HIR Typecheck - Separate "error" from "equals" in coercion checking

This fixes some incorrect enumeration/checking of ivar possibilities

src/hir_typeck/expr_cs.cpp

@@ -4030,6 +4030,7 @@ namespace {
  enum CoerceResult {
  Unknown, // Coercion still unknown.
  Equality, // Types should be equated
+ Fail, // Equality would fail
  Custom, // An op was emitted, and rule is complete
  Unsize, // Emits an _Unsize op
  };
@@ -4055,7 +4056,12 @@ namespace {
  {
  // [T] can't unsize to anything
  DEBUG("Slice can't unsize");
- return CoerceResult::Equality;
+ if( dst.data().is_Slice() || dst.data().is_Infer() ) {
+ return CoerceResult::Equality;
+ }
+ else {
+ return CoerceResult::Fail;
+ }
  }
 
  // Handle ivars specially
@@ -4824,6 +4830,8 @@ namespace {
  // Continue on with coercion (now that node_ptr is updated)
  switch( check_unsize_tys(context, sp, dep->inner, se.inner, context_mut, &node_ptr) )
  {
+ case CoerceResult::Fail:
+ return CoerceResult::Fail;
  case CoerceResult::Unknown:
  // Add new coercion at the new inner point
  if( &node_ptr != node_ptr_ptr )
@@ -4909,6 +4917,8 @@ namespace {
  // Add downcast
  switch( check_unsize_tys(context, sp, dep->inner, se.inner, context_mut, node_ptr_ptr) )
  {
+ case CoerceResult::Fail:
+ return CoerceResult::Fail;
  case CoerceResult::Unknown:
  return CoerceResult::Unknown;
  case CoerceResult::Custom:
@@ -5014,6 +5024,8 @@ namespace {
  // Continue on with coercion (now that node_ptr is updated)
  switch( check_unsize_tys(context, sp, dep->inner, se.inner, context_mut, &node_ptr) )
  {
+ case CoerceResult::Fail:
+ return CoerceResult::Fail;
  case CoerceResult::Unknown:
  // Add new coercion at the new inner point
  if( &node_ptr != node_ptr_ptr )
@@ -5192,6 +5204,8 @@ namespace {
 
  switch( check_coerce_tys(context, sp, ty_dst, ty_src, &context, &node_ptr) )
  {
+ case CoerceResult::Fail:
+ return false;
  case CoerceResult::Unknown:
  DEBUG("Unknown - keep");
  return false;
@@ -5740,9 +5754,17 @@ namespace
 
  switch(check_coerce_tys(context, sp, t_l, t_r, nullptr, bound->right_node_ptr))
  {
+ case CoerceResult::Fail:
+ DEBUG("Fail - Invalid");
+ return true;
  case CoerceResult::Unsize:
+ DEBUG("Unsize - Valid");
+ break;
  case CoerceResult::Unknown:
+ DEBUG("Unknown?");
+ break;
  case CoerceResult::Custom:
+ DEBUG("Custom");
  break;
  case CoerceResult::Equality:
  // NOTE: looking for strict inequality (fuzzy is allowed)
@@ -5785,6 +5807,8 @@ namespace
  case CoerceResult::Unknown:
  case CoerceResult::Custom:
  break;
+ case CoerceResult::Fail:
+ return true;
  case CoerceResult::Equality:
  // NOTE: looking for strict inequality (fuzzy is allowed)
  DEBUG("Check " << pty.ty << " == " << new_ty);