also skip abi_required_features check in rustdoc

Author: RalfJung

compiler/rustc_codegen_ssa/src/target_features.rs

@@ -87,12 +87,17 @@ pub(crate) fn from_target_feature_attr(
                     // But ensure the ABI does not forbid enabling this.
                     // Here we do assume that LLVM doesn't add even more implied features
                     // we don't know about, at least no features that would have ABI effects!
-                    if abi_feature_constraints.incompatible.contains(&name.as_str()) {
-                        tcx.dcx().emit_err(errors::ForbiddenTargetFeatureAttr {
-                            span: item.span(),
-                            feature: name.as_str(),
-                            reason: "this feature is incompatible with the target ABI",
-                        });
+                    // We skip this logic in rustdoc, where we want to allow all target features of
+                    // all targets, so we can't check their ABI compatibility and anyway we are not
+                    // generating code so "it's fine".
+                    if tcx.sess.opts.actually_rustdoc {
+                        if abi_feature_constraints.incompatible.contains(&name.as_str()) {
+                            tcx.dcx().emit_err(errors::ForbiddenTargetFeatureAttr {
+                                span: item.span(),
+                                feature: name.as_str(),
+                                reason: "this feature is incompatible with the target ABI",
+                            });
+                        }
                     }
                     target_features.push(TargetFeature { name, implied: name != feature_sym })
                 }

tests/rustdoc-ui/target-feature-stability.rs

@@ -3,7 +3,9 @@
 //! being a "forbidden" feature of the same name for aarch64, and rustdoc merging the
 //! target features of all targets.
 //@ check-pass
-//@ compile-flags: --target armv7-unknown-linux-gnueabihf
+//@ revisions: arm aarch64
+//@[arm] compile-flags: --target armv7-unknown-linux-gnueabihf
+//@[aarch64] compile-flags: --target aarch64-unknown-none-softfloat
 
 #![crate_type = "lib"]
 #![feature(no_core, lang_items)]
@@ -15,4 +17,9 @@ pub trait Sized {}
 
 // `fp-armv8` is "forbidden" on aarch64 as we tie it to `neon`.
 #[target_feature(enable = "fp-armv8")]
-pub fn fun() {}
+pub fn fun1() {}
+
+// This would usually be rejected on aarch64-softfloat as it changes the ABI.
+// But it can legimiately occur on ARMv7 so we have to accept it in rustdoc on all targets.
+#[target_feature(enable = "neon")]
+pub fn fun2() {}