Add coverage measurement mode by using gcov

This experimental feature is only for Ruby-core team, not for casual users.

Usage: `./configure --enable-gcov && make && make exam && make gcov`

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58817 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

tool/run-gcov.rb

@@ -0,0 +1,52 @@
+#!ruby
+require "pathname"
+require "open3"
+
+Pathname.glob("**/*.gcda").sort.each do |gcda|
+  if gcda.fnmatch("ext/*")
+    cwd, gcda = gcda.split.map {|s| s.to_s }
+    objdir = "."
+  else
+    cwd, objdir, gcda = ".", gcda.dirname.to_s, gcda.to_s
+  end
+  puts "$ gcov -lpbc -o #{ objdir } #{ gcda }"
+  out, err, _status = Open3.capture3("gcov", "-lpbc", "-o", objdir, gcda, chdir: cwd)
+  puts out
+  puts err
+
+  # a black list of source files that contains wrong #line directives
+  if err !~ %r(
+    \A(
+      Cannot\ open\ source\ file\ (
+         defs/keywords
+        |zonetab\.list
+        |enc/jis/props\.kwd
+        |parser\.c
+        |parser\.rl
+      )\n
+    )*\z
+  )x
+    raise "Unexpected gcov output"
+  end
+
+  if out !~ %r(
+    \A(
+      File\ .*\nLines\ executed:.*\n
+      (
+        Branches\ executed:.*\n
+        Taken\ at\ least\ once:.*\n
+      |
+        No\ branches\n
+      )?
+      (
+        Calls\ executed:.*\n
+      |
+        No\ calls\n
+      )?
+      Creating\ .*\n
+      \n
+    )+\z
+  )x
+    raise "Unexpected gcov output"
+  end
+end