Error tolerance for functional args -- patching funs

Summary:
Ill-typed functional arguments are sometimes never patched, making error tolerance loop indefinitely.
This is because the reported erroneous expr can be a variable introduced by eta-expansion, thus it will never match a patchable expression.

This diff introduces a heuristic to detect such cases and then patches the functional argument.

Reviewed By: ilya-klyuchnikov

Differential Revision: D43187017

fbshipit-source-id: 3741eaf59f0770922652a769d776eb7736ab00cb

Author: VLanvin

eqwalizer/src/main/scala/com/whatsapp/eqwalizer/ast/Patch.scala

@@ -84,6 +84,11 @@ class Patch(erroneousExpr: Expr) {
           ReqMapUpdate(patchExpr(map), kvs.map(patchAtomicKV))(e.pos)
         case u @ GenMapUpdate(map, kvs) =>
           GenMapUpdate(patchExpr(map), kvs.map(patchKV))(e.pos, u.approximated)
+        // The erroneous expr may be a variable introduced by eta-expansion of a functional argument,
+        // in which case e == erroneousExpr will never match and the expr will not be patched.
+        // The case below is a good enough heuristic to detect such cases.
+        case _: LocalFun | _: RemoteFun if erroneousExpr.pos == e.pos && erroneousExpr.isInstanceOf[Var] =>
+          dynamicCast(e)
         case _: Var | _: AtomLit | _: IntLit | FloatLit() | StringLit(_) | NilLit() | _: LocalFun | _: RemoteFun |
             _: DynRemoteFun | _: DynRemoteFunArity | _: RecordIndex =>
           e

eqwalizer/test_projects/_cli/stats.json

@@ -27,7 +27,7 @@
     "fixme_count": 7,
     "is_generated": false,
     "eqwalizer_enabled": true,
-    "error_count": 101,
+    "error_count": 97,
     "is_test": false,
     "type_dependencies": [
       "misc"

eqwalizer/test_projects/fault_tolerance/src/fault_tolerance.erl.check

@@ -577,19 +577,3 @@ apply_map(L) ->                            | ERROR   |
     map_pair(L, fun make_pair/2).          |         | Arg 2 of 'make_pair/2'.
                                            |         | Expected: number()
                                            |         | Got     : term()
-                                           |         | ---
-                                           |         | Arg 2 of 'make_pair/2'.
-                                           |         | Expected: number()
-                                           |         | Got     : term()
-                                           |         | ---
-                                           |         | Arg 2 of 'make_pair/2'.
-                                           |         | Expected: number()
-                                           |         | Got     : term()
-                                           |         | ---
-                                           |         | Arg 2 of 'make_pair/2'.
-                                           |         | Expected: number()
-                                           |         | Got     : term()
-                                           |         | ---
-                                           |         | Arg 2 of 'make_pair/2'.
-                                           |         | Expected: number()
-                                           |         | Got     : term()

eqwalizer/test_projects/fault_tolerance/src/fault_tolerance.erl.json

@@ -1152,54 +1152,6 @@
       "expressionOrNull": null,
       "explanationOrNull": null
     },
-    {
-      "range": {
-        "start": 5291,
-        "end": 5306
-      },
-      "lineAndCol": null,
-      "message": "Expected: number()\nGot     : term()",
-      "uri": "https://fb.me/eqwalizer_errors#expected_subtype",
-      "code": "expected_subtype",
-      "expressionOrNull": "Arg 2 of 'make_pair/2'",
-      "explanationOrNull": null
-    },
-    {
-      "range": {
-        "start": 5291,
-        "end": 5306
-      },
-      "lineAndCol": null,
-      "message": "Expected: number()\nGot     : term()",
-      "uri": "https://fb.me/eqwalizer_errors#expected_subtype",
-      "code": "expected_subtype",
-      "expressionOrNull": "Arg 2 of 'make_pair/2'",
-      "explanationOrNull": null
-    },
-    {
-      "range": {
-        "start": 5291,
-        "end": 5306
-      },
-      "lineAndCol": null,
-      "message": "Expected: number()\nGot     : term()",
-      "uri": "https://fb.me/eqwalizer_errors#expected_subtype",
-      "code": "expected_subtype",
-      "expressionOrNull": "Arg 2 of 'make_pair/2'",
-      "explanationOrNull": null
-    },
-    {
-      "range": {
-        "start": 5291,
-        "end": 5306
-      },
-      "lineAndCol": null,
-      "message": "Expected: number()\nGot     : term()",
-      "uri": "https://fb.me/eqwalizer_errors#expected_subtype",
-      "code": "expected_subtype",
-      "expressionOrNull": "Arg 2 of 'make_pair/2'",
-      "explanationOrNull": null
-    },
     {
       "range": {
         "start": 5291,