A collection of test cases showing how the new -C prefer-dynamic=crate,... flag can be used to resolve issue 82151.

These differ from the diamonds-*.rs in a couple of ways:
 * The most foundational library is being compiled to multiple crate output types, and
 * The most foundational library is being compiled to a `cdylib`, not a `dylib`.

These two details seemed to be critical for reproducing the exact set of
unfortunate link-time behaviors that we observed on issue 82151, as illustrated
by the family of tests named `issue-82151-serverctl-*.rs`.

----

issue-82151-serverctl-prefdyn.rs works around ld-binary specific details by
adding extra normalization to test, including normalizing stage number in output.

Author: pnkfelix

src/test/ui/dylibs/auxiliary/aaa_issue_82151_bar.rs

@@ -0,0 +1,9 @@
+#![crate_name="bar"]
+#![crate_type="rlib"]
+#![crate_type="cdylib"]
+
+pub struct Bar;
+
+pub fn bar() -> Bar {
+    Bar
+}

src/test/ui/dylibs/auxiliary/aaa_issue_82151_bar_noprefdyn.rs

@@ -0,0 +1,11 @@
+#![crate_name="bar"]
+#![crate_type="rlib"]
+#![crate_type="cdylib"]
+
+// no-prefer-dynamic
+
+pub struct Bar;
+
+pub fn bar() -> Bar {
+    Bar
+}

src/test/ui/dylibs/auxiliary/aaa_issue_82151_bar_prefdyn.rs

@@ -0,0 +1,12 @@
+#![crate_name="bar"]
+#![crate_type="rlib"]
+#![crate_type="cdylib"]
+
+// no-prefer-dynamic
+// compile-flags: -C prefer-dynamic
+
+pub struct Bar;
+
+pub fn bar() -> Bar {
+    Bar
+}

src/test/ui/dylibs/auxiliary/aaa_issue_82151_bar_prefdynstd.rs

@@ -0,0 +1,12 @@
+#![crate_name="bar"]
+#![crate_type="rlib"]
+#![crate_type="cdylib"]
+
+// no-prefer-dynamic
+// compile-flags: -C prefer-dynamic=std -Z prefer-dynamic-std
+
+pub struct Bar;
+
+pub fn bar() -> Bar {
+    Bar
+}

src/test/ui/dylibs/auxiliary/aaa_issue_82151_bar_prefdynsubset.rs

@@ -0,0 +1,12 @@
+#![crate_name="bar"]
+#![crate_type="rlib"]
+#![crate_type="cdylib"]
+
+// no-prefer-dynamic
+// compile-flags: -C prefer-dynamic=shared,std -Z prefer-dynamic-subset
+
+pub struct Bar;
+
+pub fn bar() -> Bar {
+    Bar
+}

src/test/ui/dylibs/auxiliary/aaa_issue_82151_foo_noprefdyn.rs

@@ -0,0 +1,13 @@
+#![crate_name="foo"]
+#![crate_type="rlib"]
+
+// no-prefer-dynamic
+
+extern crate bar;
+
+pub struct Foo;
+pub use bar::bar;
+
+pub fn foo() -> Foo {
+    Foo
+}

src/test/ui/dylibs/auxiliary/aaa_issue_82151_foo_prefdyn.rs

@@ -0,0 +1,14 @@
+#![crate_name="foo"]
+#![crate_type="rlib"]
+
+// no-prefer-dynamic
+// compile-flags: -C prefer-dynamic
+
+extern crate bar;
+
+pub struct Foo;
+pub use bar::bar;
+
+pub fn foo() -> Foo {
+    Foo
+}

src/test/ui/dylibs/auxiliary/aaa_issue_82151_foo_prefdynstd.rs

@@ -0,0 +1,14 @@
+#![crate_name="foo"]
+#![crate_type="rlib"]
+
+// no-prefer-dynamic
+// compile-flags: -C prefer-dynamic=std -Z prefer-dynamic-std
+
+extern crate bar;
+
+pub struct Foo;
+pub use bar::bar;
+
+pub fn foo() -> Foo {
+    Foo
+}

src/test/ui/dylibs/auxiliary/aaa_issue_82151_foo_prefdynsubset.rs

@@ -0,0 +1,14 @@
+#![crate_name="foo"]
+#![crate_type="rlib"]
+
+// no-prefer-dynamic
+// compile-flags: -C prefer-dynamic=shared,std -Z prefer-dynamic-subset
+
+extern crate bar;
+
+pub struct Foo;
+pub use bar::bar;
+
+pub fn foo() -> Foo {
+    Foo
+}

