Auto merge of #6343 - nesaulov:fix-nil-backtrace, r=colby-swandale

Fix failure when exception backtrace is nil

Resolves #6342
### What was the end-user problem that led to this PR?

Instead of throwing a readable error, Bundler failed and generated an issue report template (see details in #6342).

### What was your diagnosis of the problem?

My diagnosis was that nil safety is hard in Ruby.

### What is your fix for the problem, implemented in this PR?

To check whether backtrace is nil before sending it a `take_while` method.

### Why did you choose this fix out of the possible options?

I chose this fix because I see no other solutions.

(cherry picked from commit 7f4c1a81b7b92e234fce0e3592d27c396d2451ac)

2 files changed, 31 insertions, 1 deletions

diff --git a/lib/bundler/cli/exec.rb b/lib/bundler/cli/exec.rb
index d6ac453676..386565c575 100644
--- a/lib/bundler/cli/exec.rb
+++ b/lib/bundler/cli/exec.rb
@@ -77,7 +77,7 @@ module Bundler
     rescue Exception => e # rubocop:disable Lint/RescueException
       Bundler.ui = ui
       Bundler.ui.error "bundler: failed to load command: #{cmd} (#{file})"
-      backtrace = e.backtrace.take_while {|bt| !bt.start_with?(__FILE__) }
+      backtrace = e.backtrace ? e.backtrace.take_while {|bt| !bt.start_with?(__FILE__) } : []
       abort "#{e.class}: #{e.message}\n  #{backtrace.join("\n  ")}"
     end
 
diff --git a/spec/commands/exec_spec.rb b/spec/commands/exec_spec.rb
index d094c1d578..4a2702fe83 100644
--- a/spec/commands/exec_spec.rb
+++ b/spec/commands/exec_spec.rb
@@ -606,6 +606,36 @@ RSpec.describe "bundle exec" do
       it_behaves_like "it runs"
     end
 
+    context "the executable raises an error without a backtrace", :bundler => "< 2" do
+      let(:executable) { super() << "\nclass Err < Exception\ndef backtrace; end;\nend\nraise Err" }
+      let(:exit_code) { 1 }
+      let(:expected) { super() << "\nbundler: failed to load command: #{path} (#{path})" }
+      let(:expected_err) do
+        if ENV["BUNDLER_SPEC_SUB_VERSION"] == "1.98"
+          "Err: Err"
+        else
+          "bundler: failed to load command: #{path} (#{path})\nErr: Err"
+        end
+      end
+
+      it_behaves_like "it runs"
+    end
+
+    context "the executable raises an error without a backtrace", :bundler => "2" do
+      let(:executable) { super() << "\nclass Err < Exception\ndef backtrace; end;\nend\nraise Err" }
+      let(:exit_code) { 1 }
+      let(:expected_err) { "bundler: failed to load command: #{path} (#{path})\nErr: Err" }
+      let(:expected) do
+        if ENV["BUNDLER_SPEC_SUB_VERSION"] == "1.98"
+          super() << "\nbundler: failed to load command: #{path} (#{path})"
+        else
+          super()
+        end
+      end
+
+      it_behaves_like "it runs"
+    end
+
     context "when the file uses the current ruby shebang" do
       let(:shebang) { "#!#{Gem.ruby}" }
       it_behaves_like "it runs"