Implement #624: Use shorter hashes with CPM_SOURCE_CACHE (#631)

* Add ASSERT_CONTENTS_EQUAL test macro in testing.cmake

Checks if the contents of a file matches the given input

* Use shorter hashes with CPM_SOURCE_CACHE (#624)

Uses shorter hashes with CPM_SOURCE_CACHE. Falls back to a longer hash
if necessary (ie, if there's a collision with an existing hash).

See: https://github.com/cpm-cmake/CPM.cmake/issues/624

* Update integration tests to support shorter hashes

* trigger ci

* run cmake-format

* if already available, use the legacy cache hash

* create temporary file in current binary dir

* add test case for legacy hash

---------

Co-authored-by: Lars Melchior <lars.melchior@gmail.com>
Co-authored-by: Lars Melchior <TheLartians@users.noreply.github.com>

test/integration/test_source_cache.rb

@@ -75,6 +75,17 @@ class SourceCache < IntegrationTest
     assert_equal ver, package.ver
     expected_parent_dir = File.join(@cache_dir, name.downcase)
     assert package.src_dir.start_with?(expected_parent_dir), "#{package.src_dir} must be in #{expected_parent_dir}"
-    assert_equal dir_sha1, File.basename(package.src_dir)
+
+    # The hash has been shortened by cpm_get_shortest_hash. The following
+    # should hold:
+    # - The short hash should be a prefix of the input hash
+    # - There should be a file ".../${short_hash}.hash" which matches the full hash
+    short_hash = File.basename(package.src_dir)
+    assert dir_sha1.start_with?(short_hash), "short_hash should be a prefix of dir_sha1"
+
+    # Check that the full hash is stored in the .hash file
+    hash_file = "#{package.src_dir}.hash"
+    assert File.exist?(hash_file), "Hash file #{hash_file} should exist"
+    assert_equal dir_sha1, File.read(hash_file), "Hash file should contain the full original hash"
   end
 end