Remove child-reentrance special-case in CABI

Author: lukewagner

design/mvp/CanonicalABI.md

@@ -1603,13 +1603,11 @@ When instantiating component instance `$inst`:
 
 where `canon_lower` is defined:
 ```python
-def canon_lower(opts, inst, callee, calling_import, ft, flat_args):
+def canon_lower(opts, inst, callee, ft, flat_args):
   import_call = ImportCall(opts, inst)
   trap_if(not inst.may_leave)
-
   assert(inst.may_enter)
-  if calling_import:
-    inst.may_enter = False
+  inst.may_enter = False
 
   flat_args = CoreValueIter(flat_args)
   flat_results = None
@@ -1623,9 +1621,7 @@ def canon_lower(opts, inst, callee, calling_import, ft, flat_args):
 
   callee(start_thunk, return_thunk)
 
-  if calling_import:
-    inst.may_enter = True
-
+  inst.may_enter = True
   import_call.exit()
   return flat_results
 ```
@@ -1638,17 +1634,10 @@ as post-MVP [adapter functions].
 
 By clearing `may_enter` for the duration of calls to imports, the `may_enter`
 guard in `canon_lift` ensures that components cannot be externally reentered,
-which is part of the [component invariants]. The `calling_import` condition
-allows a parent component to call into a child component (which is, by
-definition, not a call to an import) and for the child to then reenter the
-parent through a function the parent explicitly supplied to the child's
-`instantiate`. This form of internal reentrance allows the parent to fully
-virtualize the child's imports.
-
-Because `may_enter` is not cleared on the exceptional exit path taken by
-`trap()`, if there is a trap during Core WebAssembly execution of lifting or
-lowering, the component is left permanently un-enterable, ensuring the
-lockdown-after-trap [component invariant].
+which is part of the [component invariants]. Because `may_enter` is not cleared
+on the exceptional exit path taken by `trap()`, if there is a trap during Core
+WebAssembly execution of lifting or lowering, the component is left permanently
+un-enterable, ensuring the lockdown-after-trap [component invariant].
 
 ### `canon resource.new`
 

design/mvp/canonical-abi/definitions.py

@@ -1148,13 +1148,11 @@ def call_and_trap_on_throw(callee, args):
 
 ### `canon lower`
 
-def canon_lower(opts, inst, callee, calling_import, ft, flat_args):
+def canon_lower(opts, inst, callee, ft, flat_args):
   import_call = ImportCall(opts, inst)
   trap_if(not inst.may_leave)
-
   assert(inst.may_enter)
-  if calling_import:
-    inst.may_enter = False
+  inst.may_enter = False
 
   flat_args = CoreValueIter(flat_args)
   flat_results = None
@@ -1168,9 +1166,7 @@ def return_thunk(results):
 
   callee(start_thunk, return_thunk)
 
-  if calling_import:
-    inst.may_enter = True
-
+  inst.may_enter = True
   import_call.exit()
   return flat_results
 

design/mvp/canonical-abi/run_tests.py

@@ -1,6 +1,6 @@
 import definitions
-from functools import partial
 from definitions import *
+from functools import partial
 
 def equal_modulo_string_encoding(s, t):
   if s is None and t is None:
@@ -353,7 +353,7 @@ def test_roundtrip(t, v):
   flat_args = lower_values(caller_cx, definitions.MAX_FLAT_PARAMS, [v], [t])
   if return_in_heap:
     flat_args += [ caller_heap.realloc(0, 0, alignment(t), elem_size(t)) ]
-  flat_results = canon_lower(caller_opts, caller_inst, lifted_callee, True, ft, flat_args)
+  flat_results = canon_lower(caller_opts, caller_inst, lifted_callee, ft, flat_args)
   if return_in_heap:
     flat_results = [ flat_args[-1] ]
   [got] = lift_values(caller_cx, definitions.MAX_FLAT_PARAMS, CoreValueIter(flat_results), [t])
@@ -420,7 +420,7 @@ def core_wasm(args):
       1,
       3
     ]
-    results = canon_lower(opts, inst, host_import, True, host_ft, args)
+    results = canon_lower(opts, inst, host_import, host_ft, args)
     assert(len(results) == 1)
     assert(results[0] == 4)
     assert(canon_resource_rep(inst, rt, 4)[0] == 45)