Rollup merge of #70123 - cuviper:library-path, r=Mark-Simulacrum

Ensure LLVM is in the link path for rustc tools

The build script for `rustc_llvm` outputs LLVM information in `cargo:rustc-link-lib` and `cargo:rustc-link-search` so the compiler can be linked correctly. However, while the lib is carried along in metadata, the search paths are not. So when cargo is invoked again later for rustc _tools_, they'll also try to link with LLVM, but the necessary paths may be left out.

Rustbuild can use the environment to set the LLVM link path for tools -- `LIB` for MSVC toolchains and `LIBRARY_PATH` for everyone else.

Fixes #68714.

src/bootstrap/builder.rs

@@ -11,7 +11,7 @@ use std::path::{Path, PathBuf};
 use std::process::Command;
 use std::time::{Duration, Instant};
 
-use build_helper::t;
+use build_helper::{output, t};
 
 use crate::cache::{Cache, Interned, INTERNER};
 use crate::check;
@@ -23,7 +23,7 @@ use crate::install;
 use crate::native;
 use crate::test;
 use crate::tool;
-use crate::util::{self, add_lib_path, exe, libdir};
+use crate::util::{self, add_dylib_path, add_link_lib_path, exe, libdir};
 use crate::{Build, DocTests, GitRepo, Mode};
 
 pub use crate::Compiler;
@@ -660,7 +660,7 @@ impl<'a> Builder<'a> {
             return;
         }
 
-        add_lib_path(vec![self.rustc_libdir(compiler)], &mut cmd.command);
+        add_dylib_path(vec![self.rustc_libdir(compiler)], &mut cmd.command);
     }
 
     /// Gets a path to the compiler specified.
@@ -698,6 +698,20 @@ impl<'a> Builder<'a> {
         cmd
     }
 
+    /// Return the path to `llvm-config` for the target, if it exists.
+    ///
+    /// Note that this returns `None` if LLVM is disabled, or if we're in a
+    /// check build or dry-run, where there's no need to build all of LLVM.
+    fn llvm_config(&self, target: Interned<String>) -> Option<PathBuf> {
+        if self.config.llvm_enabled() && self.kind != Kind::Check && !self.config.dry_run {
+            let llvm_config = self.ensure(native::Llvm { target });
+            if llvm_config.is_file() {
+                return Some(llvm_config);
+            }
+        }
+        None
+    }
+
     /// Prepares an invocation of `cargo` to be run.
     ///
     /// This will create a `Command` that represents a pending execution of
@@ -1034,6 +1048,17 @@ impl<'a> Builder<'a> {
                 .env("RUSTC_SNAPSHOT_LIBDIR", self.rustc_libdir(compiler));
         }
 
+        // Tools that use compiler libraries may inherit the `-lLLVM` link
+        // requirement, but the `-L` library path is not propagated across
+        // separate Cargo projects. We can add LLVM's library path to the
+        // platform-specific environment variable as a workaround.
+        if mode == Mode::ToolRustc {
+            if let Some(llvm_config) = self.llvm_config(target) {
+                let llvm_libdir = output(Command::new(&llvm_config).arg("--libdir"));
+                add_link_lib_path(vec![llvm_libdir.trim().into()], &mut cargo);
+            }
+        }
+
         if self.config.incremental {
             cargo.env("CARGO_INCREMENTAL", "1");
         } else {

src/bootstrap/compile.rs

@@ -451,44 +451,6 @@ impl Step for Rustc {
             false,
         );
 
