Better error messages for incomplete probability calls

src/frontend/Semantic_check.ml

@@ -290,9 +290,32 @@ let semantic_check_fn_normal ~is_cond_dist ~loc id es =
     | Some _ ->
         (* Check that Funaps are actually functions *)
         Semantic_error.returning_fn_expected_nonfn_found loc id.name |> error
-    | None ->
-        Semantic_error.returning_fn_expected_undeclaredident_found loc id.name
-        |> error)
+    | None -> (
+      match List.rev (String.split id.name ~on:'_') with
+      | suffix :: tl
+        when List.mem Utils.cumulative_distribution_suffices_w_rng suffix
+               ~equal:String.equal ->
+          let prefix = String.concat ~sep:"_" (List.rev tl) in
+          let known_families =
+            List.map
+              ~f:(fun (_, y, _, _) -> y)
+              Stan_math_signatures.distributions
+          in
+          let is_known_family s =
+            List.mem known_families s ~equal:String.equal
+          in
+          if is_known_family prefix then
+            Semantic_error.returning_fn_expected_undeclared_dist_suffix_found
+              loc (prefix, suffix)
+            |> error
+          else
+            Semantic_error.returning_fn_expected_undeclaredident_found loc
+              id.name
+            |> error
+      | _ ->
+          Semantic_error.returning_fn_expected_undeclaredident_found loc
+            id.name
+          |> error ))
 
 (* Stan-Math function application *)
 let semantic_check_fn_stan_math ~is_cond_dist ~loc id es =

src/middle/Semantic_error.ml

@@ -33,6 +33,7 @@ module TypeError = struct
     | ReturningFnExpectedNonReturningFound of string
     | ReturningFnExpectedNonFnFound of string
     | ReturningFnExpectedUndeclaredIdentFound of string
+    | ReturningFnExpectedUndeclaredDistSuffixFound of string * string
     | NonReturningFnExpectedReturningFound of string
     | NonReturningFnExpectedNonFnFound of string
     | NonReturningFnExpectedUndeclaredIdentFound of string
@@ -168,6 +169,13 @@ module TypeError = struct
           "A returning function was expected but an undeclared identifier \
            '%s' was supplied."
           fn_name
+    | ReturningFnExpectedUndeclaredDistSuffixFound (prefix, suffix) ->
+        Fmt.pf ppf
+          "A function was expected but an unknown identifier %s was recieved. \
+           This appears to be part of the %s family of distributions, for \
+           which the %s suffix in not implemented."
+          (String.concat ~sep:"_" [prefix; suffix])
+          prefix suffix
     | NonReturningFnExpectedUndeclaredIdentFound fn_name ->
         Fmt.pf ppf
           "A non-returning function was expected but an undeclared identifier \
@@ -496,6 +504,12 @@ let returning_fn_expected_nonfn_found loc name =
 let returning_fn_expected_undeclaredident_found loc name =
   TypeError (loc, TypeError.ReturningFnExpectedUndeclaredIdentFound name)
 
+let returning_fn_expected_undeclared_dist_suffix_found loc (prefix, suffix) =
+  TypeError
+    ( loc
+    , TypeError.ReturningFnExpectedUndeclaredDistSuffixFound (prefix, suffix)
+    )
+
 let nonreturning_fn_expected_returning_found loc name =
   TypeError (loc, TypeError.NonReturningFnExpectedReturningFound name)
 

src/middle/Semantic_error.mli

@@ -34,6 +34,9 @@ val returning_fn_expected_nonfn_found : Location_span.t -> string -> t
 val returning_fn_expected_undeclaredident_found :
   Location_span.t -> string -> t
 
