Add post-merge capability to pre-commit-hook.rb

This will make it possible to run a post-merge check when
pre-commit-hook.rb is referenced as a symlink from .git/hooks/post-merge

The kind of check you're going to do is entirely dependant on the
basename of the file, which is a little weird but convenient.

Verification is a little tricky on this. Coming soon.

tools/dev/pre-commit-hook.rb

@@ -18,12 +18,38 @@
 #
 # ln -sf <this file> <path to commit hook>
 
+def merge_error_message
+  msg = []
+  msg << "[*] This merge contains modules failing msftidy.rb"
+  msg << "[*] Please fix this if you intend to publish these"
+  msg << "[*] modules to a popular metasploit-framework repo"
+  puts "-" * 72
+  puts msg.join("\n")
+  puts "-" * 72
+end
+
 valid = true # Presume validity
 files_to_check = []
 
-results = %x[git diff --cached --name-only]
+# Who called us? If it's a post-merge check things operate a little
+# differently.
 
-results.each_line do |fname|
+case $0
+when /post-merge/
+  base_caller = :post_merge
+when /pre-commit/
+  base_caller = :post_commit
+else
+  base_caller = :msftidy
+end
+
+if base_caller == :post_merge
+  changed_files = %x[git diff --name-only HEAD^ HEAD]
+else
+  changed_files = %x[git diff --cached --name-only]
+end
+
+changed_files.each_line do |fname|
   fname.strip!
   next unless File.exist?(fname) and File.file?(fname)
   next unless fname =~ /modules.+\.rb/
@@ -31,9 +57,9 @@ results.each_line do |fname|
 end
 
 if files_to_check.empty?
-  puts "--- No Metasploit modules to check, committing. ---"
+  puts "--- No Metasploit modules to check ---"
 else
-  puts "--- Checking module syntax with tools/msftidy.rb ---"
+  puts "--- Checking new and changed module syntax with tools/msftidy.rb ---"
   files_to_check.each do |fname|
     cmd = "ruby ./tools/msftidy.rb  #{fname}"
     msftidy_output= %x[ #{cmd} ]
@@ -43,12 +69,18 @@ else
       puts line
     end
   end
-  puts "-" * 52
+  puts "-" * 72
 end
 
 unless valid
-  puts "msftidy.rb objected, aborting commit"
-  puts "To bypass this check use: git commit --no-verify"
-  puts "-" * 52
-  exit(1)
+  if base_caller == :post_merge
+    puts merge_error_message
+    exit(0x10)
+  else
+    puts "[!] msftidy.rb objected, aborting commit"
+    puts "[!] To bypass this check use: git commit --no-verify"
+    puts "-" * 72
+    exit(0x01)
+  end
+
 end