Future compatibility warning on cfg_attr on crate_type and crate_name

compiler/rustc_expand/src/config.rs

@@ -402,7 +402,24 @@ fn process_cfg_attr(&mut self, attr: Attribute) -> Vec<Attribute> {
                 );
                 trees.push((bracket_group, Spacing::Alone));
                 let tokens = Some(LazyTokenStream::new(AttrAnnotatedTokenStream::new(trees)));
-                self.process_cfg_attr(attr::mk_attr_from_item(item, tokens, attr.style, span))
+                let attr = attr::mk_attr_from_item(item, tokens, attr.style, span);
+                if attr.has_name(sym::crate_type) {
+                    self.sess.parse_sess.buffer_lint(
+                        rustc_lint_defs::builtin::DEPRECATED_CFG_ATTR_CRATE_TYPE_NAME,
+                        attr.span,
+                        ast::CRATE_NODE_ID,
+                        "`crate_type` within an `#![cfg_attr] attribute is deprecated`",
+                    );
+                }
+                if attr.has_name(sym::crate_name) {
+                    self.sess.parse_sess.buffer_lint(
+                        rustc_lint_defs::builtin::DEPRECATED_CFG_ATTR_CRATE_TYPE_NAME,
+                        attr.span,
+                        ast::CRATE_NODE_ID,
+                        "`crate_name` within an `#![cfg_attr] attribute is deprecated`",
+                    );
+                }
+                self.process_cfg_attr(attr)
             })
             .collect()
     }

compiler/rustc_lint_defs/src/builtin.rs

@@ -2960,6 +2960,41 @@
     "detects large moves or copies",
 }
 
+declare_lint! {
+    /// The `deprecated_cfg_attr_crate_type_name` lint detects uses of the
+    /// `#![cfg_attr(..., crate_type = "...")]` and
+    /// `#![cfg_attr(..., crate_name = "...")]` attributes to conditionally
+    /// specify the crate type and name in the source code.
+    ///
+    /// ### Example
+    ///
+    /// ```rust
+    /// #![cfg_attr(debug_assertions, crate_type = "lib")]
+    /// ```
+    ///
+    /// {{produces}}
+    ///
+    ///
+    /// ### Explanation
+    ///
+    /// The `#![crate_type]` and `#![crate_name]` attributes require a hack in
+    /// the compiler to be able to change the used crate type and crate name
+    /// after macros have been expanded. Neither attribute works in combination
+    /// with Cargo as it explicitly passes `--crate-type` and `--crate-name` on
+    /// the commandline. These values must match the value used in the source
+    /// code to prevent an error.
+    ///
+    /// To fix the warning use `--crate-type` on the commandline when running
+    /// rustc instead of `#![cfg_attr(..., crate_type = "...")]` and
+    /// `--crate-name` instead of `#![cfg_attr(..., crate_name = "...")]`.
+    pub DEPRECATED_CFG_ATTR_CRATE_TYPE_NAME,
+    Warn,
+    "detects usage of `#![cfg_attr(..., crate_type/crate_name = \"...\")]`",
+    @future_incompatible = FutureIncompatibleInfo {
+        reference: "issue #91632 <https://github.com/rust-lang/rust/issues/91632>",
+    };
+}
+
 declare_lint_pass! {
     /// Does nothing as a lint pass, but registers some `Lint`s
     /// that are used by other parts of the compiler.
@@ -3056,6 +3091,7 @@
         NON_EXHAUSTIVE_OMITTED_PATTERNS,
         TEXT_DIRECTION_CODEPOINT_IN_COMMENT,
         DEREF_INTO_DYN_SUPERTRAIT,
+        DEPRECATED_CFG_ATTR_CRATE_TYPE_NAME,
     ]
 }
 

src/test/ui/cfg/auxiliary/crate-attributes-using-cfg_attr.rs

@@ -1,6 +0,0 @@
-// no-prefer-dynamic
-// compile-flags: --cfg foo
-
-#![cfg_attr(foo, crate_type="lib")]
-
-pub fn foo() {}

src/test/ui/cfg/crate-attributes-using-cfg_attr.rs

@@ -1,6 +0,0 @@
-// run-pass
-// aux-build:crate-attributes-using-cfg_attr.rs
-
-extern crate crate_attributes_using_cfg_attr;
-
-pub fn main() {}

src/test/ui/cfg/future-compat-crate-attributes-using-cfg_attr.rs

@@ -0,0 +1,12 @@
+// check-fail
+// compile-flags:--cfg foo
+
+#![deny(warnings)]
+#![cfg_attr(foo, crate_type="bin")]
+//~^ERROR `crate_type` within
+//~| WARN this was previously accepted
+#![cfg_attr(foo, crate_name="bar")]
+//~^ERROR `crate_name` within
+//~| WARN this was previously accepted
+
+fn main() {}

src/test/ui/cfg/future-compat-crate-attributes-using-cfg_attr.stderr

@@ -0,0 +1,26 @@
+error: `crate_type` within an `#![cfg_attr] attribute is deprecated`
+  --> $DIR/future-compat-crate-attributes-using-cfg_attr.rs:5:18
+   |
+LL | #![cfg_attr(foo, crate_type="bin")]
+   |                  ^^^^^^^^^^^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/future-compat-crate-attributes-using-cfg_attr.rs:4:9
+   |
+LL | #![deny(warnings)]
+   |         ^^^^^^^^
+   = note: `#[deny(deprecated_cfg_attr_crate_type_name)]` implied by `#[deny(warnings)]`
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #91632 <https://github.com/rust-lang/rust/issues/91632>
+
+error: `crate_name` within an `#![cfg_attr] attribute is deprecated`
+  --> $DIR/future-compat-crate-attributes-using-cfg_attr.rs:8:18
+   |
+LL | #![cfg_attr(foo, crate_name="bar")]
+   |                  ^^^^^^^^^^^^^^^^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #91632 <https://github.com/rust-lang/rust/issues/91632>
+
+error: aborting due to 2 previous errors
+