+val returning_fn_expected_undeclared_dist_suffix_found :
+  Location_span.t -> string * string -> t
+
 val illtyped_reduce_sum :
      Location_span.t
   -> string

src/middle/Utils.ml

@@ -12,6 +12,11 @@ let conditioning_suffices =
   ["_lpdf"; "_lupdf"; "_lupmf"; "_lpmf"; "_cdf"; "_lcdf"; "_lccdf"]
 
 let conditioning_suffices_w_log = conditioning_suffices @ ["_log"]
+let cumulative_distribution_suffices = ["cdf"; "lcdf"; "lccdf"]
+
+let cumulative_distribution_suffices_w_rng =
+  cumulative_distribution_suffices @ ["rng"]
+
 let is_user_ident = Fn.non (String.is_suffix ~suffix:"__")
 
 let unnormalized_suffix = function

test/integration/bad/missing_dist_suffix/dune

@@ -0,0 +1 @@
+(include ../dune)

test/integration/bad/missing_dist_suffix/non_existing_distribution_suffix1.stan

@@ -0,0 +1,5 @@
+data { 
+}
+model {  
+    target += von_mises_cdf(1|0,1);
+}

test/integration/bad/missing_dist_suffix/non_existing_distribution_suffix2.stan

@@ -0,0 +1,5 @@
+data { 
+}
+model {  
+    target += von_mises_lcdf(1|0,1);
+}

test/integration/bad/missing_dist_suffix/non_existing_distribution_suffix3.stan

@@ -0,0 +1,5 @@
+data { 
+}
+model {  
+    target += von_mises_lccdf(1|0,1);
+}

test/integration/bad/missing_dist_suffix/non_existing_distribution_suffix4.stan

@@ -0,0 +1,5 @@
+data { 
+}
+model {  
+    target += von_mises_notasuffix(1|0,1);
+}

test/integration/bad/missing_dist_suffix/stanc.expected

@@ -0,0 +1,44 @@
+  $ ../../../../../install/default/bin/stanc non_existing_distribution_suffix1.stan
+Semantic error in 'non_existing_distribution_suffix1.stan', line 4, column 14 to column 34:
+   -------------------------------------------------
+     2:  }
+     3:  model {  
+     4:      target += von_mises_cdf(1|0,1);
+                       ^
+     5:  }
+   -------------------------------------------------
+
+A function was expected but an unknown identifier von_mises_cdf was recieved. This appears to be part of the von_mises family of distributions, for which the cdf suffix in not implemented.
+  $ ../../../../../install/default/bin/stanc non_existing_distribution_suffix2.stan
+Semantic error in 'non_existing_distribution_suffix2.stan', line 4, column 14 to column 35:
+   -------------------------------------------------
+     2:  }
+     3:  model {  
+     4:      target += von_mises_lcdf(1|0,1);
+                       ^
+     5:  }
+   -------------------------------------------------
+
+A function was expected but an unknown identifier von_mises_lcdf was recieved. This appears to be part of the von_mises family of distributions, for which the lcdf suffix in not implemented.
+  $ ../../../../../install/default/bin/stanc non_existing_distribution_suffix3.stan
+Semantic error in 'non_existing_distribution_suffix3.stan', line 4, column 14 to column 36:
+   -------------------------------------------------
+     2:  }
+     3:  model {  
+     4:      target += von_mises_lccdf(1|0,1);
+                       ^
+     5:  }
+   -------------------------------------------------
+
+A function was expected but an unknown identifier von_mises_lccdf was recieved. This appears to be part of the von_mises family of distributions, for which the lccdf suffix in not implemented.
+  $ ../../../../../install/default/bin/stanc non_existing_distribution_suffix4.stan
+Semantic error in 'non_existing_distribution_suffix4.stan', line 4, column 14 to column 41:
+   -------------------------------------------------
+     2:  }
+     3:  model {  
+     4:      target += von_mises_notasuffix(1|0,1);
+                       ^
+     5:  }
+   -------------------------------------------------
+
+Only functions with names ending in _lpdf, _lupdf, _lpmf, _lupmf, _cdf, _lcdf, _lccdf can make use of conditional notation.