mangling: encode all impl parameters

This commit modifies v0 symbol mangling to include all generic
parameters from impl blocks (not just those used in the self type).

Signed-off-by: David Wood <david@davidtw.co>

src/test/ui/symbol-names/issue-75326.legacy.stderr

@@ -0,0 +1,20 @@
+error: symbol-name(_ZN72_$LT$issue_75326..Foo$LT$I$C$E$GT$$u20$as$u20$issue_75326..Iterator2$GT$4next17SYMBOL_HASH)
+  --> $DIR/issue-75326.rs:43:5
+   |
+LL |     #[rustc_symbol_name]
+   |     ^^^^^^^^^^^^^^^^^^^^
+
+error: demangling(<issue_75326::Foo<I,E> as issue_75326::Iterator2>::next::SYMBOL_HASH)
+  --> $DIR/issue-75326.rs:43:5
+   |
+LL |     #[rustc_symbol_name]
+   |     ^^^^^^^^^^^^^^^^^^^^
+
+error: demangling-alt(<issue_75326::Foo<I,E> as issue_75326::Iterator2>::next)
+  --> $DIR/issue-75326.rs:43:5
+   |
+LL |     #[rustc_symbol_name]
+   |     ^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 3 previous errors
+

src/test/ui/symbol-names/issue-75326.rs

@@ -0,0 +1,58 @@
+// build-fail
+// ignore-tidy-linelength
+// revisions: legacy v0
+//[legacy]compile-flags: -Z symbol-mangling-version=legacy
+//[v0]compile-flags: -Z symbol-mangling-version=v0
+//[legacy]normalize-stderr-32bit: "h[\d\w]+" -> "SYMBOL_HASH"
+//[legacy]normalize-stderr-64bit: "h[\d\w]+" -> "SYMBOL_HASH"
+
+#![feature(rustc_attrs)]
+
+pub(crate) struct Foo<I, E>(I, E);
+
+pub trait Iterator2 {
+    type Item;
+
+    fn next(&mut self) -> Option<Self::Item>;
+
+    fn find<P>(&mut self, predicate: P) -> Option<Self::Item>
+    where
+        Self: Sized,
+        P: FnMut(&Self::Item) -> bool,
+    {
+        unimplemented!()
+    }
+}
+
+struct Bar;
+
+impl Iterator2 for Bar {
+    type Item = (u32, u16);
+
+    fn next(&mut self) -> Option<Self::Item> {
+        unimplemented!()
+    }
+}
+
+impl<I, T, E> Iterator2 for Foo<I, E>
+where
+    I: Iterator2<Item = (T, E)>,
+{
+    type Item = T;
+
+    #[rustc_symbol_name]
+    //[legacy]~^ ERROR symbol-name(_ZN72_$LT$issue_75326..Foo$LT$I$C$E$GT$$u20$as$u20$issue_75326..Iterator2$GT$4next
+    //[legacy]~| ERROR demangling(<issue_75326::Foo<I,E> as issue_75326::Iterator2>::next
+    //[legacy]~| ERROR demangling-alt(<issue_75326::Foo<I,E> as issue_75326::Iterator2>::next)
+    //[v0]~^^^^  ERROR symbol-name(_RNvXINICs4fqI2P2rA04_11issue_75326s_0pppEINtB5_3FooppENtB5_9Iterator24nextB5_)
+    //[v0]~|     ERROR demangling(<issue_75326[317d481089b8c8fe]::Foo<_, _> as issue_75326[317d481089b8c8fe]::Iterator2>::next)
+    //[v0]~|     ERROR demangling-alt(<issue_75326::Foo<_, _> as issue_75326::Iterator2>::next)
+    fn next(&mut self) -> Option<Self::Item> {
+        self.find(|_| true)
+    }
+}
+
+fn main() {
+    let mut a = Foo(Bar, 1u16);
+    let _ = a.next();
+}

src/test/ui/symbol-names/issue-75326.v0.stderr

@@ -0,0 +1,20 @@
+error: symbol-name(_RNvXINICs4fqI2P2rA04_11issue_75326s_0pppEINtB5_3FooppENtB5_9Iterator24nextB5_)
+  --> $DIR/issue-75326.rs:43:5
+   |
+LL |     #[rustc_symbol_name]
+   |     ^^^^^^^^^^^^^^^^^^^^
+
+error: demangling(<issue_75326[317d481089b8c8fe]::Foo<_, _> as issue_75326[317d481089b8c8fe]::Iterator2>::next)
+  --> $DIR/issue-75326.rs:43:5
+   |
+LL |     #[rustc_symbol_name]
+   |     ^^^^^^^^^^^^^^^^^^^^
+
+error: demangling-alt(<issue_75326::Foo<_, _> as issue_75326::Iterator2>::next)
+  --> $DIR/issue-75326.rs:43:5
+   |
+LL |     #[rustc_symbol_name]
+   |     ^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 3 previous errors
+