error on empty export_name

compiler/rustc_attr_parsing/src/attributes/codegen_attrs.rs

@@ -5,8 +5,8 @@
 use super::prelude::*;
 use crate::attributes::AttributeSafety;
 use crate::session_diagnostics::{
-    NakedFunctionIncompatibleAttribute, NullOnExport, NullOnObjcClass, NullOnObjcSelector,
-    ObjcClassExpectedStringLiteral, ObjcSelectorExpectedStringLiteral,
+    EmptyExportName, NakedFunctionIncompatibleAttribute, NullOnExport, NullOnObjcClass,
+    NullOnObjcSelector, ObjcClassExpectedStringLiteral, ObjcSelectorExpectedStringLiteral,
 };
 use crate::target_checking::Policy::AllowSilent;
 
@@ -133,6 +133,12 @@ fn convert(cx: &mut AcceptContext<'_, '_, S>, args: &ArgParser) -> Option<Attrib
             cx.emit_err(NullOnExport { span: cx.attr_span });
             return None;
         }
+        if name.is_empty() {
+            // LLVM will make up a name if the empty string is given, but that name will be
+            // inconsistent between compilation units, causing linker errors.
+            cx.emit_err(EmptyExportName { span: cx.attr_span });
+            return None;
+        }
         Some(AttributeKind::ExportName { name, span: cx.attr_span })
     }
 }

compiler/rustc_attr_parsing/src/session_diagnostics.rs

@@ -396,6 +396,13 @@ pub(crate) struct UnusedMultiple {
     pub name: Symbol,
 }
 
+#[derive(Diagnostic)]
+#[diag("`export_name` may not be empty")]
+pub(crate) struct EmptyExportName {
+    #[primary_span]
+    pub span: Span,
+}
+
 #[derive(Diagnostic)]
 #[diag("`export_name` may not contain null characters", code = E0648)]
 pub(crate) struct NullOnExport {

tests/ui/attributes/invalid-export-name.rs

@@ -0,0 +1,22 @@
+#![crate_type = "lib"]
+
+#[export_name = "\0foo"]
+//~^ ERROR `export_name` may not contain null characters
+fn has_null_byte() {}
+
+#[export_name = "foo\0"]
+//~^ ERROR `export_name` may not contain null characters
+fn null_terminated() {}
+
+#[export_name = "\0"]
+//~^ ERROR `export_name` may not contain null characters
+fn empty_null() {}
+
+#[export_name = ""]
+//~^ ERROR `export_name` may not be empty
+fn empty() {}
+
+#[export_name = "\
+"]
+//~^^ ERROR `export_name` may not be empty
+fn empty_newline() {}

tests/ui/attributes/invalid-export-name.stderr

@@ -0,0 +1,34 @@
+error[E0648]: `export_name` may not contain null characters
+  --> $DIR/invalid-export-name.rs:3:1
+   |
+LL | #[export_name = "\0foo"]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0648]: `export_name` may not contain null characters
+  --> $DIR/invalid-export-name.rs:7:1
+   |
+LL | #[export_name = "foo\0"]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0648]: `export_name` may not contain null characters
+  --> $DIR/invalid-export-name.rs:11:1
+   |
+LL | #[export_name = "\0"]
+   | ^^^^^^^^^^^^^^^^^^^^^
+
+error: `export_name` may not be empty
+  --> $DIR/invalid-export-name.rs:15:1
+   |
+LL | #[export_name = ""]
+   | ^^^^^^^^^^^^^^^^^^^
+
+error: `export_name` may not be empty
+  --> $DIR/invalid-export-name.rs:19:1
+   |
+LL | / #[export_name = "\
+LL | | "]
+   | |__^
+
+error: aborting due to 5 previous errors
+
+For more information about this error, try `rustc --explain E0648`.