Auto-recover constructor expressions (#4124)

This PR adds checks when assigning a constructor expression or passing one as a parameter to see if it can be auto-recovered, and if so, does not output a subtyping error. E.g. for the following code:

```
actor Main
  new create(env: Env) =>
    Bar.take_foo(Foo(88))
    let bar: Foo iso = Foo(88)

class Foo
  new create(v: U8) =>
    None

primitive Bar
  fun take_foo(foo: Foo iso) =>
    None
```

We'd previously get errors on both lines in Main.create(); whereas with this PR they are now accepted.

Fixes #702


Co-authored-by: Sean T Allen <sean@seantallen.com>
Co-authored-by: Jason Carr <jcarr250@protonmail.com>

.release-notes/4124.md

@@ -0,0 +1,24 @@
+## Allow constructor expressions to be auto-recovered in assignments or arguments
+
+Previously for the following code:
+
+```pony
+actor Main
+  new create(env: Env) =>
+    Bar.take_foo(Foo(88))
+    let bar: Foo iso = Foo(88)
+
+class Foo
+  new create(v: U8) =>
+    None
+
+primitive Bar
+  fun take_foo(foo: Foo iso) =>
+    None
+```
+
+You'd get compilation errors "argument not assignable to parameter" and "right side must be a subtype of left side" for the two lines in `Main.create()`.
+
+We've added checks to see if the constructor expressions can be implicitly auto-recovered, and if they can, no compilation error is generated.
+
+This only applies to cases where the type of the parameter (or the `let` binding) is a simple type, i.e. not a union, intersection or tuple type.

src/libponyc/expr/call.c

@@ -195,6 +195,54 @@ static bool apply_default_arg(pass_opt_t* opt, ast_t* param, ast_t** argp)
   return true;
 }
 
+static ast_t* method_receiver_type(ast_t* method);
+
+bool check_auto_recover_newref(ast_t* dest_type, ast_t* ast)
+{
+  // we're not going to try auto-recovering to a complex type
+  if (ast_id(dest_type) != TK_NOMINAL)
+    return false;
+
+  while (ast != NULL && ast_id(ast) != TK_CALL)
+    ast = ast_child(ast);
+
+  if (ast == NULL)
+    return false;
+
+  AST_GET_CHILDREN(ast, newref, positional, named);
+  if (ast_id(newref) != TK_NEWREF)
+    return false;
+
+  // sometimes for assignments there's a nested newref
+  ast_t* child = ast_child(newref);
+  if (child != NULL && ast_id(child) == TK_NEWREF)
+    newref = child;
+
+  ast_t* receiver_type = method_receiver_type(newref);
+  token_id rcap = ast_id(cap_fetch(receiver_type));
+  if (!(rcap == TK_REF || rcap == TK_BOX))
+    return false;
+
+  ast_t* arg = ast_child(positional);
+  while (arg != NULL)
+  {
+    ast_t* arg_type = ast_type(arg);
+    if (is_typecheck_error(arg_type))
+      return false;
+
+    ast_t* arg_type_aliased = alias(arg_type);
+    bool ok = safe_to_autorecover(dest_type, arg_type_aliased, WRITE);
+    ast_free_unattached(arg_type_aliased);
+
+    if (!ok)
+      return false;
+
+    arg = ast_sibling(arg);
+  }
+
+  return true;
+}
+
 static bool check_arg_types(pass_opt_t* opt, ast_t* params, ast_t* positional,
   bool partial, bool is_bare)
 {
@@ -236,8 +284,15 @@ static bool check_arg_types(pass_opt_t* opt, ast_t* params, ast_t* positional,
       return false;
     }
 
-    ast_t* wp_type = consume_type(p_type, TK_NONE, false);
     errorframe_t info = NULL;
+    ast_t* wp_type = consume_type(p_type, TK_NONE, false);
+    if(check_auto_recover_newref(wp_type, arg))
+    {
+      token_id arg_cap = ast_id(cap_fetch(wp_type));
+      ast_t* recovered_arg_type = recover_type(arg_type, arg_cap);
+      if (recovered_arg_type)
+        arg_type = recovered_arg_type;
+    }
 
     if(wp_type == NULL)
     {

src/libponyc/expr/call.h

@@ -8,6 +8,7 @@
 PONY_EXTERN_C_BEGIN
 
 bool method_check_type_params(pass_opt_t* opt, ast_t** astp);
+bool check_auto_recover_newref(ast_t* dest_type, ast_t* ast);
 
