Filter elided lifetimes in HIR pretty printing

Author: Urgau

compiler/rustc_ast_pretty/src/pprust/state.rs

@@ -424,20 +424,23 @@ pub trait PrintState<'a>: std::ops::Deref<Target = pp::Printer> + std::ops::Dere
         self.ann_post(ident)
     }
 
-    fn strsep<T, F>(
+    fn strsep<'x, T: 'x, F, I>(
         &mut self,
         sep: &'static str,
         space_before: bool,
         b: Breaks,
-        elts: &[T],
+        elts: I,
         mut op: F,
     ) where
         F: FnMut(&mut Self, &T),
+        I: IntoIterator<Item = &'x T>,
     {
+        let mut it = elts.into_iter();
+
         self.rbox(0, b);
-        if let Some((first, rest)) = elts.split_first() {
+        if let Some(first) = it.next() {
             op(self, first);
-            for elt in rest {
+            for elt in it {
                 if space_before {
                     self.space();
                 }
@@ -448,9 +451,10 @@ pub trait PrintState<'a>: std::ops::Deref<Target = pp::Printer> + std::ops::Dere
         self.end();
     }
 
-    fn commasep<T, F>(&mut self, b: Breaks, elts: &[T], op: F)
+    fn commasep<'x, T: 'x, F, I>(&mut self, b: Breaks, elts: I, op: F)
     where
         F: FnMut(&mut Self, &T),
+        I: IntoIterator<Item = &'x T>,
     {
         self.strsep(",", false, b, elts, op)
     }

compiler/rustc_hir_pretty/src/lib.rs

@@ -2284,7 +2284,9 @@ impl<'a> State<'a> {
                 GenericBound::Use(args, _) => {
                     self.word("use <");
 
-                    self.commasep(Inconsistent, args, |s, arg| s.print_precise_capturing_arg(*arg));
+                    self.commasep(Inconsistent, *args, |s, arg| {
+                        s.print_precise_capturing_arg(*arg)
+                    });
 
                     self.word(">");
                 }
@@ -2300,10 +2302,23 @@ impl<'a> State<'a> {
     }
 
     fn print_generic_params(&mut self, generic_params: &[GenericParam<'_>]) {
-        if !generic_params.is_empty() {
+        let is_lifetime_elided = |generic_param: &GenericParam<'_>| {
+            matches!(
+                generic_param.kind,
+                GenericParamKind::Lifetime { kind: LifetimeParamKind::Elided(_) }
+            )
+        };
+
+        // We don't want to show elided lifetimes as they are compiler-inserted and not
+        // expressible in surface level Rust.
+        if !generic_params.is_empty() && !generic_params.iter().all(is_lifetime_elided) {
             self.word("<");
 
-            self.commasep(Inconsistent, generic_params, |s, param| s.print_generic_param(param));
+            self.commasep(
+                Inconsistent,
+                generic_params.iter().filter(|gp| !is_lifetime_elided(gp)),
+                |s, param| s.print_generic_param(param),
+            );
 
             self.word(">");
         }

tests/ui/unpretty/debug-fmt-hir.stdout

@@ -13,13 +13,13 @@ struct Bar {
 }
 
 impl fmt::Debug for Bar {
-    fn fmt<'_, '_, '_>(self: &'_ Self, f: &'_ mut fmt::Formatter<'_>)
+    fn fmt(self: &'_ Self, f: &'_ mut fmt::Formatter<'_>)
         ->
             fmt::Result {
         debug_struct_field2_finish(f, "Bar", "a", &self.a, "b", &&self.b)
     }
 }
 
-fn debug_struct_field2_finish<'a, '_, '_,
-    '_>(name: &'_ str, name1: &'_ str, value1: &'a dyn fmt::Debug,
-    name2: &'_ str, value2: &'a dyn fmt::Debug) -> fmt::Result { loop { } }
+fn debug_struct_field2_finish<'a>(name: &'_ str, name1: &'_ str,
+    value1: &'a dyn fmt::Debug, name2: &'_ str, value2: &'a dyn fmt::Debug)
+    -> fmt::Result { loop { } }