-        // We used to build librustc_codegen_llvm as a separate step,
-        // which produced a dylib that the compiler would dlopen() at runtime.
-        // This meant that we only needed to make sure that libLLVM.so was
-        // installed by the time we went to run a tool using it - since
-        // librustc_codegen_llvm was effectively a standalone artifact,
-        // other crates were completely oblivious to its dependency
-        // on `libLLVM.so` during build time.
-        //
-        // However, librustc_codegen_llvm is now built as an ordinary
-        // crate during the same step as the rest of the compiler crates.
-        // This means that any crates depending on it will see the fact
-        // that it uses `libLLVM.so` as a native library, and will
-        // cause us to pass `-llibLLVM.so` to the linker when we link
-        // a binary.
-        //
-        // For `rustc` itself, this works out fine.
-        // During the `Assemble` step, we call `dist::maybe_install_llvm_dylib`
-        // to copy libLLVM.so into the `stage` directory. We then link
-        // the compiler binary, which will find `libLLVM.so` in the correct place.
-        //
-        // However, this is insufficient for tools that are build against stage0
-        // (e.g. stage1 rustdoc). Since `Assemble` for stage0 doesn't actually do anything,
-        // we won't have `libLLVM.so` in the stage0 sysroot. In the past, this wasn't
-        // a problem - we would copy the tool binary into its correct stage directory
-        // (e.g. stage1 for a stage1 rustdoc built against a stage0 compiler).
-        // Since libLLVM.so wasn't resolved until runtime, it was fine for it to
-        // not exist while we were building it.
-        //
-        // To ensure that we can still build stage1 tools against a stage0 compiler,
-        // we explicitly copy libLLVM.so into the stage0 sysroot when building
-        // the stage0 compiler. This ensures that tools built against stage0
-        // will see libLLVM.so at build time, making the linker happy.
-        if compiler.stage == 0 {
-            builder.info(&format!("Installing libLLVM.so to stage 0 ({})", compiler.host));
-            let sysroot = builder.sysroot(compiler);
-            dist::maybe_install_llvm_dylib(builder, compiler.host, &sysroot);
-        }
-
         builder.ensure(RustcLink {
             compiler: builder.compiler(compiler.stage, builder.config.build),
             target_compiler: compiler,

src/bootstrap/tool.rs

@@ -12,7 +12,7 @@ use crate::channel;
 use crate::channel::GitInfo;
 use crate::compile;
 use crate::toolstate::ToolState;
-use crate::util::{add_lib_path, exe, CiEnv};
+use crate::util::{add_dylib_path, exe, CiEnv};
 use crate::Compiler;
 use crate::Mode;
 
@@ -388,7 +388,7 @@ pub struct ErrorIndex {
 impl ErrorIndex {
     pub fn command(builder: &Builder<'_>, compiler: Compiler) -> Command {
         let mut cmd = Command::new(builder.ensure(ErrorIndex { compiler }));
-        add_lib_path(
+        add_dylib_path(
             vec![PathBuf::from(&builder.sysroot_libdir(compiler, compiler.host))],
             &mut cmd,
         );
@@ -689,7 +689,7 @@ impl<'a> Builder<'a> {
             }
         }
 
-        add_lib_path(lib_paths, &mut cmd);
+        add_dylib_path(lib_paths, &mut cmd);
         cmd
     }
 }

src/bootstrap/util.rs

@@ -40,7 +40,7 @@ pub fn libdir(target: &str) -> &'static str {
 }
 
 /// Adds a list of lookup paths to `cmd`'s dynamic library lookup path.
-pub fn add_lib_path(path: Vec<PathBuf>, cmd: &mut Command) {
+pub fn add_dylib_path(path: Vec<PathBuf>, cmd: &mut Command) {
     let mut list = dylib_path();
     for path in path {
         list.insert(0, path);
@@ -72,6 +72,31 @@ pub fn dylib_path() -> Vec<PathBuf> {
     env::split_paths(&var).collect()
 }
 
+/// Adds a list of lookup paths to `cmd`'s link library lookup path.
+pub fn add_link_lib_path(path: Vec<PathBuf>, cmd: &mut Command) {
+    let mut list = link_lib_path();
+    for path in path {
+        list.insert(0, path);
+    }
+    cmd.env(link_lib_path_var(), t!(env::join_paths(list)));
+}
+
+/// Returns the environment variable which the link library lookup path
+/// resides in for this platform.
+fn link_lib_path_var() -> &'static str {
+    if cfg!(target_env = "msvc") { "LIB" } else { "LIBRARY_PATH" }
+}
+
+/// Parses the `link_lib_path_var()` environment variable, returning a list of
+/// paths that are members of this lookup path.
+fn link_lib_path() -> Vec<PathBuf> {
+    let var = match env::var_os(link_lib_path_var()) {
+        Some(v) => v,
+        None => return vec![],
+    };
+    env::split_paths(&var).collect()
+}
+
 /// `push` all components to `buf`. On windows, append `.exe` to the last component.
 pub fn push_exe_path(mut buf: PathBuf, components: &[&str]) -> PathBuf {
     let (&file, components) = components.split_last().expect("at least one component required");