Auto merge of #5954 - ajwann:check-permissions-for-client-index-dir, r=segiddins

ensure $HOME and Dir.tmpdir are writable

Fixes #5518

### What was the end-user problem that led to this PR?
A user had issues installing gems due to a permissions issue on the temp dir, because
Bundler was not checking for proper permissions on the temp directory or $HOME.

### What was your diagnosis of the problem?
After discussing the issue with @colby-swandale, the solution was to check permissions on $HOME and the ```tmpdir```.

### What is your fix for the problem, implemented in this PR?
The creation of the [temp dir](https://github.com/bundler/bundler/blob/master/lib/bundler/compact_index_client/updater.rb#L31) is now wrapped in the block passed to ```filesystem_access```, so ```filesystem_access``` will rescue the ```Errno::EACCES``` exception which is thrown if the effective user of the bundler process doesn't have sufficient permissions to create the temp dir.

### Why did you choose this fix out of the possible options?
I chose this fix because it's what was discussed in the original issue thread.

2 files changed, 19 insertions, 0 deletions

diff --git a/lib/bundler/compact_index_client/updater.rb b/lib/bundler/compact_index_client/updater.rb
index 6a66fbc3fe..e80574e3ba 100644
--- a/lib/bundler/compact_index_client/updater.rb
+++ b/lib/bundler/compact_index_client/updater.rb
@@ -78,6 +78,11 @@ module Bundler
 
           update(local_path, remote_path, :retrying)
         end
+      rescue Errno::EACCES
+        raise Bundler::PermissionError,
+          "Bundler does not have write access to create a temp directory " \
+          "within #{Dir.tmpdir}. Bundler must have write access to your " \
+          "systems temp directory to function properly. "
       end
 
       def etag_for(path)
diff --git a/spec/bundler/compact_index_client/updater_spec.rb b/spec/bundler/compact_index_client/updater_spec.rb
index 3c4f212b60..af24e58d5f 100644
--- a/spec/bundler/compact_index_client/updater_spec.rb
+++ b/spec/bundler/compact_index_client/updater_spec.rb
@@ -27,4 +27,18 @@ RSpec.describe Bundler::CompactIndexClient::Updater do
       end.to raise_error(Bundler::CompactIndexClient::Updater::MisMatchedChecksumError)
     end
   end
+
+  context "when bundler doesn't have permissions on Dir.tmpdir" do
+    let(:response) { double(:response, :body => "") }
+    let(:local_path) { Pathname("/tmp/localpath") }
+    let(:remote_path) { double(:remote_path) }
+
+    it "Errno::EACCES is raised" do
+      allow(Dir).to receive(:mktmpdir) { raise Errno::EACCES }
+
+      expect do
+        updater.update(local_path, remote_path)
+      end.to raise_error(Bundler::PermissionError)
+    end
+  end
 end