librustc: Forbid external crates, imports, and/or items from being

declared with the same name in the same scope.

This breaks several common patterns. First are unused imports:

    use foo::bar;
    use baz::bar;

Change this code to the following:

    use baz::bar;

Second, this patch breaks globs that import names that are shadowed by
subsequent imports. For example:

    use foo::*; // including `bar`
    use baz::bar;

Change this code to remove the glob:

    use foo::{boo, quux};
    use baz::bar;

Or qualify all uses of `bar`:

    use foo::{boo, quux};
    use baz;

    ... baz::bar ...

Finally, this patch breaks code that, at top level, explicitly imports
`std` and doesn't disable the prelude.

    extern crate std;

Because the prelude imports `std` implicitly, there is no need to
explicitly import it; just remove such directives.

The old behavior can be opted into via the `import_shadowing` feature
gate. Use of this feature gate is discouraged.

This implements RFC #116.

Closes #16464.

[breaking-change]

1 files changed, 3 insertions, 3 deletions

diff --git a/src/liblibc/lib.rs b/src/liblibc/lib.rs
index c005ae71480..bf0a9f06df8 100644
--- a/src/liblibc/lib.rs
+++ b/src/liblibc/lib.rs
@@ -226,7 +226,7 @@ pub use funcs::bsd43::{shutdown};
 #[cfg(windows)] pub use consts::os::extra::{FILE_FLAG_BACKUP_SEMANTICS, INVALID_HANDLE_VALUE};
 #[cfg(windows)] pub use consts::os::extra::{MOVEFILE_REPLACE_EXISTING};
 #[cfg(windows)] pub use consts::os::extra::{GENERIC_READ, GENERIC_WRITE};
-#[cfg(windows)] pub use consts::os::extra::{VOLUME_NAME_DOS, FILE_ATTRIBUTE_NORMAL};
+#[cfg(windows)] pub use consts::os::extra::{VOLUME_NAME_DOS};
 #[cfg(windows)] pub use consts::os::extra::{PIPE_ACCESS_DUPLEX, FILE_FLAG_FIRST_PIPE_INSTANCE};
 #[cfg(windows)] pub use consts::os::extra::{FILE_FLAG_OVERLAPPED, PIPE_TYPE_BYTE};
 #[cfg(windows)] pub use consts::os::extra::{PIPE_READMODE_BYTE, PIPE_WAIT};
@@ -255,10 +255,10 @@ pub use funcs::bsd43::{shutdown};
 #[cfg(windows)] pub use funcs::extra::kernel32::{UnmapViewOfFile, CloseHandle};
 #[cfg(windows)] pub use funcs::extra::kernel32::{WaitForSingleObject, GetSystemTimeAsFileTime};
 #[cfg(windows)] pub use funcs::extra::kernel32::{QueryPerformanceCounter};
-#[cfg(windows)] pub use funcs::extra::kernel32::{WaitForSingleObject, QueryPerformanceFrequency};
+#[cfg(windows)] pub use funcs::extra::kernel32::{QueryPerformanceFrequency};
 #[cfg(windows)] pub use funcs::extra::kernel32::{GetExitCodeProcess, TerminateProcess};
 #[cfg(windows)] pub use funcs::extra::kernel32::{ReadFile, WriteFile, SetFilePointerEx};
-#[cfg(windows)] pub use funcs::extra::kernel32::{FlushFileBuffers, SetEndOfFile, CreateFileW};
+#[cfg(windows)] pub use funcs::extra::kernel32::{SetEndOfFile, CreateFileW};
 #[cfg(windows)] pub use funcs::extra::kernel32::{CreateDirectoryW, FindFirstFileW};
 #[cfg(windows)] pub use funcs::extra::kernel32::{FindNextFileW, FindClose, DeleteFileW};
 #[cfg(windows)] pub use funcs::extra::kernel32::{CreateHardLinkW, CreateEventW};