src/test/ui/dylibs/auxiliary/aaa_issue_82151_shared_noprefdyn.rs

@@ -0,0 +1,17 @@
+#![crate_name="shared"]
+#![crate_type="dylib"]
+
+// no-prefer-dynamic
+
+extern crate foo;
+
+pub struct Test;
+
+impl Test {
+    pub fn new() -> Self {
+        let _ = foo::foo();
+        let _ = foo::bar();
+        // let _ = bar::bar();
+        Self
+    }
+}

src/test/ui/dylibs/auxiliary/aaa_issue_82151_shared_prefdyn.rs

@@ -0,0 +1,18 @@
+#![crate_name="shared"]
+#![crate_type="dylib"]
+
+// no-prefer-dynamic
+// compile-flags: -C prefer-dynamic
+
+extern crate foo;
+
+pub struct Test;
+
+impl Test {
+    pub fn new() -> Self {
+        let _ = foo::foo();
+        let _ = foo::bar();
+        // let _ = bar::bar();
+        Self
+    }
+}

src/test/ui/dylibs/auxiliary/aaa_issue_82151_shared_prefdynstd.rs

@@ -0,0 +1,18 @@
+#![crate_name="shared"]
+#![crate_type="dylib"]
+
+// no-prefer-dynamic
+// compile-flags: -C prefer-dynamic=std -Z prefer-dynamic-std
+
+extern crate foo;
+
+pub struct Test;
+
+impl Test {
+    pub fn new() -> Self {
+        let _ = foo::foo();
+        let _ = foo::bar();
+        // let _ = bar::bar();
+        Self
+    }
+}

src/test/ui/dylibs/auxiliary/aaa_issue_82151_shared_prefdynsubset.rs

@@ -0,0 +1,18 @@
+#![crate_name="shared"]
+#![crate_type="dylib"]
+
+// no-prefer-dynamic
+// compile-flags: -C prefer-dynamic=shared,std -Z prefer-dynamic-subset
+
+extern crate foo;
+
+pub struct Test;
+
+impl Test {
+    pub fn new() -> Self {
+        let _ = foo::foo();
+        let _ = foo::bar();
+        // let _ = bar::bar();
+        Self
+    }
+}

src/test/ui/dylibs/issue-82151-serverctl-noprefdyn.rs

@@ -0,0 +1,13 @@
+// build-fail
+
+// no-prefer-dynamic
+
+// aux-build: aaa_issue_82151_bar_noprefdyn.rs
+// aux-build: aaa_issue_82151_foo_noprefdyn.rs
+// aux-build: aaa_issue_82151_shared_noprefdyn.rs
+
+extern crate shared;
+
+fn main() {
+    let _ = shared::Test::new();
+}

src/test/ui/dylibs/issue-82151-serverctl-noprefdyn.stderr

@@ -0,0 +1,78 @@
+error: cannot satisfy dependencies so `std` only shows up once (previously required dynamic, via [`issue_82151_serverctl_noprefdyn`], and now also requires static, via [`shared`])
+   |
+   = help: having upstream crates all available in one format will likely make this go away
+
+error: cannot satisfy dependencies so `core` only shows up once (two static copies from multiple different locations, via [`std`, `shared`])
+   |
+   = help: having upstream crates all available in one format will likely make this go away
+
+error: cannot satisfy dependencies so `compiler_builtins` only shows up once (two static copies from multiple different locations, via [`std`, `shared`])
+   |
+   = help: having upstream crates all available in one format will likely make this go away
+
+error: cannot satisfy dependencies so `rustc_std_workspace_core` only shows up once (two static copies from multiple different locations, via [`std`, `shared`])
+   |
+   = help: having upstream crates all available in one format will likely make this go away
+
+error: cannot satisfy dependencies so `alloc` only shows up once (two static copies from multiple different locations, via [`std`, `shared`])
+   |
+   = help: having upstream crates all available in one format will likely make this go away
+
+error: cannot satisfy dependencies so `libc` only shows up once (two static copies from multiple different locations, via [`std`, `shared`])
+   |
+   = help: having upstream crates all available in one format will likely make this go away
+
+error: cannot satisfy dependencies so `unwind` only shows up once (two static copies from multiple different locations, via [`std`, `shared`])
+   |
+   = help: having upstream crates all available in one format will likely make this go away
+
+error: cannot satisfy dependencies so `cfg_if` only shows up once (two static copies from multiple different locations, via [`std`, `shared`])
+   |
+   = help: having upstream crates all available in one format will likely make this go away
+
+error: cannot satisfy dependencies so `hashbrown` only shows up once (two static copies from multiple different locations, via [`std`, `shared`])
+   |
+   = help: having upstream crates all available in one format will likely make this go away
+
+error: cannot satisfy dependencies so `rustc_std_workspace_alloc` only shows up once (two static copies from multiple different locations, via [`std`, `shared`])
+   |
+   = help: having upstream crates all available in one format will likely make this go away
+
+error: cannot satisfy dependencies so `rustc_demangle` only shows up once (two static copies from multiple different locations, via [`std`, `shared`])
+   |
+   = help: having upstream crates all available in one format will likely make this go away
+
+error: cannot satisfy dependencies so `std_detect` only shows up once (two static copies from multiple different locations, via [`std`, `shared`])
+   |
+   = help: having upstream crates all available in one format will likely make this go away
+
+error: cannot satisfy dependencies so `addr2line` only shows up once (two static copies from multiple different locations, via [`std`, `shared`])
+   |
+   = help: having upstream crates all available in one format will likely make this go away
+
+error: cannot satisfy dependencies so `gimli` only shows up once (two static copies from multiple different locations, via [`std`, `shared`])
+   |
+   = help: having upstream crates all available in one format will likely make this go away
+
+error: cannot satisfy dependencies so `object` only shows up once (two static copies from multiple different locations, via [`std`, `shared`])
+   |
+   = help: having upstream crates all available in one format will likely make this go away
+
+error: cannot satisfy dependencies so `miniz_oxide` only shows up once (two static copies from multiple different locations, via [`std`, `shared`])
+   |
+   = help: having upstream crates all available in one format will likely make this go away
+
+error: cannot satisfy dependencies so `adler` only shows up once (two static copies from multiple different locations, via [`std`, `shared`])
+   |
+   = help: having upstream crates all available in one format will likely make this go away
+
+error: cannot satisfy dependencies so `panic_unwind` only shows up once (two static copies from multiple different locations, via [`std`, `shared`])
+   |
+   = help: having upstream crates all available in one format will likely make this go away
+
+error: cannot satisfy dependencies so `bar` only shows up once (previously required static, via [`shared`], and now also requires dynamic, via [`issue_82151_serverctl_noprefdyn`])
+   |
+   = help: having upstream crates all available in one format will likely make this go away
+
+error: aborting due to 19 previous errors
+

