2 files changed, 61 insertions, 12 deletions

diff --git a/compiler/rustc_lint_defs/src/builtin.rs b/compiler/rustc_lint_defs/src/builtin.rs
index 46ec1a2dc..9d6ab0b75 100644
--- a/compiler/rustc_lint_defs/src/builtin.rs
+++ b/compiler/rustc_lint_defs/src/builtin.rs
@@ -1026,12 +1026,13 @@ declare_lint! {
     /// ### Example
     ///
     /// ```rust,compile_fail
-    /// #![feature(const_ptr_read)]
+    /// #![feature(const_mut_refs)]
     /// const FOO: () = unsafe {
     ///     let x = &[0_u8; 4];
     ///     let y = x.as_ptr().cast::<u32>();
-    ///     y.read(); // the address of a `u8` array is unknown and thus we don't know if
-    ///     // it is aligned enough for reading a `u32`.
+    ///     let mut z = 123;
+    ///     y.copy_to_nonoverlapping(&mut z, 1); // the address of a `u8` array is unknown
+    ///     // and thus we don't know if it is aligned enough for copying a `u32`.
     /// };
     /// ```
     ///
@@ -3229,6 +3230,45 @@ declare_lint! {
     };
 }
 
+declare_lint! {
+    /// The `ambiguous_glob_reexports` lint detects cases where names re-exported via globs
+    /// collide. Downstream users trying to use the same name re-exported from multiple globs
+    /// will receive a warning pointing out redefinition of the same name.
+    ///
+    /// ### Example
+    ///
+    /// ```rust,compile_fail
+    /// #![deny(ambiguous_glob_reexports)]
+    /// pub mod foo {
+    ///     pub type X = u8;
+    /// }
+    ///
+    /// pub mod bar {
+    ///     pub type Y = u8;
+    ///     pub type X = u8;
+    /// }
+    ///
+    /// pub use foo::*;
+    /// pub use bar::*;
+    ///
+    ///
+    /// pub fn main() {}
+    /// ```
+    ///
+    /// {{produces}}
+    ///
+    /// ### Explanation
+    ///
+    /// This was previously accepted but it could silently break a crate's downstream users code.
+    /// For example, if `foo::*` and `bar::*` were re-exported before `bar::X` was added to the
+    /// re-exports, down stream users could use `this_crate::X` without problems. However, adding
+    /// `bar::X` would cause compilation errors in downstream crates because `X` is defined
+    /// multiple times in the same namespace of `this_crate`.
+    pub AMBIGUOUS_GLOB_REEXPORTS,
+    Warn,
+    "ambiguous glob re-exports",
+}
+
 declare_lint_pass! {
     /// Does nothing as a lint pass, but registers some `Lint`s
     /// that are used by other parts of the compiler.
@@ -3336,6 +3376,7 @@ declare_lint_pass! {
         NAMED_ARGUMENTS_USED_POSITIONALLY,
         IMPLIED_BOUNDS_ENTAILMENT,
         BYTE_SLICE_IN_PACKED_STRUCT_WITH_DERIVE,
+        AMBIGUOUS_GLOB_REEXPORTS,
     ]
 }
 
@@ -3967,14 +4008,9 @@ declare_lint! {
     ///
     /// ### Example
     ///
-    /// ```rust,ignore (need FFI)
-    /// #![feature(ffi_unwind_calls)]
+    /// ```rust
     /// #![feature(c_unwind)]
-    ///
-    /// # mod impl {
-    /// #     #[no_mangle]
-    /// #     pub fn "C-unwind" fn foo() {}
-    /// # }
+    /// #![warn(ffi_unwind_calls)]
     ///
     /// extern "C-unwind" {
     ///     fn foo();
diff --git a/compiler/rustc_lint_defs/src/lib.rs b/compiler/rustc_lint_defs/src/lib.rs
index 534aff7fb..7ea472ed5 100644
--- a/compiler/rustc_lint_defs/src/lib.rs
+++ b/compiler/rustc_lint_defs/src/lib.rs
@@ -8,7 +8,7 @@ extern crate rustc_macros;
 pub use self::Level::*;
 use rustc_ast::node_id::NodeId;
 use rustc_ast::{AttrId, Attribute};
-use rustc_data_structures::fx::FxIndexMap;
+use rustc_data_structures::fx::{FxIndexMap, FxIndexSet};
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher, ToStableHashKey};
 use rustc_error_messages::{DiagnosticMessage, MultiSpan};
 use rustc_hir::HashStableContext;
@@ -529,10 +529,21 @@ pub enum BuiltinLintDiagnostics {
         vis_span: Span,
         ident_span: Span,
     },
+    AmbiguousGlobReexports {
+        /// The name for which collision(s) have occurred.
+        name: String,
+        /// The name space for which the collision(s) occurred in.
+        namespace: String,
+        /// Span where the name is first re-exported.
+        first_reexport_span: Span,
+        /// Span where the same name is also re-exported.
+        duplicate_reexport_span: Span,
+    },
 }
 
 /// Lints that are buffered up early on in the `Session` before the
 /// `LintLevels` is calculated.
+#[derive(Debug)]
 pub struct BufferedEarlyLint {
     /// The span of code that we are linting on.
     pub span: MultiSpan,
@@ -551,7 +562,7 @@ pub struct BufferedEarlyLint {
     pub diagnostic: BuiltinLintDiagnostics,
 }
 
-#[derive(Default)]
+#[derive(Default, Debug)]
 pub struct LintBuffer {
     pub map: FxIndexMap<NodeId, Vec<BufferedEarlyLint>>,
 }
@@ -601,6 +612,8 @@ impl LintBuffer {
     }
 }
 
+pub type RegisteredTools = FxIndexSet<Ident>;
+
 /// Declares a static item of type `&'static Lint`.
 ///
 /// See <https://rustc-dev-guide.rust-lang.org/diagnostics.html> for