Prevent compiler crashes on certain consume expressions

.release-notes/3650.md

@@ -0,0 +1,17 @@
+## Graceful error handling on `consume` expressions
+
+The fix ensures 
+* `consume (consume variable).field` results in a graceful compilation error
+* `consume f().field` results in similar compilation error as `consume f()`
+* Allow `(consume obj).field` expressions
+  The following snippet 
+  ```pony
+	 (consume f).b =  recover Bar end
+  ```
+  must be equivalent to
+
+  ```pony
+     let x = consume f
+	 x.b = recover Bar end
+ ```
+

src/libponyc/pass/refer.c

@@ -139,14 +139,16 @@ static const char* generate_multi_dot_name(ast_t* ast, ast_t** def_found) {
 
     default:
     {
+      if (def == NULL)
+        return stringtab("");
       pony_assert(0);
     }
   }
 
   if(def_found != NULL)
   {
     *def_found = def;
-
+  
     if(def == NULL)
       return stringtab("");
   }
@@ -1166,10 +1168,6 @@ static bool refer_consume(pass_opt_t* opt, ast_t* ast)
             "can't consume a let or embed field");
           return false;
         }
-      } else if (ast_id(left) == TK_CALL) {
-        ast_error(opt->check.errors, ast,
-          "consume expressions must specify a single identifier");
-        return false;
       }
       else
       {

src/libponyc/pass/syntax.c

@@ -696,14 +696,19 @@ static ast_result_t syntax_consume(pass_opt_t* opt, ast_t* ast)
   {
     case TK_THIS:
     case TK_REFERENCE:
-    case TK_DOT:
       return AST_OK;
-
+    case TK_DOT: {
+        AST_GET_CHILDREN(term, left, right);
+        if (ast_id(left) != TK_CALL && ast_id(left) != TK_SEQ) 
+        {
+          return AST_OK;
+        }
+    }
     default: {}
   }
 
   ast_error(opt->check.errors, term,
-    "Consume expressions must specify a single identifier");
+    "Consume expressions must specify an identifier or field");
   return AST_ERROR;
 }
 

test/libponyc/refer.cc

@@ -841,12 +841,62 @@ TEST_F(ReferTest, ConsumeParamVarSubfieldReassignSameExpressionReuse)
 
 TEST_F(ReferTest, ConsumeTupleAccessorOfFunctionValResult)
 {
-    const char* src =
-      "actor Main\n"
-        "new create(env: Env) =>\n"
-          "let a = \"I am a string\"\n"
-          "consume a.chop(1)._1";
-
-    TEST_ERRORS_1(src,
-      "consume expressions must specify a single identifier");
+  const char* src =
+    "actor Main\n"
+      "new create(env: Env) =>\n"
+        "let a = \"I am a string\"\n"
+        "consume a.chop(1)._1";
+
+  TEST_ERRORS_1(src,
+    "Consume expressions must specify an identifier or field");
+}
+
+TEST_F(ReferTest, DoubleConsumeWithFieldAccessor)
+{
+  const char* src = 
+    "class Problem\n"
+      "let _unwrap_me: U8 = 0\n"
+      "fun iso unwrap() =>\n"
+        "let this_iso: Problem iso = consume this\n"
+        "consume (consume this_iso)._unwrap_me";
+
+  TEST_ERRORS_1(src,
+    "Consume expressions must specify an identifier or field");
+}
+
+TEST_F(ReferTest, ConsumeAfterMemberAccessWithConsumeLhs)
+{
+  const char* src =
+    "actor Main\n"
+      "new create(env:Env val) =>\n"
+        "let f : Foo iso = recover Foo end\n"
+        "(consume f).b = recover Bar end\n"
+        "let x:Foo tag = consume f\n"
+    "class Foo\n"
+      "var b: Bar iso\n"
+      "new create() =>\n"
+        "b = recover Bar end\n"
+    "class Bar\n"
+      "new create() => None\n";
+
+    TEST_ERRORS_2(src,
+      "can't use a consumed local or field in an expression",
+      "consume must take 'this', a local, or a parameter");
+}
+
+TEST_F(ReferTest, MemberAccessWithConsumeLhs)
+{
+  const char* src = 
+    "actor Main\n"
+      "new create(env:Env val) =>\n"
+        "let f : Foo iso = recover Foo end\n"
+        "(consume f).b = recover Bar end\n"
+    "class Foo\n"
+      "var b: Bar iso\n"
+        "new create() =>\n"
+          "b = recover Bar end\n"
+    "class Bar\n"
+      "new create() => None\n";
+
+  TEST_COMPILE(src);
 }