 bool expr_call(pass_opt_t* opt, ast_t** astp);
 

src/libponyc/expr/operator.c

@@ -3,6 +3,7 @@
 #include "postfix.h"
 #include "control.h"
 #include "reference.h"
+#include "call.h"
 #include "../ast/astbuild.h"
 #include "../ast/id.h"
 #include "../ast/lexer.h"
@@ -373,7 +374,15 @@ bool expr_assign(pass_opt_t* opt, ast_t* ast)
 
     default: {}
   }
+
   ast_t* wl_type = consume_type(fl_type, TK_NONE, false);
+  if(check_auto_recover_newref(fl_type, right))
+  {
+    token_id left_cap = ast_id(cap_fetch(wl_type));
+    ast_t* recovered_left_type = recover_type(r_type, left_cap);
+    if (recovered_left_type)
+      r_type = recovered_left_type;
+  }
 
   // Assignment is based on the alias of the right hand side.
   errorframe_t info = NULL;

src/libponyc/type/cap.c

@@ -950,6 +950,9 @@ bool cap_safetomove(token_id into, token_id cap, direction direction)
       break;
 
     case TK_TRN:
+    // when recovering to val, anything which has no
+    // writable aliases elsewhere is fine
+    case TK_VAL:
       switch(cap)
       {
         case TK_ISO:
@@ -1012,15 +1015,13 @@ bool cap_immutable_or_opaque(token_id cap)
   return false;
 }
 
-
-
 static ast_t* modified_cap_single(ast_t* type, cap_mutation* mutation)
 {
   ast_t* cap = cap_fetch(type);
   ast_t* ephemeral = ast_sibling(cap);
 
   token_id cap_token = ast_id(cap);
-  token_id eph_token = ast_id(cap);
+  token_id eph_token = ast_id(ephemeral);
 
   if (mutation(&cap_token, &eph_token))
   {
@@ -1153,4 +1154,3 @@ ast_t* unisolated(ast_t* type)
 {
   return modified_cap(type, unisolated_mod);
 }
-

test/libponyc-run/ctor-autorecover/main.pony

@@ -0,0 +1,38 @@
+actor Main
+  new create(env: Env) =>
+    // zero-parameter constructor as argument and assignment
+    Bar.take_foo(Foo)
+    Bar.take_foo_val(Foo)
+    let qux: Foo iso = Foo
+
+    // sendable-parameter constructor as argument and assignment
+    Bar.take_foo(Foo.from_u8(88))
+    Bar.take_foo_val(Foo.from_u8(88))
+    let bar: Foo iso = Foo.from_u8(88)
+
+    // non-sendable parameter ctor and assignment must fail
+    // see RecoverTest.CantAutoRecover_CtorArgWithNonSendableArg
+    // and RecoverTest.CantAutoRecover_CtorAssignmentWithNonSendableArg
+
+    //let s: String ref = String
+    //Bar.take_foo(Foo.from_str(s)) -> argument not assignable to parameter
+    //let baz: Foo iso = Foo.from_str(s) -> right side must be a subtype of left side
+
+    // verify that inheritance hasn't broken
+    let x = String
+    let y: String ref = x
+
+class Foo
+  new create() =>
+    None
+  new ref from_u8(v: U8) =>
+    None
+  new ref from_str(s: String ref) =>
+    None
+
+primitive Bar
+  fun take_foo(foo: Foo iso) =>
+    None
+
+  fun take_foo_val(foo: Foo val) =>
+    None

test/libponyc/recover.cc

@@ -738,3 +738,171 @@ TEST_F(RecoverTest, CanWriteTrn_TrnAutoRecovery)
 
