Auto merge of #128370 - petrochenkov:libsearch, r=bjorn3

linker: Pass fewer search directories to the linker

- The logic for passing `-L` directories to the linker is consolidated in a single function, so the search priorities are immediately clear.
- Only `-Lnative=`, `-Lframework=` `-Lall=` directories are passed to linker, but not `-Lcrate=` and others. That's because only native libraries are looked up by name by linker, all Rust crates are passed using full paths, and their directories should not interfere with linker search paths.
- The main sysroot library directory shouldn't generally be passed because it shouldn't contain native libraries, except for one case which is now marked with a FIXME.
- This also helps with #123436, in which we need to walk the same list of directories manually.

The next step is to migrate `find_native_static_library` to exactly the same set and order of search directories (which may be a bit annoying for the `iOSSupport` directories #121430 (comment)).

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -2065,17 +2065,57 @@ fn add_local_crate_metadata_objects(
 }
 
 /// Add sysroot and other globally set directories to the directory search list.
-fn add_library_search_dirs(cmd: &mut dyn Linker, sess: &Session, self_contained: bool) {
-    // The default library location, we need this to find the runtime.
-    // The location of crates will be determined as needed.
-    let lib_path = sess.target_filesearch(PathKind::All).get_lib_path();
-    cmd.include_path(&fix_windows_verbatim_for_gcc(&lib_path));
+fn add_library_search_dirs(
+    cmd: &mut dyn Linker,
+    sess: &Session,
+    self_contained_components: LinkSelfContainedComponents,
+    apple_sdk_root: Option<&Path>,
+) {
+    if !sess.opts.unstable_opts.link_native_libraries {
+        return;
+    }
 
-    // Special directory with libraries used only in self-contained linkage mode
-    if self_contained {
-        let lib_path = sess.target_filesearch(PathKind::All).get_self_contained_lib_path();
+    // Library search paths explicitly supplied by user (`-L` on the command line).
+    for search_path in sess.target_filesearch(PathKind::Native).cli_search_paths() {
+        cmd.include_path(&fix_windows_verbatim_for_gcc(&search_path.dir));
+    }
+    for search_path in sess.target_filesearch(PathKind::Framework).cli_search_paths() {
+        // Contrary to the `-L` docs only framework-specific paths are considered here.
+        if search_path.kind != PathKind::All {
+            cmd.framework_path(&search_path.dir);
+        }
+    }
+
+    // The toolchain ships some native library components and self-contained linking was enabled.
+    // Add the self-contained library directory to search paths.
+    if self_contained_components.intersects(
+        LinkSelfContainedComponents::LIBC
+            | LinkSelfContainedComponents::UNWIND
+            | LinkSelfContainedComponents::MINGW,
+    ) {
+        let lib_path = sess.target_filesearch(PathKind::Native).get_self_contained_lib_path();
         cmd.include_path(&fix_windows_verbatim_for_gcc(&lib_path));
     }
+
+    // Toolchains for some targets may ship `libunwind.a`, but place it into the main sysroot
+    // library directory instead of the self-contained directories.
+    // The targets here should be in sync with `copy_third_party_objects` in bootstrap.
+    // FIXME: implement `-Clink-self-contained=+/-unwind`, move the shipped libunwind
+    // to self-contained directory, and stop adding this search path.
+    if sess.target.vendor == "fortanix" || sess.target.os == "linux" || sess.target.os == "fuchsia"
+    {
+        let lib_path = sess.target_filesearch(PathKind::Native).get_lib_path();
+        cmd.include_path(&fix_windows_verbatim_for_gcc(&lib_path));
+    }
+
+    // Mac Catalyst uses the macOS SDK, but to link to iOS-specific frameworks
+    // we must have the support library stubs in the library search path (#121430).
+    if let Some(sdk_root) = apple_sdk_root
+        && sess.target.llvm_target.contains("macabi")
+    {
+        cmd.include_path(&sdk_root.join("System/iOSSupport/usr/lib"));
+        cmd.framework_path(&sdk_root.join("System/iOSSupport/System/Library/Frameworks"));
+    }
 }
 
 /// Add options making relocation sections in the produced ELF files read-only
@@ -2367,7 +2407,7 @@ fn add_order_independent_options(
     // Take care of the flavors and CLI options requesting the `lld` linker.
     add_lld_args(cmd, sess, flavor, self_contained_components);
 
-    add_apple_sdk(cmd, sess, flavor);
+    let apple_sdk_root = add_apple_sdk(cmd, sess, flavor);
 
     add_link_script(cmd, sess, tmpdir, crate_type);
 
