Implement @extern

A more targeted version of --allow-undefined

Author: WardBrian

src/frontend/Environment.ml

@@ -21,6 +21,7 @@ type info =
   ; kind:
       [ `Variable of varinfo
       | `UserDeclared of Location_span.t
+      | `UserExtern of Location_span.t
       | `StanMath
       | `UserDefined ] }
 [@@deriving sexp]

src/frontend/Environment.mli

@@ -21,6 +21,7 @@ type info =
   ; kind:
       [ `Variable of varinfo
       | `UserDeclared of Location_span.t
+      | `UserExtern of Location_span.t
       | `StanMath
       | `UserDefined ] }
 
@@ -37,6 +38,7 @@ val add :
   -> string
   -> Middle.UnsizedType.t
   -> [ `UserDeclared of Location_span.t
+     | `UserExtern of Location_span.t
      | `StanMath
      | `UserDefined
      | `Variable of varinfo ]

src/frontend/Typechecker.ml

@@ -292,14 +292,14 @@ let check_id cf loc tenv id =
       Semantic_error.invalid_unnormalized_fn loc |> error
   | {kind= `Variable {origin; _}; type_} :: _ ->
       (calculate_autodifftype cf origin type_, type_)
-  | { kind= `UserDefined | `UserDeclared _
+  | { kind= `UserDefined | `UserExtern _ | `UserDeclared _
     ; type_= UFun (args, rt, FnLpdf _, mem_pattern) }
     :: _ ->
       let type_ =
         UnsizedType.UFun
           (args, rt, Fun_kind.suffix_from_name id.name, mem_pattern) in
       (calculate_autodifftype cf Functions type_, type_)
-  | {kind= `UserDefined | `UserDeclared _; type_} :: _ ->
+  | {kind= `UserDefined | `UserExtern _ | `UserDeclared _; type_} :: _ ->
       (calculate_autodifftype cf Functions type_, type_)
 
 let check_variable cf loc tenv id =
@@ -1177,7 +1177,8 @@ let verify_assignable_id loc cf tenv assign_id =
     | {kind= `Variable {origin; global; readonly}; _} :: _ ->
         (origin, global, readonly)
     | {kind= `StanMath; _} :: _ -> (MathLibrary, true, false)
-    | {kind= `UserDefined | `UserDeclared _; _} :: _ -> (Functions, true, false)
+    | {kind= `UserDefined | `UserDeclared _ | `UserExtern _; _} :: _ ->
+        (Functions, true, false)
     | _ ->
         Semantic_error.ident_not_in_scope loc assign_id.name
           (Env.nearest_ident tenv assign_id.name)
@@ -1727,11 +1728,13 @@ and verify_fundef_overloaded loc tenv id arg_tys rt =
     verify_unique_signature tenv loc id arg_tys rt;
   verify_name_fresh tenv id ~is_udf:true
 
-and get_fn_decl_or_defn loc tenv id arg_tys rt body =
+and get_fn_decl_or_defn loc tenv id arg_tys rt body annotations =
   match body with
   | {stmt= Skip; _} ->
       if exists_matching_fn_declared tenv id arg_tys rt then
         Semantic_error.fn_decl_exists loc id.name |> error
+      else if List.mem annotations "extern" ~equal:String.equal then
+        `UserExtern id.id_loc
       else `UserDeclared id.id_loc
   | _ -> `UserDefined
 
@@ -1909,13 +1912,13 @@ let add_userdefined_functions tenv stmts_opt =
   | Some {stmts; _} ->
       let f tenv (s : Ast.untyped_statement) =
         match s with
-        | { stmt= FunDef {returntype; funname; arguments; body; annotations= _}
+        | { stmt= FunDef {returntype; funname; arguments; body; annotations}
           ; smeta= {loc} } ->
             let arg_types = Ast.type_of_arguments arguments in
             verify_fundef_overloaded loc tenv funname arg_types returntype;
             let defined =
               get_fn_decl_or_defn loc tenv funname arg_types returntype body
-            in
+                annotations in
             add_function tenv funname.name
               (UFun
                  ( arg_types

src/stan_math_backend/Transform_Mir.ml

@@ -1012,7 +1012,7 @@ let map_prog_stmt_lists f (p : ('a, 'b, 'c) Program.t) =
   ; transform_inits= f p.transform_inits
   ; unconstrain_array= f p.unconstrain_array }
 
