add_files_to_view: flip incorrect default (#29700)

lib/spack/spack/build_systems/python.py

@@ -216,7 +216,7 @@ def view_file_conflicts(self, view, merge_map):
 
         return conflicts
 
-    def add_files_to_view(self, view, merge_map, skip_if_exists=False):
+    def add_files_to_view(self, view, merge_map, skip_if_exists=True):
         bin_dir = self.spec.prefix.bin
         python_prefix = self.extendee_spec.prefix
         python_is_external = self.extendee_spec.external

lib/spack/spack/filesystem_view.py

@@ -810,7 +810,7 @@ def skip_list(file):
                 full_src = os.path.join(src_root, src_rel)
                 full_dst = os.path.join(self._root, dst_rel)
                 merge_map[full_src] = full_dst
-            spec.package.add_files_to_view(self, merge_map, skip_if_exists=True)
+            spec.package.add_files_to_view(self, merge_map, skip_if_exists=False)
 
         # Finally create the metadata dirs.
         self.link_metadata(specs)

lib/spack/spack/package.py

@@ -479,7 +479,7 @@ def view_file_conflicts(self, view, merge_map):
         """
         return set(dst for dst in merge_map.values() if os.path.lexists(dst))
 
-    def add_files_to_view(self, view, merge_map, skip_if_exists=False):
+    def add_files_to_view(self, view, merge_map, skip_if_exists=True):
         """Given a map of package files to destination paths in the view, add
         the files to the view. By default this adds all files. Alternative
         implementations may skip some files, for example if other packages