[textual] Improve generated ProcDesc.Node locations

Summary:
This diff uses min instr line for node's loc. This makes node placement in a debug HTML a bit more
predictable and relevant compared to using block labels' locations which can be more detached from
the actual source code when we're dealing with translated sources (e.g. Hack->Textual).

Note that a single node can still accumulate instructions from a large number of lines (e.g. a scope
of 20 lines in the source file). Ideally, we'd improve the way we generate blocks (perhaps split
blocks into more manageable chunks) to reduce the scope of each particular node.

Reviewed By: geralt-encore

Differential Revision: D46234875

fbshipit-source-id: a895c238b3db6f8c92fc5ab36756b2dfc64cbb82

infer/src/textual/TextualSil.ml

@@ -756,7 +756,19 @@ module NodeBridge = struct
     let last_loc = LocationBridge.to_sil sourcefile node.last_loc in
     let last = TerminatorBridge.to_sil lang decls_env procname pdesc last_loc node.last in
     let instrs = Option.value_map ~default:instrs ~f:(fun instr -> instrs @ [instr]) last in
-    let loc = LocationBridge.to_sil sourcefile node.label_loc in
+    (* Use min instr line for node's loc. This makes node placement in a debug HTML a bit more
+       predictable and relevant compared to using block labels' locations which can be more detached
+       from the actual source code when we're dealing with translated sources
+       (e.g. Hack->Textual). *)
+    let loc =
+      let known_instr_lines =
+        List.filter_map instrs ~f:(fun instr ->
+            match (Sil.location_of_instr instr).line with -1 -> None | other -> Some other )
+      in
+      let label_loc = LocationBridge.to_sil sourcefile node.label_loc in
+      let first_line = List.fold known_instr_lines ~init:label_loc.line ~f:min in
+      {label_loc with line= first_line}
+    in
     let nkind = SilProcdesc.Node.Stmt_node MethodBody in
     SilProcdesc.create_node pdesc loc nkind instrs