CTest: add safe conversion from cmDuration to integer types

A problem area by recent refactoring of time to std::chrono has been the
unsafe conversion from duration<double> to std::chrono::seconds, which
is of an unspecified integer type.

This commit adds a template function that for a given type provides a
safe conversion, effectively clamping a duration<double> into what fits
safely in that type. A specialisation for int and unsigned int are
provided.

It changes the protential problem areas to use this safe function.

1 files changed, 27 insertions, 0 deletions

diff --git a/Source/cmDuration.cxx b/Source/cmDuration.cxx
new file mode 100644
index 0000000..8ca5d8d
--- /dev/null
+++ b/Source/cmDuration.cxx
@@ -0,0 +1,27 @@
+/* Distributed under the OSI-approved BSD 3-Clause License.  See accompanying
+   file Copyright.txt or https://cmake.org/licensing for details.  */
+#define CMDURATION_CPP
+#include "cmDuration.h"
+
+template <typename T>
+T cmDurationTo(const cmDuration& duration)
+{
+  /* This works because the comparison operators for duration rely on
+   * std::common_type.
+   * So for example duration<int>::max() gets promoted to a duration<double>,
+   * which can then be safely compared.
+   */
+  if (duration >= std::chrono::duration<T>::max()) {
+    return std::chrono::duration<T>::max().count();
+  }
+  if (duration <= std::chrono::duration<T>::min()) {
+    return std::chrono::duration<T>::min().count();
+  }
+  // Ensure number of seconds by defining ratio<1>
+  return std::chrono::duration_cast<std::chrono::duration<T, std::ratio<1>>>(
+           duration)
+    .count();
+}
+
+template int cmDurationTo<int>(const cmDuration&);
+template unsigned int cmDurationTo<unsigned int>(const cmDuration&);