Update the workaround for restore_cache on macOS not to delete files completely

.circleci/config.yml

@@ -160,16 +160,34 @@ defaults:
         - store_test_results: *store_test_results
         - store_artifacts: *artifacts_test_results
 
-  - steps_restore_cache_homebrew_workaround: &steps_restore_cache_homebrew_workaround
+  - steps_homebrew_workaround_before_restore_cache: &steps_homebrew_workaround_before_restore_cache
       steps:
         - run:
-            # FIXME: For some reason restore_cache fails saying that it cannot remove the scm/ dir.
-            # The directory contains only two files: `git` (wrapper script over git) and `svn` (symlink
-            # to `git`). This looks like a bug in restore_cache. Removing scm/ is a workaround.
+            # Homebrew has recently replaced one of its dirs with a symlink to another.
+            # This makes tar used by restore_cache fail - the image contains an older version of
+            # Homebrew installed where it's a directory and tar refuses to overwrite a dir with a link.
+            # Removing the directory manually is a workaround that works only in case we do have
+            # cached files to restore. If we don't, we still need this dir because it contains
+            # a git wrapper that Homebrew uses to update itself. The solution is to just rename the
+            # dir before restore_cache and renamed it back afterwards.
             # See https://github.com/ethereum/solidity/pull/12106 for more details.
             name: Workaround for restore_cache + /usr/local/Homebrew/Library/Homebrew/shims/scm/
             command: |
-              rm -r /usr/local/Homebrew/Library/Homebrew/shims/scm/
+              cd /usr/local/Homebrew/Library/Homebrew/shims/
+              mv scm/ scm-backup/
+
+  - steps_homebrew_workaround_after_restore_cache: &steps_homebrew_workaround_after_restore_cache
+      steps:
+        - run:
+            name: Workaround for restore_cache + /usr/local/Homebrew/Library/Homebrew/shims/scm/
+            command: |
+              cd /usr/local/Homebrew/Library/Homebrew/shims/
+              if ! [[ -e scm/ ]]
+              then
+                mv scm-backup/ scm/
+              else
+                rm -r scm-backup/
+              fi
 
   - test_ubuntu1604_clang: &test_ubuntu1604_clang
       docker:
@@ -638,12 +656,17 @@ jobs:
       - checkout
       - when:
           condition: true
-          <<: *steps_restore_cache_homebrew_workaround
+          # FIXME: Remove this workaround when CircleCI fixes restore_cache.
+          <<: *steps_homebrew_workaround_before_restore_cache
       - restore_cache:
           keys:
             - dependencies-osx-{{ arch }}-{{ checksum ".circleci/osx_install_dependencies.sh" }}
       # DO NOT EDIT between here and save_cache, but rather edit ./circleci/osx_install_dependencies.sh
       # WARNING! If you do edit anything here instead, remember to invalidate the cache manually.
+      - when:
+          condition: true
+          # FIXME: Remove this workaround when CircleCI fixes restore_cache.
+          <<: *steps_homebrew_workaround_after_restore_cache
       - run:
           name: Install build dependencies
           command: ./.circleci/osx_install_dependencies.sh
@@ -677,10 +700,15 @@ jobs:
       - checkout
       - when:
           condition: true
-          <<: *steps_restore_cache_homebrew_workaround
+          # FIXME: Remove this workaround when CircleCI fixes restore_cache.
+          <<: *steps_homebrew_workaround_before_restore_cache
       - restore_cache:
           keys:
             - dependencies-osx-{{ arch }}-{{ checksum ".circleci/osx_install_dependencies.sh" }}
+      - when:
+          condition: true
+          # FIXME: Remove this workaround when CircleCI fixes restore_cache.
+          <<: *steps_homebrew_workaround_after_restore_cache
       - attach_workspace:
           at: .
       - run: *run_soltest
@@ -696,10 +724,15 @@ jobs:
       - checkout
       - when:
           condition: true
-          <<: *steps_restore_cache_homebrew_workaround
+          # FIXME: Remove this workaround when CircleCI fixes restore_cache.
+          <<: *steps_homebrew_workaround_before_restore_cache
       - restore_cache:
           keys:
             - dependencies-osx-{{ arch }}-{{ checksum ".circleci/osx_install_dependencies.sh" }}
+      - when:
+          condition: true
+          # FIXME: Remove this workaround when CircleCI fixes restore_cache.
+          <<: *steps_homebrew_workaround_after_restore_cache
       - attach_workspace:
           at: .
       - run: *run_cmdline_tests