tests: Check error when struct from wrong crate version is used for impl

Author: Enselic

tests/run-make/duplicate-dependency/foo-v1.rs

@@ -0,0 +1 @@
+pub struct Foo;

tests/run-make/duplicate-dependency/foo-v2.rs

@@ -0,0 +1 @@
+pub struct Foo;

tests/run-make/duplicate-dependency/main.rs

@@ -0,0 +1,15 @@
+struct Bar;
+
+impl From<Bar> for foo::Foo {
+    fn from(_: Bar) -> Self {
+        foo::Foo
+    }
+}
+
+fn main() {
+    // The user might wrongly expect this to work since From<Bar> for Foo
+    // implies Into<Foo> for Bar. What the user missed is that different
+    // versions of Foo exist in the dependency graph, and the impl is for the
+    // wrong version.
+    re_export_foo::into_foo(Bar);
+}

tests/run-make/duplicate-dependency/main.stderr

@@ -0,0 +1,18 @@
+error[E0277]: the trait bound `re_export_foo::foo::Foo: From<Bar>` is not satisfied
+  --> main.rs:14:29
+   |
+LL |     re_export_foo::into_foo(Bar);
+   |     ----------------------- ^^^ the trait `From<Bar>` is not implemented for `re_export_foo::foo::Foo`
+   |     |
+   |     required by a bound introduced by this call
+   |
+   = note: required for `Bar` to implement `Into<re_export_foo::foo::Foo>`
+note: required by a bound in `into_foo`
+  --> $DIR/re-export-foo.rs:3:25
+   |
+LL | pub fn into_foo(_: impl Into<foo::Foo>) {}
+   |                         ^^^^^^^^^^^^^^ required by this bound in `into_foo`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0277`.

tests/run-make/duplicate-dependency/re-export-foo.rs

@@ -0,0 +1,3 @@
+pub use foo;
+
+pub fn into_foo(_: impl Into<foo::Foo>) {}

tests/run-make/duplicate-dependency/rmake.rs

@@ -0,0 +1,43 @@
+use run_make_support::{Rustc, cwd, diff, rust_lib_name, rustc};
+
+fn rustc_with_common_args() -> Rustc {
+    let mut rustc = rustc();
+    rustc.remap_path_prefix(cwd(), "$DIR");
+    rustc.edition("2018"); // Don't require `extern crate`
+    rustc
+}
+
+fn main() {
+    rustc_with_common_args()
+        .input("foo-v1.rs")
+        .crate_type("rlib")
+        .crate_name("foo")
+        .extra_filename("-v1")
+        .metadata("-v1")
+        .run();
+
+    rustc_with_common_args()
+        .input("foo-v2.rs")
+        .crate_type("rlib")
+        .crate_name("foo")
+        .extra_filename("-v2")
+        .metadata("-v2")
+        .run();
+
+    rustc_with_common_args()
+        .input("re-export-foo.rs")
+        .crate_type("rlib")
+        .extern_("foo", rust_lib_name("foo-v2"))
+        .run();
+
+    let stderr = rustc_with_common_args()
+        .input("main.rs")
+        .extern_("foo", rust_lib_name("foo-v1"))
+        .extern_("re_export_foo", rust_lib_name("re_export_foo"))
+        .library_search_path(cwd())
+        .ui_testing()
+        .run_fail()
+        .stderr_utf8();
+
+    diff().expected_file("main.stderr").actual_text("(rustc)", &stderr).run();
+}