Auto merge of #118788 - compiler-errors:const-pretty, r=fee1-dead

Don't print host effect param in pretty `path_generic_args`

Make `own_args_no_defaults` pass back the `GenericParamDef`, so that we can pass both the args *and* param definitions into `path_generic_args`. That allows us to use the `GenericParamDef` to filter out effect params.

This allows us to filter out the host param regardless of whether it's `sym::host` or `true`/`false`.

This also renames a couple of `const_effect_param` -> `host_effect_param`, and restores `~const` pretty printing to `TraitPredPrintModifiersAndPath`.

cc #118785
r? `@fee1-dead` cc `@oli-obk`

4 files changed, 38 insertions, 41 deletions

diff --git a/compiler/rustc_middle/src/ty/generics.rs b/compiler/rustc_middle/src/ty/generics.rs
index 8316f9c3058..12294b0a602 100644
--- a/compiler/rustc_middle/src/ty/generics.rs
+++ b/compiler/rustc_middle/src/ty/generics.rs
@@ -320,9 +320,11 @@ impl<'tcx> Generics {
         &'tcx self,
         tcx: TyCtxt<'tcx>,
         args: &'tcx [ty::GenericArg<'tcx>],
-    ) -> &'tcx [ty::GenericArg<'tcx>] {
-        let mut own_params = self.parent_count..self.count();
+    ) -> (&'tcx [ty::GenericArg<'tcx>], &'tcx [ty::GenericParamDef]) {
+        let mut own_args = self.parent_count..self.count();
+        let mut own_params = 0..self.params.len();
         if self.has_self && self.parent.is_none() {
+            own_args.start = 1;
             own_params.start = 1;
         }
 
@@ -332,7 +334,7 @@ impl<'tcx> Generics {
         // of semantic equivalence. While not ideal, that's
         // good enough for now as this should only be used
         // for diagnostics anyways.
-        own_params.end -= self
+        let num_default_params = self
             .params
             .iter()
             .rev()
@@ -342,8 +344,10 @@ impl<'tcx> Generics {
                 })
             })
             .count();
+        own_params.end -= num_default_params;
+        own_args.end -= num_default_params;
 
-        &args[own_params]
+        (&args[own_args], &self.params[own_params])
     }
 
     /// Returns the args corresponding to the generic parameters of this item, excluding `Self`.
diff --git a/compiler/rustc_middle/src/ty/print/mod.rs b/compiler/rustc_middle/src/ty/print/mod.rs
index 5e09154789a..948246c64e2 100644
--- a/compiler/rustc_middle/src/ty/print/mod.rs
+++ b/compiler/rustc_middle/src/ty/print/mod.rs
@@ -83,6 +83,7 @@ pub trait Printer<'tcx>: Sized {
         &mut self,
         print_prefix: impl FnOnce(&mut Self) -> Result<(), PrintError>,
         args: &[GenericArg<'tcx>],
+        params: &[ty::GenericParamDef],
     ) -> Result<(), PrintError>;
 
     // Defaults (should not be overridden):
@@ -141,10 +142,12 @@ pub trait Printer<'tcx>: Sized {
                         // on top of the same path, but without its own generics.
                         _ => {
                             if !generics.params.is_empty() && args.len() >= generics.count() {
-                                let args = generics.own_args_no_defaults(self.tcx(), args);
+                                let (args, params) =
+                                    generics.own_args_no_defaults(self.tcx(), args);
                                 return self.path_generic_args(
                                     |cx| cx.print_def_path(def_id, parent_args),
                                     args,
+                                    params,
                                 );
                             }
                         }
diff --git a/compiler/rustc_middle/src/ty/print/pretty.rs b/compiler/rustc_middle/src/ty/print/pretty.rs
index bd9f0fd3ea9..fd53111001b 100644
--- a/compiler/rustc_middle/src/ty/print/pretty.rs
+++ b/compiler/rustc_middle/src/ty/print/pretty.rs
@@ -19,7 +19,6 @@ use rustc_hir::LangItem;
 use rustc_session::config::TrimmedDefPaths;
 use rustc_session::cstore::{ExternCrate, ExternCrateSource};
 use rustc_session::Limit;
-use rustc_span::sym;
 use rustc_span::symbol::{kw, Ident, Symbol};
 use rustc_span::FileNameDisplayPreference;
 use rustc_target::abi::Size;
@@ -967,7 +966,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
                 define_scoped_cx!(cx);
                 // Get the (single) generic ty (the args) of this FnOnce trait ref.
                 let generics = tcx.generics_of(trait_ref.def_id);
-                let own_args = generics.own_args_no_defaults(tcx, trait_ref.args);
+                let (own_args, _) = generics.own_args_no_defaults(tcx, trait_ref.args);
 
                 match (entry.return_ty, own_args[0].expect_ty()) {
                     // We can only print `impl Fn() -> ()` if we have a tuple of args and we recorded
@@ -1033,7 +1032,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
                 p!(print(trait_ref.print_only_trait_name()));
 
                 let generics = tcx.generics_of(trait_ref.def_id);
-                let own_args = generics.own_args_no_defaults(tcx, trait_ref.args);
+                let (own_args, _) = generics.own_args_no_defaults(tcx, trait_ref.args);
 
                 if !own_args.is_empty() || !assoc_items.is_empty() {
                     let mut first = true;
@@ -1185,6 +1184,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
                 )
             },
             &alias_ty.args[1..],
+            &self.tcx().generics_of(alias_ty.def_id).params,
         )
     }
 
