From 86d7b36ba751002f534479f005ef220963184878 Mon Sep 17 00:00:00 2001
From: Gaith Hallak <gaithhallak@gmail.com>
Date: Mon, 17 Jul 2023 13:32:11 +0300
Subject: [PATCH] Unify typesigs when implementing interface funs (#469)

---
 CHANGELOG.md                 |  1 +
 src/aeso_ast_infer_types.erl | 19 +++++++++++++------
 test/aeso_compiler_tests.erl |  8 ++++----
 3 files changed, 18 insertions(+), 10 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 998354f..52bf16f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Changed
 ### Removed
 ### Fixed
+- Fixed a bug with polymorphism that allowed functions with the same name but different type to be considered as implementations for their corresponding interface function.
 
 ## [7.2.1]
 ### Fixed
diff --git a/src/aeso_ast_infer_types.erl b/src/aeso_ast_infer_types.erl
index 6a71813..d74358b 100644
--- a/src/aeso_ast_infer_types.erl
+++ b/src/aeso_ast_infer_types.erl
@@ -1582,7 +1582,7 @@ check_reserved_entrypoints(Funs) ->
 check_fundecl(Env, {fun_decl, Ann, Id = {id, _, Name}, Type = {fun_t, _, _, _, _}}) ->
     Type1 = {fun_t, _, Named, Args, Ret} = check_type(Env, Type),
     TypeSig = {type_sig, Ann, none, Named, Args, Ret},
-    register_implementation(Id, TypeSig),
+    register_implementation(Env, Id, TypeSig),
     {{Name, TypeSig}, {fun_decl, Ann, Id, Type1}};
 check_fundecl(Env, {fun_decl, Ann, Id = {id, _, Name}, Type}) ->
     type_error({fundecl_must_have_funtype, Ann, Id, Type}),
@@ -1590,13 +1590,16 @@ check_fundecl(Env, {fun_decl, Ann, Id = {id, _, Name}, Type}) ->
 
 %% Register the function FunId as implemented by deleting it from the functions
 %% to be implemented table if it is included there, or return true otherwise.
--spec register_implementation(FunId, FunSig) -> true | no_return() when
+-spec register_implementation(env(), FunId, FunSig) -> true | no_return() when
       FunId :: aeso_syntax:id(),
       FunSig :: typesig().
-register_implementation(Id, Sig) ->
+register_implementation(Env, Id, Sig) ->
     Name = name(Id),
     case ets_lookup(functions_to_implement, Name) of
-        [{Name, Interface, Decl = {fun_decl, _, DeclId, _}}] ->
+        [{Name, Interface, Decl = {fun_decl, _, DeclId, FunT}}] ->
+            When = {implement_interface_fun, aeso_syntax:get_ann(Sig), Name, name(Interface)},
+            unify(Env, typesig_to_fun_t(Sig), FunT, When),
+
             DeclStateful   = aeso_syntax:get_ann(stateful,   Decl, false),
             DeclPayable    = aeso_syntax:get_ann(payable,    Decl, false),
 
@@ -1624,7 +1627,7 @@ infer_nonrec(Env, LetFun) ->
     create_constraints(),
     NewLetFun = {{_, Sig}, _} = infer_letfun(Env, LetFun),
     check_special_funs(Env, NewLetFun),
-    register_implementation(get_letfun_id(LetFun), Sig),
+    register_implementation(Env, get_letfun_id(LetFun), Sig),
     solve_then_destroy_and_report_unsolved_constraints(Env),
     Result = {TypeSig, _} = instantiate(NewLetFun),
     print_typesig(TypeSig),
@@ -1654,7 +1657,7 @@ infer_letrec(Env, Defs) ->
     Inferred =
         [ begin
             Res    = {{Name, TypeSig}, LetFun} = infer_letfun(ExtendEnv, LF),
-            register_implementation(get_letfun_id(LetFun), TypeSig),
+            register_implementation(Env, get_letfun_id(LetFun), TypeSig),
             Got    = proplists:get_value(Name, Funs),
             Expect = typesig_to_fun_t(TypeSig),
             unify(Env, Got, Expect, {check_typesig, Name, Got, Expect}),
@@ -4165,6 +4168,10 @@ pp_when({var_args, Ann, Fun}) ->
     {pos(Ann)
     , io_lib:format("when resolving arguments of variadic function `~s`", [pp_expr(Fun)])
     };
+pp_when({implement_interface_fun, Ann, Entrypoint, Interface}) ->
+    { pos(Ann)
+    , io_lib:format("when implementing the entrypoint `~s` from the interface `~s`", [Entrypoint, Interface])
+    };
 pp_when(unknown) -> {pos(0,0), ""}.
 
 -spec pp_why_record(why_record()) -> {pos(), iolist()}.
diff --git a/test/aeso_compiler_tests.erl b/test/aeso_compiler_tests.erl
index ed50821..fc47629 100644
--- a/test/aeso_compiler_tests.erl
+++ b/test/aeso_compiler_tests.erl
@@ -871,10 +871,10 @@ failing_contracts() ->
                      "Trying to implement or extend an undefined interface `Z`">>
                   ])
     , ?TYPE_ERROR(polymorphism_contract_interface_same_name_different_type,
-                  [<<?Pos(9,5)
-                     "Duplicate definitions of `f` at\n"
-                     "  - line 8, column 5\n"
-                     "  - line 9, column 5">>])
+                  [<<?Pos(5,5)
+                     "Cannot unify `char` and `int`\n"
+                     "when implementing the entrypoint `f` from the interface `I1`">>
+                  ])
     , ?TYPE_ERROR(polymorphism_contract_missing_implementation,
                   [<<?Pos(4,20)
                      "Unimplemented entrypoint `f` from the interface `I1` in the contract `I2`">>