rustdoc: properly elide cross-crate host effect args

src/librustdoc/clean/mod.rs

@@ -2534,7 +2534,8 @@ fn clean_generic_args<'tcx>(
                     }
                     hir::GenericArg::Lifetime(_) => GenericArg::Lifetime(Lifetime::elided()),
                     hir::GenericArg::Type(ty) => GenericArg::Type(clean_ty(ty, cx)),
-                    // FIXME(effects): This will still emit `<true>` for non-const impls of const traits
+                    // Checking for `#[rustc_host]` on the `AnonConst`  not only accounts for the case
+                    // where the argument is `host` but for all possible cases (e.g., `true`, `false`).
                     hir::GenericArg::Const(ct)
                         if cx.tcx.has_attr(ct.value.def_id, sym::rustc_host) =>
                     {

src/librustdoc/clean/utils.rs

@@ -124,11 +124,7 @@ pub(crate) fn ty_args_to_args<'tcx>(
             )))
         }
         GenericArgKind::Const(ct) => {
-            // FIXME(effects): this relies on the host effect being called `host`, which users could also name
-            // their const generics.
-            // FIXME(effects): this causes `host = true` and `host = false` generics to also be emitted.
-            if let ty::ConstKind::Param(p) = ct.kind()
-                && p.name == sym::host
+            if let ty::GenericParamDefKind::Const { is_host_effect: true, .. } = params[index].kind
             {
                 return None;
             }

tests/rustdoc/const-effect-param.rs

@@ -1,3 +1,5 @@
+// Check that we don't render host effect parameters & arguments.
+
 #![crate_name = "foo"]
 #![feature(effects, const_trait_impl)]
 

tests/rustdoc/inline_cross/auxiliary/const-effect-param.rs

@@ -0,0 +1,18 @@
+#![feature(effects, const_trait_impl)]
+
+#[const_trait]
+pub trait Resource {}
+
+impl Resource for () {}
+
+pub const fn load<R: ~const Resource>() -> i32 {
+    0
+}
+
+pub const fn lock<R: Resource>() {}
+
+#[allow(non_upper_case_globals)]
+pub trait Clash<const host: u64> {}
+
+#[allow(non_upper_case_globals)]
+pub const fn clash<T: Clash<host>, const host: u64>() {}

tests/rustdoc/inline_cross/auxiliary/u_const_effect_param.rs

@@ -0,0 +1 @@
+pub use const_effect_param::*;

tests/rustdoc/inline_cross/const-effect-param.rs

@@ -0,0 +1,29 @@
+// Regression test for issue #116629.
+// Check that we don't render host effect parameters & arguments.
+
+// aux-crate:const_effect_param=const-effect-param.rs
+// edition: 2021
+#![crate_name = "user"]
+
+// Don't render the host param on `load` and the host arg `host` passed to `Resource`.
+// @has user/fn.load.html
+// @has - '//pre[@class="rust item-decl"]' "pub const fn load<R>() -> i32\
+//     where \
+//         R: Resource"
+pub use const_effect_param::load;
+
+// Don't render the host arg `true` passed to `Resource`.
+// @has user/fn.lock.html
+// @has - '//pre[@class="rust item-decl"]' "pub const fn lock<R>()\
+//     where \
+//         R: Resource"
+pub use const_effect_param::lock;
+
+// Regression test for an issue introduced in PR #116670.
+// Don't hide the const param `host` since it actually isn't the host effect param.
+// @has user/fn.clash.html
+// @has - '//pre[@class="rust item-decl"]' \
+//    "pub const fn clash<T, const host: u64>()\
+//     where \
+//         T: Clash<host>"
+pub use const_effect_param::clash;