Use the proper python interpretor for yum-dump.py on Fedora 21+

Fedora 21+ use dnf as the primary package manager.  Lamont added code in
12.5 to allow for a yum compat mode. This doesn't entirely work though
as we need yum-dump.py to correctly run.  We were parsing the shabang in
the yum binary to find the path to python.  On a dnf system the yum
binary is a bash script though so we were trying to run yum-dump.py
using bash which obviously fails.  I added a fallback method to use
python if the shebang parsing returns bash. With this in place AND the
yum package installed you can use the package resource on Fedora.

2 files changed, 18 insertions, 2 deletions

diff --git a/lib/chef/provider/package/yum.rb b/lib/chef/provider/package/yum.rb
index aff8dc9326..6258472a65 100644
--- a/lib/chef/provider/package/yum.rb
+++ b/lib/chef/provider/package/yum.rb
@@ -785,7 +785,7 @@ class Chef
           def python_bin
             yum_executable = which(yum_binary)
             if yum_executable && shabang?(yum_executable)
-              extract_interpreter(yum_executable)
+              shabang_or_fallback(extract_interpreter(yum_executable))
             else
               Chef::Log.warn("Yum executable not found or doesn't start with #!. Using default python.")
               "/usr/bin/python"
@@ -797,7 +797,17 @@ class Chef
           end
 
           def extract_interpreter(file)
-            ::File.open(file, 'r', &:readline)[2..-1].chomp
+            ::File.open(file, 'r', &:readline)[2..-1].strip
+          end
+
+          # dnf based systems have a yum shim that has /bin/bash as the interpreter. Don't use this.
+          def shabang_or_fallback(interpreter)
+            if interpreter == '/bin/bash'
+              Chef::Log.warn("Yum executable interpreter is /bin/bash. Falling back to default python.")
+              "/usr/bin/python"
+            else
+              interpreter
+            end
           end
 
           def shabang?(file)
diff --git a/spec/unit/provider/package/yum_spec.rb b/spec/unit/provider/package/yum_spec.rb
index 3fc0b807c9..b37a675bf2 100644
--- a/spec/unit/provider/package/yum_spec.rb
+++ b/spec/unit/provider/package/yum_spec.rb
@@ -1844,6 +1844,12 @@ EOF
       expect(@yc.python_bin).to eq("/usr/bin/python")
     end
 
+    it "should return /usr/bin/python if the interpreter is /bin/bash" do
+      other = StringIO.new("#!/bin/bash\n# The yum executable redirecting to dnf from dnf-yum compatible package.")
+      allow(::File).to receive(:open).with("/usr/bin/yum", "r") { |&b| r = b.call(other); other.rewind; r}
+      expect(@yc.python_bin).to eq("/usr/bin/python")
+    end
+
     it "should return the interpreter for yum" do
       other = StringIO.new("#!/usr/bin/super_python\n\nlasjdfdsaljf\nlasdjfs")
       allow(::File).to receive(:open).with("/usr/bin/yum", "r") { |&b| r = b.call(other); other.rewind; r}