identify and handle completing destructuring patterns

Author: zth

analysis/src/CompletionFrontEnd.ml

@@ -572,12 +572,20 @@ let completionWithParser1 ~currentFile ~debug ~offset ~path ~posCursor ~text =
   in
   let structure_item (iterator : Ast_iterator.iterator)
       (item : Parsetree.structure_item) =
+    unsetLookingForPat;
     let processed = ref false in
     (match item.pstr_desc with
     | Pstr_open {popen_lid} ->
       scope := !scope |> Scope.addOpen ~lid:popen_lid.txt
     | Pstr_primitive vd -> scopeValueDescription vd
     | Pstr_value (recFlag, bindings) ->
+      (* Identify relevant destructures for completion, like `let {<com>} = someVar` or `let (true, false) = someFn()`. *)
+      (match bindings with
+      | [{pvb_pat = {ppat_desc = Ppat_record _ | Ppat_tuple _}; pvb_expr}] -> (
+        match exprToContextPath pvb_expr with
+        | None -> ()
+        | Some ctxPath -> setLookingForPat ctxPath)
+      | _ -> ());
       if recFlag = Recursive then bindings |> List.iter scopeValueBinding;
       bindings |> List.iter (fun vb -> iterator.value_binding iterator vb);
       if recFlag = Nonrecursive then bindings |> List.iter scopeValueBinding;

analysis/tests/src/CompletionPattern.res

@@ -72,3 +72,6 @@ let _ = switch f {
   nest.nested
 | _ => false
 }
+
+// let {} = f
+//      ^com

analysis/tests/src/expected/CompletionPattern.res.txt

@@ -214,3 +214,33 @@ Completable: Cpattern Value[nest]->recordBody
     "documentation": null
   }]
 
+Complete src/CompletionPattern.res 75:8
+looking for: Cpath Value[f] 
+posCursor:[75:8] posNoWhite:[75:7] Found pattern:[75:7->75:9]
+Completable: Cpattern Value[f]->recordBody
+[{
+    "label": "first",
+    "kind": 5,
+    "tags": [],
+    "detail": "first: int\n\nsomeRecord",
+    "documentation": null
+  }, {
+    "label": "second",
+    "kind": 5,
+    "tags": [],
+    "detail": "second: (bool, option<someRecord>)\n\nsomeRecord",
+    "documentation": null
+  }, {
+    "label": "optThird",
+    "kind": 5,
+    "tags": [],
+    "detail": "optThird: option<[#second(someRecord) | #first]>\n\nsomeRecord",
+    "documentation": null
+  }, {
+    "label": "nest",
+    "kind": 5,
+    "tags": [],
+    "detail": "nest: nestedRecord\n\nsomeRecord",
+    "documentation": null
+  }]
+