feat: Augment schema parser error messages

src/fdb5/CMakeLists.txt

@@ -23,6 +23,8 @@ list( APPEND fdb5_srcs
     api/FDBFactory.h
     api/FDBStats.cc
     api/FDBStats.h
+    api/exceptions/SchemaError.cc
+    api/exceptions/SchemaError.h
     api/LocalFDB.cc
     api/LocalFDB.h
     api/RandomFDB.cc

src/fdb5/api/exceptions/SchemaError.cc

@@ -0,0 +1,18 @@
+/*
+ * (C) Copyright 2026- ECMWF.
+ *
+ * This software is licensed under the terms of the Apache Licence Version 2.0
+ * which can be obtained at http://www.apache.org/licenses/LICENSE-2.0.
+ * In applying this licence, ECMWF does not waive the privileges and immunities
+ * granted to it by virtue of its status as an intergovernmental organisation nor
+ * does it submit to any jurisdiction.
+ */
+
+#include "fdb5/api/exceptions/SchemaError.h"
+
+namespace fdb5 {
+
+SchemaError::SchemaError(const std::string& path, const std::string& what, size_t line) :
+    eckit::StreamParser::Error(path + ": " + what, line) {}
+
+}  // namespace fdb5

src/fdb5/api/exceptions/SchemaError.h

@@ -0,0 +1,26 @@
+/*
+ * (C) Copyright 2026- ECMWF.
+ *
+ * This software is licensed under the terms of the Apache Licence Version 2.0
+ * which can be obtained at http://www.apache.org/licenses/LICENSE-2.0.
+ * In applying this licence, ECMWF does not waive the privileges and immunities
+ * granted to it by virtue of its status as an intergovernmental organisation nor
+ * does it submit to any jurisdiction.
+ */
+
+#pragma once
+
+#include <cstddef>
+#include <string>
+
+#include "eckit/parser/StreamParser.h"
+
+namespace fdb5 {
+
+class SchemaError : public eckit::StreamParser::Error {
+public:
+
+    SchemaError(const std::string& path, const std::string& what, size_t line = 0);
+};
+
+}  // namespace fdb5

src/fdb5/rules/Schema.cc

@@ -9,12 +9,9 @@
  */
 
 #include <cstddef>
-#include <fstream>
-#include <iostream>
 #include <memory>
 #include <mutex>
 #include <optional>
-#include <set>
 #include <sstream>
 #include <string>
 #include <tuple>
@@ -27,6 +24,7 @@
 #include "eckit/utils/Tokenizer.h"
 
 #include "fdb5/LibFdb5.h"
+#include "fdb5/api/exceptions/SchemaError.h"
 #include "fdb5/database/Key.h"
 #include "fdb5/database/WriteVisitor.h"
 #include "fdb5/rules/Predicate.h"
@@ -190,23 +188,28 @@ void Schema::load(const eckit::PathName& path, const bool replace) {
 
     LOG_DEBUG_LIB(LibFdb5) << "Loading FDB rules from " << path << std::endl;
 
-    std::ifstream in(path.localPath());
-    if (!in) {
-        auto ex = eckit::CantOpenFile(path);
-        ex.dumpStackTrace();
-        throw ex;
+    // Constructing the parser opens `path`, so a missing file is reported
+    // (as eckit::CantOpenFile) before any existing rules are cleared.
+    SchemaParser parser(path);
+
+    if (replace) {
+        clear();
     }
 
-    load(in, replace);
+    parser.parse(rules_, registry_);
+
+    check();
 }
 
 void Schema::load(std::istream& s, const bool replace) {
 
+    SchemaParser parser(s);
+
     if (replace) {
         clear();
     }
 
-    SchemaParser(s).parse(rules_, registry_);
+    parser.parse(rules_, registry_);
 
     check();
 }