Add some tests for constraints depending on resolving other constraints (#5885)

Questions of what should be possible are raised in
#5884

This provides the examples from the issue as test cases.

Author: danakj

toolchain/check/testdata/facet/early_rewrites.carbon

@@ -0,0 +1,95 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// INCLUDE-FILE: toolchain/testing/testdata/min_prelude/facet_types.carbon
+//
+// AUTOUPDATE
+// TIP: To test this file alone, run:
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/facet/early_rewrites.carbon
+// TIP: To dump output, run:
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/facet/early_rewrites.carbon
+
+// Tests where `ImplWitnessAccess` on the RHS of a rewrite constraint is used in
+// other constraints within the same facet type in ways that require the RHS to
+// be evaluated to a concrete value before the facet type is resolved (such as
+// by passing it as a parameter to a generic class).
+
+// --- nested_constraint_visible_in_type_parameter.carbon
+library "[[@TEST_NAME]]";
+
+interface Z {
+  let Z1:! type;
+  let Z2:! type;
+}
+
+class C(T:! Z where .Z1 = ()) {}
+
+interface J {
+  let J1:! (Z where .Z1 = ()) where .Z2 = C(.Self);
+}
+
+// --- todo_earlier_constraint_visible_in_type_parameter.carbon
+library "[[@TEST_NAME]]";
+
+interface Z {
+  let Z1:! type;
+  let Z2:! type;
+}
+
+class C(T:! Z where .Z1 = ()) {}
+
+// TODO: Should this pass? Or do we need a `where` between .Z1 and .Z2 to make
+// .Z1's value visible to .Z2?
+// See https://github.com/carbon-language/carbon-lang/issues/5884.
+interface J {
+  let J1:! Z where .Z1 = () and .Z2 = C(.Self);
+}
+
+// --- todo_later_constraint_visible_in_type_parameter.carbon
+library "[[@TEST_NAME]]";
+
+interface Z {
+  let Z1:! type;
+  let Z2:! type;
+}
+
+class C(T:! Z where .Z1 = ()) {}
+
+// TODO: Should this pass? Or do we need a `where` between .Z1 and .Z2 to make
+// .Z1's value visible to .Z2?
+// See https://github.com/carbon-language/carbon-lang/issues/5884.
+interface J {
+  let J1:! Z where .Z2 = C(.Self) and .Z1 = ();
+}
+
+// --- fail_todo_resolved_constraint_visible_in_type_parameter.carbon
+library "[[@TEST_NAME]]";
+
+interface Y {
+  let Y1:! type;
+}
+
+interface Z {
+  let Z1:! Y;
+  let Z2:! type;
+  let Z3:! type;
+}
+
+interface Tuple {}
+impl () as Tuple {}
+class C(T:! Tuple) {}
+
+// TODO: Should this pass? Or do we need a `where` between .Z2 and .Z3 to make
+// .Z2's value visible to .Z3?
+// See https://github.com/carbon-language/carbon-lang/issues/5884.
+interface J {
+  // CHECK:STDERR: fail_todo_resolved_constraint_visible_in_type_parameter.carbon:[[@LINE+7]]:80: error: cannot convert type `.(Z.Z2)` into type implementing `Tuple` [ConversionFailureTypeToFacet]
+  // CHECK:STDERR:   let J1:! (Z & Y where .Y1 = ()) where .Z1 = .Self and .Z2 = .Z1.Y1 and .Z3 = C(.Z2);
+  // CHECK:STDERR:                                                                                ^~~~~~
+  // CHECK:STDERR: fail_todo_resolved_constraint_visible_in_type_parameter.carbon:[[@LINE-9]]:9: note: initializing generic parameter `T` declared here [InitializingGenericParam]
+  // CHECK:STDERR: class C(T:! Tuple) {}
+  // CHECK:STDERR:         ^
+  // CHECK:STDERR:
+  let J1:! (Z & Y where .Y1 = ()) where .Z1 = .Self and .Z2 = .Z1.Y1 and .Z3 = C(.Z2);
+}