Fix compiler crash in alternate name suggestion logic (issue ponylang…

…#2508). (ponylang#2552)

* Fix for issue 2508

The pony_assert(ast_id(id == TK_ID) assumes that ast_id(id)) is
always a TK_ID, but that is not the true if the first child of case_ast
is a function or behavior.

This fix checks for a TK_ID for both first and second children of
case_ast and gives up if neither is a TK_ID instead of asserting.

* Add tests for suggest_alt_name

There are three cases tested plus a test for nothing can be suggested.

src/libponyc/pass/refer.c

@@ -222,14 +222,30 @@ static const char* suggest_alt_name(ast_t* ast, const char* name)
   {
     ast_t* id = case_ast;
 
-    if(ast_id(id) != TK_ID)
-      id = ast_child(id);
+    int tk = ast_id(id);
+    if(tk != TK_ID)
+    {
+      AST_GET_CHILDREN(case_ast, first, second);
 
-    pony_assert(ast_id(id) == TK_ID);
-    const char* try_name = ast_name(id);
+      if((tk = ast_id(first)) == TK_ID)
+      {
+        // First is a TK_ID give it as a suggestion
+        id = first;
+      } else if((tk = ast_id(second)) == TK_ID) {
+        // Second is a TK_ID give it as a suggestion
+        id = second;
+      } else {
+        // Giving up on different case as tk != TK_ID
+      }
+    }
 
-    if(ast_get(ast, try_name, NULL) != NULL)
-      return try_name;
+    if(tk == TK_ID)
+    {
+      const char* try_name = ast_name(id);
+
+      if(ast_get(ast, try_name, NULL) != NULL)
+        return try_name;
+    }
   }
 
   // Give up

test/libponyc/suggest_alt_name.cc

@@ -0,0 +1,68 @@
+#include <gtest/gtest.h>
+#include <platform.h>
+
+#include "util.h"
+
+#define TEST_ERRORS(src, err1) \
+  { const char* errs[] = {err1, NULL}; \
+    DO(test_expected_errors(src, "ir", errs)); }
+
+class SuggestAltNameTest : public PassTest
+{};
+
+TEST_F(SuggestAltNameTest, SuggestAltName_Private)
+{
+  const char* src =
+    "actor Main\n"
+    "  var _aStr: String = \"help\"\n"
+
+    "  new create(env: Env) =>\n"
+    "    _aStr = xx()\n"
+
+    "  fun xx(): String =>\n"
+    "    aStr // Undefined suggest _aStr\n";
+
+  TEST_ERRORS(src,
+    "can't find declaration of 'aStr', did you mean '_aStr'?");
+}
+
+TEST_F(SuggestAltNameTest, SuggestAltName_DifferentCaseVariable)
+{
+  const char* src =
+    "actor Main\n"
+    "  var aStr: String = \"help\"\n"
+
+    "  new create(env: Env) =>\n"
+    "    aStr = xx()\n"
+
+    "  fun xx(): String =>\n"
+    "    astr // Undefined, suggest aStr\n";
+
+  TEST_ERRORS(src,
+    "can't find declaration of 'astr', did you mean 'aStr'?");
+}
+
+TEST_F(SuggestAltNameTest, SuggestAltName_DifferentCaseMethod)
+{
+  const char* src =
+    "actor Main\n"
+    "  new create(env: Env) =>\n"
+    "    doit() // Undefined, suggest doIt\n"
+
+    "  fun doIt() =>\n"
+    "    None\n";
+
+  TEST_ERRORS(src,
+    "can't find declaration of 'doit', did you mean 'doIt'?");
+}
+
+TEST_F(SuggestAltNameTest, SuggestAltName_NothingToSuggest)
+{
+  const char* src =
+    "actor Main\n"
+    "  new create(env: Env) =>\n"
+    "    doIt() // Undefined, nothing to suggest\n";
+
+  TEST_ERRORS(src,
+    "can't find declaration of 'doIt'");
+}