@@ -2423,7 +2463,7 @@ fn add_order_independent_options(
 
     cmd.linker_plugin_lto();
 
-    add_library_search_dirs(cmd, sess, self_contained_components.are_any_components_enabled());
+    add_library_search_dirs(cmd, sess, self_contained_components, apple_sdk_root.as_deref());
 
     cmd.output_filename(out_filename);
 
@@ -2637,19 +2677,6 @@ fn add_local_native_libraries(
     tmpdir: &Path,
     link_output_kind: LinkOutputKind,
 ) {
-    if sess.opts.unstable_opts.link_native_libraries {
-        // User-supplied library search paths (-L on the command line). These are the same paths
-        // used to find Rust crates, so some of them may have been added already by the previous
-        // crate linking code. This only allows them to be found at compile time so it is still
-        // entirely up to outside forces to make sure that library can be found at runtime.
-        for search_path in sess.target_filesearch(PathKind::All).search_paths() {
-            match search_path.kind {
-                PathKind::Framework => cmd.framework_path(&search_path.dir),
-                _ => cmd.include_path(&fix_windows_verbatim_for_gcc(&search_path.dir)),
-            }
-        }
-    }
-
     // All static and dynamic native library dependencies are linked to the local crate.
     let link_static = true;
     let link_dynamic = true;
@@ -2944,19 +2971,19 @@ pub(crate) fn are_upstream_rust_objects_already_included(sess: &Session) -> bool
     }
 }
 
-fn add_apple_sdk(cmd: &mut dyn Linker, sess: &Session, flavor: LinkerFlavor) {
+fn add_apple_sdk(cmd: &mut dyn Linker, sess: &Session, flavor: LinkerFlavor) -> Option<PathBuf> {
     let arch = &sess.target.arch;
     let os = &sess.target.os;
     let llvm_target = &sess.target.llvm_target;
     if sess.target.vendor != "apple"
         || !matches!(os.as_ref(), "ios" | "tvos" | "watchos" | "visionos" | "macos")
         || !matches!(flavor, LinkerFlavor::Darwin(..))
     {
-        return;
+        return None;
     }
 
     if os == "macos" && !matches!(flavor, LinkerFlavor::Darwin(Cc::No, _)) {
-        return;
+        return None;
     }
 
     let sdk_name = match (arch.as_ref(), os.as_ref()) {
@@ -2980,14 +3007,14 @@ fn add_apple_sdk(cmd: &mut dyn Linker, sess: &Session, flavor: LinkerFlavor) {
         (_, "macos") => "macosx",
         _ => {
             sess.dcx().emit_err(errors::UnsupportedArch { arch, os });
-            return;
+            return None;
         }
     };
     let sdk_root = match get_apple_sdk_root(sdk_name) {
         Ok(s) => s,
         Err(e) => {
             sess.dcx().emit_err(e);
-            return;
+            return None;
         }
     };
 
@@ -3007,16 +3034,7 @@ fn add_apple_sdk(cmd: &mut dyn Linker, sess: &Session, flavor: LinkerFlavor) {
         _ => unreachable!(),
     }
 
-    if llvm_target.contains("macabi") {
-        // Mac Catalyst uses the macOS SDK, but to link to iOS-specific
-        // frameworks, we must have the support library stubs in the library
-        // search path.
-
-        // The flags are called `-L` and `-F` both in Clang, ld64 and ldd.
-        let sdk_root = Path::new(&sdk_root);
-        cmd.include_path(&sdk_root.join("System/iOSSupport/usr/lib"));
-        cmd.framework_path(&sdk_root.join("System/iOSSupport/System/Library/Frameworks"));
-    }
+    Some(sdk_root.into())
 }
 
 fn get_apple_sdk_root(sdk_name: &str) -> Result<String, errors::AppleSdkRootError<'_>> {

compiler/rustc_session/src/filesearch.rs

@@ -19,6 +19,11 @@ pub struct FileSearch<'a> {
 }
 
 impl<'a> FileSearch<'a> {
+    pub fn cli_search_paths(&self) -> impl Iterator<Item = &'a SearchPath> {
+        let kind = self.kind;
+        self.cli_search_paths.iter().filter(move |sp| sp.kind.matches(kind))
+    }
+
     pub fn search_paths(&self) -> impl Iterator<Item = &'a SearchPath> {
         let kind = self.kind;
         self.cli_search_paths