-let recognized_annotation _ = false
+let recognized_annotation a = a = "extern"
 
 let trans_prog (p : Program.Typed.t) =
   (* name mangling of c++ keywords*)

test/integration/bad/function-signatures/overloading/define_extern1.stan

@@ -0,0 +1,7 @@
+functions {
+  @extern real foo(int x, int y);
+  real foo(int x, int y){
+    return 1.0;
+  }
+
+}

test/integration/bad/function-signatures/overloading/define_extern2.stan

@@ -0,0 +1,4 @@
+functions {
+  @extern real foo(int x, int y);
+  real foo(int x, int y);
+}

test/integration/bad/function-signatures/overloading/stanc.expected

@@ -1,3 +1,25 @@
+  $ ../../../../../../install/default/bin/stanc define_extern1.stan
+Semantic error in 'define_extern1.stan', line 2, column 33 to line 5, column 3:
+   -------------------------------------------------
+     1:  functions {
+     2:    @extern real foo(int x, int y);
+                                          ^
+     3:    real foo(int x, int y){
+     4:      return 1.0;
+   -------------------------------------------------
+
+Function 'foo' has already been declared for signature (int, int) => real
+  $ ../../../../../../install/default/bin/stanc define_extern2.stan
+Semantic error in 'define_extern2.stan', line 2, column 33 to line 3, column 25:
+   -------------------------------------------------
+     1:  functions {
+     2:    @extern real foo(int x, int y);
+                                          ^
+     3:    real foo(int x, int y);
+     4:  }
+   -------------------------------------------------
+
+Function 'foo' has already been declared for signature (int, int) => real
   $ ../../../../../../install/default/bin/stanc no_minimum_dae.stan
 Semantic error in 'no_minimum_dae.stan', line 38, column 12 to column 59:
    -------------------------------------------------

test/integration/good/lang/good_annotations.stan

@@ -1,4 +1,6 @@
 functions {
+  @extern real foo(int x, int y);
+
   @foo @biz void bar(int x, int y, int z, int w, int a, int b, int d, int e, int f){
     print(x);
   }

test/integration/good/lang/pretty.expected

@@ -17,6 +17,8 @@ model {
 
   $ ../../../../../install/default/bin/stanc --auto-format good_annotations.stan
 functions {
+  @extern real foo(int x, int y);
+  
   @foo
   @biz
   void bar(int x, int y, int z, int w, int a, int b, int d, int e, int f) {
@@ -35,19 +37,19 @@ generated quantities {
   matrix[34, 10000] a_bit_too_long = rep_matrix(1, 34, 10000);
 }
 
-Warning in 'good_annotations.stan', line 2, column 17: Unknown annotation
+Warning in 'good_annotations.stan', line 4, column 17: Unknown annotation
     'foo' will be ignored by the compiler
-Warning in 'good_annotations.stan', line 2, column 17: Unknown annotation
+Warning in 'good_annotations.stan', line 4, column 17: Unknown annotation
     'biz' will be ignored by the compiler
-Warning in 'good_annotations.stan', line 7, column 19: Unknown annotation
+Warning in 'good_annotations.stan', line 9, column 19: Unknown annotation
     'baz' will be ignored by the compiler
-Warning in 'good_annotations.stan', line 12, column 89: Unknown annotation
+Warning in 'good_annotations.stan', line 14, column 89: Unknown annotation
     'bar' will be ignored by the compiler
-Warning in 'good_annotations.stan', line 12, column 89: Unknown annotation
+Warning in 'good_annotations.stan', line 14, column 89: Unknown annotation
     'baz' will be ignored by the compiler
-Warning in 'good_annotations.stan', line 12, column 89: Unknown annotation
+Warning in 'good_annotations.stan', line 14, column 89: Unknown annotation
     'flux' will be ignored by the compiler
-Warning in 'good_annotations.stan', line 12, column 89: Unknown annotation
+Warning in 'good_annotations.stan', line 14, column 89: Unknown annotation
     'really_extra_long_now' will be ignored by the compiler
   $ ../../../../../install/default/bin/stanc --auto-format good_const.stan
 transformed data {