout\n{}\n--- stderr\n{}",
-                rustc_path,
+                config.rustc_path,
                 String::from_utf8(output.stdout).unwrap(),
                 String::from_utf8(output.stderr).unwrap(),
             );

src/tools/compiletest/src/runtest.rs

@@ -13,7 +13,7 @@ use crate::errors::{self, Error, ErrorKind};
 use crate::header::TestProps;
 use crate::json;
 use crate::read2::read2_abbreviated;
-use crate::util::{logv, PathBufExt};
+use crate::util::{add_dylib_path, dylib_env_var, logv, PathBufExt};
 use crate::ColorConfig;
 use regex::{Captures, Regex};
 use rustfix::{apply_suggestions, get_suggestions_from_json, Filter};
@@ -26,6 +26,7 @@ use std::fs::{self, create_dir_all, File, OpenOptions};
 use std::hash::{Hash, Hasher};
 use std::io::prelude::*;
 use std::io::{self, BufReader};
+use std::iter;
 use std::path::{Path, PathBuf};
 use std::process::{Child, Command, ExitStatus, Output, Stdio};
 use std::str;
@@ -72,19 +73,6 @@ fn disable_error_reporting<F: FnOnce() -> R, R>(f: F) -> R {
     f()
 }
 
-/// The name of the environment variable that holds dynamic library locations.
-pub fn dylib_env_var() -> &'static str {
-    if cfg!(windows) {
-        "PATH"
-    } else if cfg!(target_os = "macos") {
-        "DYLD_LIBRARY_PATH"
-    } else if cfg!(target_os = "haiku") {
-        "LIBRARY_PATH"
-    } else {
-        "LD_LIBRARY_PATH"
-    }
-}
-
 /// The platform-specific library name
 pub fn get_lib_name(lib: &str, dylib: bool) -> String {
     // In some casess (e.g. MUSL), we build a static
@@ -1811,16 +1799,7 @@ impl<'test> TestCx<'test> {
 
         // Need to be sure to put both the lib_path and the aux path in the dylib
         // search path for the child.
-        let mut path =
-            env::split_paths(&env::var_os(dylib_env_var()).unwrap_or_default()).collect::<Vec<_>>();
-        if let Some(p) = aux_path {
-            path.insert(0, PathBuf::from(p))
-        }
-        path.insert(0, PathBuf::from(lib_path));
-
-        // Add the new dylib search path var
-        let newpath = env::join_paths(&path).unwrap();
-        command.env(dylib_env_var(), newpath);
+        add_dylib_path(&mut command, iter::once(lib_path).chain(aux_path));
 
         let mut child = disable_error_reporting(|| command.spawn())
             .unwrap_or_else(|_| panic!("failed to exec `{:?}`", &command));

src/tools/compiletest/src/util.rs

@@ -2,6 +2,7 @@ use crate::common::Config;
 use std::env;
 use std::ffi::OsStr;
 use std::path::PathBuf;
+use std::process::Command;
 
 use tracing::*;
 
@@ -111,3 +112,25 @@ impl PathBufExt for PathBuf {
         }
     }
 }
+
+/// The name of the environment variable that holds dynamic library locations.
+pub fn dylib_env_var() -> &'static str {
+    if cfg!(windows) {
+        "PATH"
+    } else if cfg!(target_os = "macos") {
+        "DYLD_LIBRARY_PATH"
+    } else if cfg!(target_os = "haiku") {
+        "LIBRARY_PATH"
+    } else {
+        "LD_LIBRARY_PATH"
+    }
+}
+
+/// Adds a list of lookup paths to `cmd`'s dynamic library lookup path.
+/// If the dylib_path_var is already set for this cmd, the old value will be overwritten!
+pub fn add_dylib_path(cmd: &mut Command, paths: impl Iterator<Item = impl Into<PathBuf>>) {
+    let path_env = env::var_os(dylib_env_var());
+    let old_paths = path_env.as_ref().map(env::split_paths);
+    let new_paths = paths.map(Into::into).chain(old_paths.into_iter().flatten());
+    cmd.env(dylib_env_var(), env::join_paths(new_paths).unwrap());
+}