Add incremental tests.

tests/incremental/const-generics/change-const-param-gat.rs

@@ -0,0 +1,29 @@
+// revisions: rpass1 rpass2 rpass3
+// compile-flags: -Zincremental-ignore-spans
+#![feature(generic_associated_types)]
+
+// This test unsures that with_opt_const_param returns the
+// def_id of the N param in the Foo::Assoc GAT.
+
+trait Foo {
+    type Assoc<const N: usize>;
+    fn foo(
+        &self,
+    ) -> Self::Assoc<{ if cfg!(rpass2) { 3 } else { 2 } }>;
+}
+
+impl Foo for () {
+    type Assoc<const N: usize> = [(); N];
+    fn foo(
+        &self,
+    ) -> Self::Assoc<{ if cfg!(rpass2) { 3 } else { 2 } }> {
+        [(); { if cfg!(rpass2) { 3 } else { 2 } }]
+    }
+}
+
+fn main() {
+    assert_eq!(
+        ().foo(),
+        [(); { if cfg!(rpass2) { 3 } else { 2 } }]
+    );
+}

tests/incremental/const-generics/change-const-param-type.rs

@@ -0,0 +1,68 @@
+// revisions: rpass1 rpass2 rpass3
+// compile-flags: -Zincremental-ignore-spans
+
+enum Foo<const N: usize> {
+    Variant,
+    Variant2(),
+    Variant3 {},
+}
+
+impl Foo<1> {
+    fn foo<const N: usize>(&self) -> [(); N] { [(); N] }
+}
+
+impl Foo<2> {
+    fn foo<const N: u32>(self) -> usize { N as usize }
+}
+
+struct Bar<const N: usize>;
+struct Bar2<const N: usize>();
+struct Bar3<const N: usize> {}
+
+#[cfg(rpass1)]
+struct ChangingStruct<const N: usize>;
+
+#[cfg(any(rpass2, rpass3))]
+struct ChangingStruct<const N: u32>;
+
+struct S;
+
+impl S {
+    #[cfg(rpass1)]
+    fn changing_method<const N: usize>(self) {}
+
+    #[cfg(any(rpass2, rpass3))]
+    fn changing_method<const N: u32>(self) {}
+}
+
+// We want to verify that all goes well when the value of the const argument change.
+// To avoid modifying `main`'s HIR, we use a separate constant, and use `{ FOO_ARG + 1 }`
+// inside the body to keep having an `AnonConst` to compute.
+const FOO_ARG: usize = if cfg!(rpass2) { 1 } else { 0 };
+
+fn main() {
+    let foo = Foo::Variant::<{ FOO_ARG + 1 }>;
+    foo.foo::<{ if cfg!(rpass3) { 3 } else { 4 } }>();
+
+    let foo = Foo::Variant2::<{ FOO_ARG + 1 }>();
+    foo.foo::<{ if cfg!(rpass3) { 3 } else { 4 } }>();
+
+    let foo = Foo::Variant3::<{ FOO_ARG + 1 }> {};
+    foo.foo::<{ if cfg!(rpass3) { 3 } else { 4 } }>();
+
+    let foo = Foo::<{ FOO_ARG + 1 }>::Variant;
+    foo.foo::<{ if cfg!(rpass3) { 3 } else { 4 } }>();
+
+    let foo = Foo::<{ FOO_ARG + 1 }>::Variant2();
+    foo.foo::<{ if cfg!(rpass3) { 3 } else { 4 } }>();
+
+    let foo = Foo::<{ FOO_ARG + 1 }>::Variant3 {};
+    foo.foo::<{ if cfg!(rpass3) { 3 } else { 4 } }>();
+
+    let _ = Bar::<{ FOO_ARG + 1 }>;
+    let _ = Bar2::<{ FOO_ARG + 1 }>();
+    let _ = Bar3::<{ FOO_ARG + 1 }> {};
+
+    let _ = ChangingStruct::<{ 5 }>;
+    let _ = S.changing_method::<{ 5 }>();
+}