Limit tab completion to text before the cursor

`substr` takes a count, so the text after the cursor joined the prefix.

test/Makefile.am

@@ -69,6 +69,8 @@ rtorrent_Test_Src_SOURCES = $(rtorrent_Test_Common) \
 	src/test_command_string.h \
 	src/test_command_throttle.cc \
 	src/test_command_throttle.h \
+	src/test_input_path_input.cc \
+	src/test_input_path_input.h \
 	src/test_session_commit.cc \
 	src/test_session_commit.h \
 	src/test_session_storer.cc \

test/src/test_input_path_input.cc

@@ -0,0 +1,77 @@
+#include "config.h"
+
+#include "test/src/test_input_path_input.h"
+
+#include <cstdlib>
+#include <sys/stat.h>
+#include <unistd.h>
+
+#include "input/path_input.h"
+
+CPPUNIT_TEST_SUITE_REGISTRATION(TestInputPathInput);
+
+void
+TestInputPathInput::setUp() {
+  test_fixture::setUp();
+
+  char temp_dir[] = "/tmp/rtorrent_test_path_input_XXXXXX";
+
+  CPPUNIT_ASSERT(mkdtemp(temp_dir) != nullptr);
+
+  m_temp_dir = temp_dir;
+
+  CPPUNIT_ASSERT_EQUAL(0, mkdir((m_temp_dir + "/alpha").c_str(), 0755));
+  CPPUNIT_ASSERT_EQUAL(0, mkdir((m_temp_dir + "/alpha/beta").c_str(), 0755));
+}
+
+void
+TestInputPathInput::tearDown() {
+  rmdir((m_temp_dir + "/alpha/beta").c_str());
+  rmdir((m_temp_dir + "/alpha").c_str());
+  rmdir(m_temp_dir.c_str());
+
+  test_fixture::tearDown();
+}
+
+// Tab at the end of the line completes the trailing component.
+void
+TestInputPathInput::test_complete_at_end() {
+  input::PathInput input;
+
+  input.str() = m_temp_dir + "/al";
+  input.set_pos(input.str().size());
+
+  CPPUNIT_ASSERT(input.pressed('\t'));
+
+  CPPUNIT_ASSERT_EQUAL(m_temp_dir + "/alpha/", input.str());
+  CPPUNIT_ASSERT_EQUAL(input.str().size(), input.get_pos());
+}
+
+// The same completion with the cursor left inside the line. Only the text up to
+// the cursor selects the entry, and the rest of the line is discarded.
+void
+TestInputPathInput::test_complete_mid_line() {
+  input::PathInput input;
+
+  input.str() = m_temp_dir + "/alZZZ";
+  input.set_pos(m_temp_dir.size() + 3);
+
+  CPPUNIT_ASSERT(input.pressed('\t'));
+
+  CPPUNIT_ASSERT_EQUAL(m_temp_dir + "/alpha/", input.str());
+  CPPUNIT_ASSERT_EQUAL(input.str().size(), input.get_pos());
+}
+
+// A cursor resting on a separator keeps completing the component after it.
+void
+TestInputPathInput::test_cursor_on_separator() {
+  input::PathInput input;
+
+  input.str() = m_temp_dir + "/alpha/be";
+  input.set_pos(m_temp_dir.size() + 6);
+
+  CPPUNIT_ASSERT(input.pressed('\t'));
+
+  CPPUNIT_ASSERT_EQUAL(m_temp_dir + "/alpha/beta/", input.str());
+  CPPUNIT_ASSERT_EQUAL(input.str().size(), input.get_pos());
+}

test/src/test_input_path_input.h

@@ -0,0 +1,24 @@
+#include "test/helpers/test_fixture.h"
+
+#include <string>
+
+class TestInputPathInput : public test_fixture {
+  CPPUNIT_TEST_SUITE(TestInputPathInput);
+
+  CPPUNIT_TEST(test_complete_at_end);
+  CPPUNIT_TEST(test_complete_mid_line);
+  CPPUNIT_TEST(test_cursor_on_separator);
+
+  CPPUNIT_TEST_SUITE_END();
+
+public:
+  void setUp();
+  void tearDown();
+
+  void test_complete_at_end();
+  void test_complete_mid_line();
+  void test_cursor_on_separator();
+
+private:
+  std::string m_temp_dir;
+};