src/test/ui/dylibs/issue-82151-serverctl-prefdyn.rs

@@ -0,0 +1,16 @@
+// build-fail
+// normalize-stderr-test "note: .*undefined reference to `bar::bar'" -> "note: undefined reference to `bar::bar'"
+// normalize-stderr-test "note: .cc..*" -> "note: $$CC_INVOCATION"
+
+// no-prefer-dynamic
+// compile-flags: -C prefer-dynamic
+
+// aux-build: aaa_issue_82151_bar_prefdyn.rs
+// aux-build: aaa_issue_82151_foo_prefdyn.rs
+// aux-build: aaa_issue_82151_shared_prefdyn.rs
+
+extern crate shared;
+
+fn main() {
+    let _ = shared::Test::new();
+}

src/test/ui/dylibs/issue-82151-serverctl-prefdyn.stderr

@@ -0,0 +1,12 @@
+error: linking with `cc` failed: exit status: 1
+   |
+   = note: $CC_INVOCATION
+   = note: undefined reference to `bar::bar'
+           collect2: error: ld returned 1 exit status
+           
+   = help: some `extern` functions couldn't be found; some native libraries may need to be installed or have their path specified
+   = note: use the `-l` flag to specify native libraries to link
+   = note: use the `cargo:rustc-link-lib` directive to specify the native libraries to link with Cargo (see https://doc.rust-lang.org/cargo/reference/build-scripts.html#cargorustc-link-libkindname)
+
+error: aborting due to previous error
+

src/test/ui/dylibs/issue-82151-serverctl-prefdynstd.rs

@@ -0,0 +1,18 @@
+// run-pass
+
+// Make use of new `-C prefer-dynamic=...` flag to allow *only* `std` to be
+// linked dynamically via the rustc injected flags, and then also manually link
+// to `shared`.
+
+// no-prefer-dynamic
+// compile-flags: -C prefer-dynamic=std -Z prefer-dynamic-std -lshared
+
+// aux-build: aaa_issue_82151_bar_prefdynstd.rs
+// aux-build: aaa_issue_82151_foo_prefdynstd.rs
+// aux-build: aaa_issue_82151_shared_prefdynstd.rs
+
+extern crate shared;
+
+fn main() {
+    let _ = shared::Test::new();
+}

src/test/ui/dylibs/issue-82151-serverctl-prefdynsubset.rs

@@ -0,0 +1,16 @@
+// run-pass
+
+// Make use of new `-C prefer-dynamic=...` to choose `shared` and `std` to be linked dynamically.
+
+// no-prefer-dynamic
+// compile-flags: -C prefer-dynamic=shared,std -Z prefer-dynamic-subset
+
+// aux-build: aaa_issue_82151_bar_prefdynsubset.rs
+// aux-build: aaa_issue_82151_foo_prefdynsubset.rs
+// aux-build: aaa_issue_82151_shared_prefdynsubset.rs
+
+extern crate shared;
+
+fn main() {
+    let _ = shared::Test::new();
+}