Link `std` statically in `rustc_driver`

2 files changed, 33 insertions, 6 deletions

diff --git a/compiler/rustc/src/main.rs b/compiler/rustc/src/main.rs
index 29766fc9d87..e9a7397557e 100644
--- a/compiler/rustc/src/main.rs
+++ b/compiler/rustc/src/main.rs
@@ -1,3 +1,6 @@
+// We need this feature as it changes `dylib` linking behavior and allows us to link to `rustc_driver`.
+#![feature(rustc_private)]
+
 // A note about jemalloc: rustc uses jemalloc when built for CI and
 // distribution. The obvious way to do this is with the `#[global_allocator]`
 // mechanism. However, for complicated reasons (see
diff --git a/compiler/rustc_metadata/src/dependency_format.rs b/compiler/rustc_metadata/src/dependency_format.rs
index 17fd260fd79..95b1a40d892 100644
--- a/compiler/rustc_metadata/src/dependency_format.rs
+++ b/compiler/rustc_metadata/src/dependency_format.rs
@@ -51,7 +51,7 @@
 //! Additionally, the algorithm is geared towards finding *any* solution rather
 //! than finding a number of solutions (there are normally quite a few).
 
-use rustc_data_structures::fx::FxHashMap;
+use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_hir::def_id::CrateNum;
 use rustc_middle::bug;
 use rustc_middle::middle::dependency_format::{Dependencies, DependencyList, Linkage};
@@ -160,18 +160,43 @@ fn calculate_type(tcx: TyCtxt<'_>, ty: CrateType) -> DependencyList {
         Linkage::Dynamic | Linkage::IncludedFromDylib => {}
     }
 
+    let all_dylibs = || {
+        tcx.crates(()).iter().filter(|&&cnum| {
+            !tcx.dep_kind(cnum).macros_only() && tcx.used_crate_source(cnum).dylib.is_some()
+        })
+    };
+
+    let mut upstream_in_dylibs = FxHashSet::default();
+
+    if tcx.features().rustc_private {
+        // We need this to prevent users of `rustc_driver` from linking dynamically to `std`
+        // which does not work as `std` is also statically linked into `rustc_driver`.
+
+        // Find all libraries statically linked to upstream dylibs.
+        for &cnum in all_dylibs() {
+            let deps = tcx.dylib_dependency_formats(cnum);
+            for &(depnum, style) in deps.iter() {
+                if let RequireStatic = style {
+                    upstream_in_dylibs.insert(depnum);
+                }
+            }
+        }
+    }
+
     let mut formats = FxHashMap::default();
 
     // Sweep all crates for found dylibs. Add all dylibs, as well as their
     // dependencies, ensuring there are no conflicts. The only valid case for a
     // dependency to be relied upon twice is for both cases to rely on a dylib.
-    for &cnum in tcx.crates(()).iter() {
-        if tcx.dep_kind(cnum).macros_only() {
+    for &cnum in all_dylibs() {
+        if upstream_in_dylibs.contains(&cnum) {
+            info!("skipping dylib: {}", tcx.crate_name(cnum));
+            // If this dylib is also available statically linked to another dylib
+            // we try to use that instead.
             continue;
         }
+
         let name = tcx.crate_name(cnum);
-        let src = tcx.used_crate_source(cnum);
-        if src.dylib.is_some() {
             info!("adding dylib: {}", name);
             add_library(tcx, cnum, RequireDynamic, &mut formats, &mut unavailable_as_static);
             let deps = tcx.dylib_dependency_formats(cnum);
@@ -180,7 +205,6 @@ fn calculate_type(tcx: TyCtxt<'_>, ty: CrateType) -> DependencyList {
                 add_library(tcx, depnum, style, &mut formats, &mut unavailable_as_static);
             }
         }
-    }
 
     // Collect what we've got so far in the return vector.
     let last_crate = tcx.crates(()).len();