   TEST_COMPILE(src);
 }
+TEST_F(RecoverTest, LetIso_CtorAutoRecovery)
+{
+  const char* src =
+    "class A\n"
+    "  new ref create() =>\n"
+    "    None\n"
+
+    "actor Main\n"
+    "  new create(env: Env) =>\n"
+    "    let a_iso: A iso = A\n";
+
+  TEST_COMPILE(src);
+}
+TEST_F(RecoverTest, VarIso_CtorAutoRecovery)
+{
+  const char* src =
+    "class A\n"
+    "  new ref create() =>\n"
+    "    None\n"
+
+    "actor Main\n"
+    "  new create(env: Env) =>\n"
+    "    var a_iso: A iso = A\n";
+
+  TEST_COMPILE(src);
+}
+TEST_F(RecoverTest, LetTrn_CtorAutoRecovery)
+{
+  const char* src =
+    "class A\n"
+    "  new ref create() =>\n"
+    "    None\n"
+
+    "actor Main\n"
+    "  new create(env: Env) =>\n"
+    "    var a_trn: A trn = A\n";
+
+  TEST_COMPILE(src);
+}
+TEST_F(RecoverTest, LetVal_RefCtorAutoRecovery)
+{
+  const char* src =
+    "class A\n"
+    "  new ref create() =>\n"
+    "    None\n"
+
+    "actor Main\n"
+    "  new create(env: Env) =>\n"
+    "    var a_val: A val = A\n";
+
+  TEST_COMPILE(src);
+}
+TEST_F(RecoverTest, LetVal_BoxCtorAutoRecovery)
+{
+  const char* src =
+    "class A\n"
+    "  new box create() =>\n"
+    "    None\n"
+
+    "actor Main\n"
+    "  new create(env: Env) =>\n"
+    "    var a_val: A val = A\n";
+
+  TEST_COMPILE(src);
+}
+TEST_F(RecoverTest, LetIso_ArgsCtorAutoRecovery)
+{
+  const char* src =
+    "class A\n"
+    "  new ref create(s: String box) =>\n"
+    "    None\n"
+
+    "actor Main\n"
+    "  new create(env: Env) =>\n"
+    "    let s: String val = \"\"\n"
+    "    let a_iso: A iso = A(s)\n";
+
+  TEST_COMPILE(src);
+}
+TEST_F(RecoverTest, LetTrn_ArgsCtorAutoRecovery)
+{
+  const char* src =
+    "class A\n"
+    "  new ref create(s: String box) =>\n"
+    "    None\n"
+
+    "actor Main\n"
+    "  new create(env: Env) =>\n"
+    "    let s: String val = \"\"\n"
+    "    let a_trn: A trn = A(s)\n";
+
+  TEST_COMPILE(src);
+}
+TEST_F(RecoverTest, LetVal_ArgsCtorAutoRecovery)
+{
+  const char* src =
+    "class A\n"
+    "  new ref create(s: String box) =>\n"
+    "    None\n"
+
+    "actor Main\n"
+    "  new create(env: Env) =>\n"
+    "    let s: String val = \"\"\n"
+    "    let a_val: A val = A(s)\n";
+
+  TEST_COMPILE(src);
+}
+
+
+TEST_F(RecoverTest, CantAutoRecover_CtorArgWithNonSendableArg)
+{
+  const char* src =
+    "actor Main\n"
+    "  new create(env: Env) =>\n"
+    "    let s: String ref = String\n"
+    "    Bar.take_foo(Foo.from_str(s))\n"
+
+    "class Foo\n"
+    "  new from_u8(v: U8) =>\n"
+    "    None\n"
+    "  new from_str(s: String ref) =>\n"
+    "    None\n"
+
+    "primitive Bar\n"
+    "  fun take_foo(foo: Foo iso) =>\n"
+    "    None\n";
+
+  TEST_ERRORS_1(src, "argument not assignable to parameter");
+}
+TEST_F(RecoverTest, CantAutoRecover_CtorAssignmentWithNonSendableArg)
+{
+  const char* src =
+    "actor Main\n"
+    "  new create(env: Env) =>\n"
+    "    let s: String ref = String\n"
+    "    let bar: Foo iso = Foo.from_str(s)\n"
+
+    "class Foo\n"
+    "  new from_u8(v: U8) =>\n"
+    "    None\n"
+    "  new from_str(s: String ref) =>\n"
+    "    None\n"
+
+    "primitive Bar\n"
+    "  fun take_foo(foo: Foo iso) =>\n"
+    "    None\n";
+
+  TEST_ERRORS_1(src, "right side must be a subtype of left side");
+}
+TEST_F(RecoverTest, CantAutoRecover_CtorParamToComplexTypeWithNonSendableArg)
+{
+  const char* src =
+    "actor Main\n"
+    "  new create(env: Env) =>\n"
+    "    let bar: (Foo iso | String ref) = Foo.from_u8(123)\n"
+
+    "class Foo\n"
+    "  new from_u8(v: U8) =>\n"
+    "    None\n"
+    "  new from_str(s: String ref) =>\n"
+    "    None\n"
+
+    "primitive Bar\n"
+    "  fun take_foo(foo: Foo iso) =>\n"
+    "    None\n";
+
+  TEST_ERRORS_1(src, "right side must be a subtype of left side");
+}