@@ -1233,7 +1233,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
                     let dummy_cx = Ty::new_fresh(cx.tcx(), 0);
                     let principal = principal.with_self_ty(cx.tcx(), dummy_cx);
 
-                    let args = cx
+                    let (args, _) = cx
                         .tcx()
                         .generics_of(principal.def_id)
                         .own_args_no_defaults(cx.tcx(), principal.args);
@@ -2031,40 +2031,26 @@ impl<'tcx> Printer<'tcx> for FmtPrinter<'_, 'tcx> {
         &mut self,
         print_prefix: impl FnOnce(&mut Self) -> Result<(), PrintError>,
         args: &[GenericArg<'tcx>],
+        params: &[ty::GenericParamDef],
     ) -> Result<(), PrintError> {
         print_prefix(self)?;
 
         let tcx = self.tcx;
-
-        let args = args.iter().copied();
-
-        let args: Vec<_> = if !tcx.sess.verbose() {
-            // skip host param as those are printed as `~const`
-            args.filter(|arg| match arg.unpack() {
-                // FIXME(effects) there should be a better way than just matching the name
-                GenericArgKind::Const(c)
-                    if tcx.features().effects
-                        && matches!(
-                            c.kind(),
-                            ty::ConstKind::Param(ty::ParamConst { name: sym::host, .. })
-                        ) =>
-                {
-                    false
-                }
-                _ => true,
-            })
-            .collect()
-        } else {
+        let verbose = tcx.sess.verbose();
+        let mut args = args
+            .iter()
+            .copied()
+            .zip(params)
             // If -Zverbose is passed, we should print the host parameter instead
             // of eating it.
-            args.collect()
-        };
+            .filter(|(_, param)| verbose || !param.is_host_effect())
+            .peekable();
 
-        if !args.is_empty() {
+        if args.peek().is_some() {
             if self.in_value {
                 write!(self, "::")?;
             }
-            self.generic_delimiters(|cx| cx.comma_sep(args.into_iter()))
+            self.generic_delimiters(|cx| cx.comma_sep(args.map(|(arg, _)| arg)))
         } else {
             Ok(())
         }
@@ -2894,11 +2880,15 @@ define_print_and_forward_display! {
     }
 
     TraitPredPrintModifiersAndPath<'tcx> {
-        // FIXME(effects) print `~const` here
+        if let Some(idx) = cx.tcx().generics_of(self.0.trait_ref.def_id).host_effect_index
+        {
+            if self.0.trait_ref.args.const_at(idx) != cx.tcx().consts.true_ {
+                p!("~const ");
+            }
+        }
         if let ty::ImplPolarity::Negative = self.0.polarity {
             p!("!")
         }
-
         p!(print(self.0.trait_ref.print_only_trait_path()));
     }
 
@@ -2933,7 +2923,6 @@ define_print_and_forward_display! {
                 p!("~const ");
             }
         }
-        // FIXME(effects) print `~const` here
         if let ty::ImplPolarity::Negative = self.polarity {
             p!("!");
         }
diff --git a/compiler/rustc_middle/src/ty/util.rs b/compiler/rustc_middle/src/ty/util.rs
index b7c3edee9e5..1da090a7e46 100644
--- a/compiler/rustc_middle/src/ty/util.rs
+++ b/compiler/rustc_middle/src/ty/util.rs
@@ -782,7 +782,7 @@ impl<'tcx> TyCtxt<'tcx> {
             || self.extern_crate(key.as_def_id()).is_some_and(|e| e.is_direct())
     }
 
-    pub fn expected_const_effect_param_for_body(self, def_id: LocalDefId) -> ty::Const<'tcx> {
+    pub fn expected_host_effect_param_for_body(self, def_id: LocalDefId) -> ty::Const<'tcx> {
         // FIXME(effects): This is suspicious and should probably not be done,
         // especially now that we enforce host effects and then properly handle
         // effect vars during fallback.
@@ -817,7 +817,7 @@ impl<'tcx> TyCtxt<'tcx> {
     }
 
     /// Constructs generic args for an item, optionally appending a const effect param type
-    pub fn with_opt_const_effect_param(
+    pub fn with_opt_host_effect_param(
         self,
         caller_def_id: LocalDefId,
         callee_def_id: DefId,
@@ -826,9 +826,10 @@ impl<'tcx> TyCtxt<'tcx> {
         let generics = self.generics_of(callee_def_id);
         assert_eq!(generics.parent, None);
 
-        let opt_const_param = generics.host_effect_index.is_some().then(|| {
-            ty::GenericArg::from(self.expected_const_effect_param_for_body(caller_def_id))
-        });
+        let opt_const_param = generics
+            .host_effect_index
+            .is_some()
+            .then(|| ty::GenericArg::from(self.expected_host_effect_param_for_body(caller_def_id)));
 
         self.mk_args_from_iter(args.into_iter().map(|arg| arg.into()).chain(opt_const_param))
     }