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+CMP0115
+-------
+
+.. versionadded:: 3.20
+
+Source file extensions must be explicit.
+
+In CMake 3.19 and below, if a source file could not be found by the name
+specified, it would append a list of known extensions to the name to see if
+the file with the extension could be found. For example, this would allow the
+user to run:
+
+.. code-block:: cmake
+
+  add_executable(exe main)
+
+and put ``main.c`` in the executable without specifying the extension.
+
+Starting in CMake 3.20, CMake prefers all source files to have their extensions
+explicitly listed:
+
+.. code-block:: cmake
+
+  add_executable(exe main.c)
+
+The ``OLD`` behavior for this policy is to implicitly append known extensions
+to source files if they can't be found. The ``NEW`` behavior of this policy is
+to not append known extensions and require them to be explicit.
+
+This policy was introduced in CMake version 3.20.  CMake version |release|
+warns when the policy is not set and uses ``OLD`` behavior. Use the
+:command:`cmake_policy` command to set it to ``OLD`` or ``NEW`` explicitly.
+
+.. include:: DEPRECATED.txt