Add explicit test for file not found

...caching the metadata moved where ParquetTable did I/O,
which introduced a segfault on not found

parquet/parquet.cc

@@ -80,27 +80,26 @@ static int parquetConnect(
   // Remove the delimiting single quotes
   std::string fname = argv[3];
   fname = fname.substr(1, fname.length() - 2);
-  std::unique_ptr<ParquetTable> table(new ParquetTable(fname));
-
   std::unique_ptr<sqlite3_vtab_parquet, void(*)(void*)> vtab(
       (sqlite3_vtab_parquet*)sqlite3_malloc(sizeof(sqlite3_vtab_parquet)),
       sqlite3_free);
   memset(vtab.get(), 0, sizeof(*vtab.get()));
 
   try {
+    std::unique_ptr<ParquetTable> table(new ParquetTable(fname));
+
     std::string create = table->CreateStatement();
     int rc = sqlite3_declare_vtab(db, create.data());
     if(rc)
       return rc;
 
+    vtab->table = table.release();
+    *ppVtab = (sqlite3_vtab*)vtab.release();
+    return SQLITE_OK;
   } catch (const std::exception& e) {
     *pzErr = sqlite3_mprintf(e.what());
     return SQLITE_ERROR;
   }
-
-  vtab->table = table.release();
-  *ppVtab = (sqlite3_vtab*)vtab.release();
-  return SQLITE_OK;
 }
 
 /*

tests/test-all

@@ -4,6 +4,7 @@ set -euo pipefail
 here=$(dirname "${BASH_SOURCE[0]}")
 
 set -x
+"$here"/test-non-existent
 "$here"/test-unsupported
 "$here"/test-supported
 "$here"/test-queries

tests/test-non-existent

@@ -0,0 +1,33 @@
+#!/bin/bash
+set -euo pipefail
+
+# Verify that loading a non existent file is an error, not a segfault
+
+load_nonexistent() {
+  cat <<EOF
+.echo on
+.load parquet/libparquet
+.testcase notfound
+.bail on
+CREATE VIRTUAL TABLE test USING parquet('$root/doesnotexist.parquet');
+SELECT 123;
+EOF
+}
+
+
+main() {
+  root=$(dirname "${BASH_SOURCE[0]}")/..
+  root=$(readlink -f "$root")
+  cd "$root"
+
+  #This line will exit with non-zero in case of a segfault.
+  "$root"/sqlite/sqlite3 -init <(load_nonexistent) < /dev/null > /dev/null 2> testcase-stderr.txt
+
+  # We expect the 'SELECT 123' command to NOT have been run
+  if grep -q 123 testcase-out.txt; then
+    echo "...FAILED; expected an error message. Check testcase-{out,err}.txt" >&2
+    exit 1
+  fi
+}
+
+main "$@"