Add flag to print compiler's over-approximation of factor graph

src/driver/Entry.ml

@@ -90,6 +90,9 @@ let stan2cpp model_name model (flags : Flags.t) (output : other_output -> unit)
     output (Warnings (Pedantic_analysis.warn_uninitialized mir));
   if flags.warn_pedantic then
     output (Warnings (Pedantic_analysis.warn_pedantic mir));
+  if flags.debug_settings.debug_print_factor_graph then
+    print_endline
+      (Factor_graph.factor_graph_to_dot (Factor_graph.prog_factor_graph mir));
   debug_output_mir output mir flags.debug_settings.print_mir;
   let* generation_context =
     match flags.debug_settings.debug_data_json with

src/driver/Flags.ml

@@ -28,7 +28,8 @@ and debug_settings =
   ; print_lir: bool
   ; debug_generate_data: bool
   ; debug_generate_inits: bool
-  ; debug_data_json: (string * string) option }
+  ; debug_data_json: (string * string) option
+  ; debug_print_factor_graph: bool }
 
 and debug_options = Off | Basic | Pretty
 
@@ -63,7 +64,8 @@ let default =
       ; print_lir= false
       ; debug_generate_data= false
       ; debug_generate_inits= false
-      ; debug_data_json= None }
+      ; debug_data_json= None
+      ; debug_print_factor_graph= false }
   ; line_length= 78
   ; canonicalizer_settings= Frontend.Canonicalize.none
   ; warn_pedantic= false

src/driver/Flags.mli

@@ -39,7 +39,8 @@ and debug_settings =
   ; print_lir: bool
   ; debug_generate_data: bool
   ; debug_generate_inits: bool
-  ; debug_data_json: (string * string) option }
+  ; debug_data_json: (string * string) option
+  ; debug_print_factor_graph: bool }
 
 and debug_options = Off | Basic | Pretty
 

src/stanc/CLI.ml

@@ -321,6 +321,12 @@ module Debug_Options = struct
        it." in
     debug_basic_or_pretty ~doc "debug-transformed-mir"
 
+  let debug_print_factor_graph =
+    let doc =
+      "For debugging purposes: print a conservative over-approximation of the \
+       factor graph for the model(s) implemented in the Stan program." in
+    Arg.(value & flag & info ["debug-print-factor-graph"] ~doc ~docs)
+
   let force_soa =
     let doc =
       "Debugging features. Valid values: $(b,-fsoa) to force on the Struct of \
@@ -370,7 +376,8 @@ module Conversion = struct
     and+ print_lir = debug_lir
     and+ debug_generate_data
     and+ debug_generate_inits
-    and+ debug_data_json = Term.ret debug_data_json in
+    and+ debug_data_json = Term.ret debug_data_json
+    and+ debug_print_factor_graph in
     Driver.Flags.
       { print_ast
       ; print_typed_ast
@@ -382,7 +389,8 @@ module Conversion = struct
       ; print_lir
       ; debug_generate_data
       ; debug_generate_inits
-      ; debug_data_json }
+      ; debug_data_json
+      ; debug_print_factor_graph }
 
   let flags : Driver.Flags.t Term.t =
     let open Options in

src/stancjs/conversion.ml

@@ -131,6 +131,7 @@ let process_flags name code (flags : 'a Js.opt) includes :
               ; print_mem_patterns= is_flag_set "debug-mem-patterns"
               ; force_soa= None
               ; print_lir= is_flag_set "debug-lir"
+              ; debug_print_factor_graph= is_flag_set "debug-print-factor-graph"
               ; debug_generate_data= is_flag_set "debug-generate-data"
               ; debug_generate_inits= is_flag_set "debug-generate-inits"
               ; debug_data_json=

test/integration/cli-args/debug-flags.t/run.t

@@ -577,6 +577,17 @@ Flags not used elsewhere in the tests
     parameters real theta; //real
   }
 
+  $ stanc basic.stan --debug-print-factor-graph
+  graph {
+  "bernoulli_lupmf(y, theta)" [shape=box]
+  "beta_lupdf(theta, promote(1, real, data), promote(1, real, data))" [shape=box]
+  theta
+  y
+  "bernoulli_lupmf(y, theta)" -- theta
+  "bernoulli_lupmf(y, theta)" -- y
+  "beta_lupdf(theta, promote(1, real, data), promote(1, real, data))" -- theta
+  }
+
   $ stanc parse_error.stan --debug-parse
   Syntax error in 'parse_error.stan', line 1, column 0 to column 5, parsing error:
      -------------------------------------------------

test/integration/cli-args/stanc.t

@@ -178,6 +178,10 @@ Show help
          --debug-parse
              For debugging purposes: print the parser actions.
 
+         --debug-print-factor-graph
+             For debugging purposes: print a conservative over-approximation of
+             the factor graph for the model(s) implemented in the Stan program.
+
          --debug-transformed-mir
              For debugging purposes: print the MIR after the backend has
              transformed it.