Fix readFieldText not validating coordinates against screen bounds (#4)

CMakeLists.txt

@@ -51,4 +51,5 @@ if(BUILD_5250SCRIPT_TESTS)
 
     add_5250script_test(test_script_lexer tests/test_script_lexer.cpp)
     add_5250script_test(test_script_parser tests/test_script_parser.cpp)
+    add_5250script_test(test_script_executor_bounds tests/test_script_executor_bounds.cpp)
 endif()

src/script_executor.cpp

@@ -804,6 +804,8 @@ QString ScriptExecutor::readScreenText(int row, int col, int length) const {
 
 QString ScriptExecutor::readFieldText(int row, int col) const {
     if (!m_screen) return {};
+    if (row < 0 || row >= m_screen->rows() || col < 0 || col >= m_screen->cols())
+        return {};
     return m_screen->readFieldText(row, col);
 }
 

tests/test_script_executor_bounds.cpp

@@ -0,0 +1,83 @@
+// 5250ng - A modern IBM TN5250 terminal emulator
+// Copyright (C) 2025-2026 Remi GASCOU (Podalirius)
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+#include <5250script/screen_interface.h>
+#include <5250script/script_executor.h>
+#include <5250script/script_parser.h>
+#include <QSignalSpy>
+#include <QtTest/QtTest>
+
+using namespace core::scripting;
+
+// Fake screen whose readFieldText records the coordinates it receives, so the
+// test can assert that out-of-range coordinates are filtered out by
+// ScriptExecutor before they reach the host screen implementation.
+class RecordingScreen : public ScreenInterface {
+  public:
+    int rows() const override { return 24; }
+    int cols() const override { return 80; }
+    int cursorRow() const override { return 0; }
+    int cursorCol() const override { return 0; }
+    QString readText(int, int, int length) const override { return QString(length, ' '); }
+    QString readFieldText(int row, int col) const override {
+        m_fieldCalls.append(QPoint(row, col));
+        return QStringLiteral("field-content");
+    }
+    KeyboardState keyboardState() const override { return KeyboardState::Unlocked; }
+    bool messageWaiting() const override { return false; }
+
+    mutable QVector<QPoint> m_fieldCalls;
+};
+
+class TestScriptExecutorBounds : public QObject {
+    Q_OBJECT
+  private slots:
+    void readFieldTextFiltersOutOfRangeCoordinates();
+};
+
+// Regression test for #4: EXPECT FIELD AT / EXTRACT FIELD AT with row/col
+// outside the screen dimensions must not reach ScreenInterface::readFieldText.
+void TestScriptExecutorBounds::readFieldTextFiltersOutOfRangeCoordinates() {
+    RecordingScreen screen;
+    ScriptExecutor executor;
+    executor.setScreen(&screen);
+
+    // All three EXTRACTs are out of bounds after the 1-based → 0-based conversion:
+    //   ( 0, 0) -> (-1, -1)      negative row, negative col
+    //   (99,99) -> (98, 98)      row beyond rows(), col beyond cols()
+    //   (1, 99) -> ( 0, 98)      valid row, col beyond cols()
+    // A single in-bounds extract at (1,1) -> (0,0) must still reach the screen.
+    const QString source =
+        "EXTRACT $A FIELD AT 0 0\n"
+        "EXTRACT $B FIELD AT 99 99\n"
+        "EXTRACT $C FIELD AT 1 99\n"
+        "EXTRACT $D FIELD AT 1 1\n";
+
+    ScriptParser parser;
+    auto result = parser.parse(source);
+    QVERIFY(!result.hasErrors());
+
+    QSignalSpy finishedSpy(&executor, &ScriptExecutor::executionFinished);
+    executor.execute(result);
+    QVERIFY(finishedSpy.wait(5000));
+
+    // Only the single in-bounds EXTRACT should have reached the screen.
+    QCOMPARE(screen.m_fieldCalls.size(), 1);
+    QCOMPARE(screen.m_fieldCalls.first(), QPoint(0, 0));
+}
+
+QTEST_MAIN(TestScriptExecutorBounds)
+#include "test_script_executor_bounds.moc"