Update: tree-shaking test for external function case

Author: LKedward

example_packages/tree_shake/app/say_Hello.f90

@@ -3,5 +3,13 @@ program say_Hello
 
     implicit none
 
+    interface
+        function external_function() result(i)
+            integer :: i
+        end function external_function
+    end interface
+
     print *, make_greeting("World")
+    print *, external_function()
+
 end program say_Hello

example_packages/tree_shake/src/extra_m.f90

@@ -0,0 +1,15 @@
+! This module is not used by any other sources, 
+!  however because it also contains an external function
+!  it cannot be dropped during tree-shaking/pruning 
+module extra_m
+    use subdir_constants, only: FAREWELL_STR
+    implicit none
+    private
+
+    integer, parameter :: m = 0
+end
+
+function external_function() result(i)
+    integer :: i
+    i = 1
+end function external_function

example_packages/tree_shake/src/farewell_m.f90

@@ -1,3 +1,6 @@
+! This module is not used by any other sources
+!  and only contains a module (no non-module subprograms),
+!  therefore it should be dropped during tree-shaking/pruning
 module farewell_m
     use subdir_constants, only: FAREWELL_STR
     implicit none

example_packages/tree_shake/src/greet_m.f90

@@ -1,3 +1,5 @@
+! This module is directly by the executables and
+!  hence should not be dropped during tree-shaking/pruning
 module greet_m
     use subdir_constants, only: GREET_STR
     implicit none

example_packages/tree_shake/src/subdir/constants.f90

@@ -1,3 +1,5 @@
+! This module is used indirectly by the executables
+!  and hence should not be dropped during tree-shaking/pruning
 module subdir_constants
 implicit none