Print exception's cause like Java

Print `cause` of the exception if the exception is not caught and printed
its backtraces and error message [Feature #8257]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@65393 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

NEWS

@@ -36,6 +36,12 @@ sufficient information, see the ChangeLog file or Redmine
 
     user = users.find {|user| cond(user) }
 
+* Print exception backtrace and error message in reverse order when the
+  exception is not caught and STDOUT is unchanged and a tty. [Feature #8661]
+
+* Print `cause` of the exception if the exception is not caught and printed
+  its backtraces and error message [Feature #8257]
+
 === Core classes updates (outstanding ones only)
 
 [Array]

eval_error.c

@@ -220,6 +220,29 @@ print_backtrace(const VALUE eclass, const VALUE errat, const VALUE str, int reve
     }
 }
 
+VALUE rb_get_message(VALUE exc);
+
+static void
+show_cause(VALUE errinfo, VALUE str, VALUE highlight, VALUE reverse)
+{
+    VALUE cause = rb_attr_get(errinfo, id_cause);
+    if (!NIL_P(cause)) {
+        volatile VALUE eclass = CLASS_OF(cause);
+        VALUE errat = rb_get_backtrace(cause);
+        VALUE emesg = rb_get_message(cause);
+        if (reverse) {
+            show_cause(cause, str, highlight, reverse);
+            print_errinfo(eclass, errat, emesg, str, highlight!=0);
+            print_backtrace(eclass, errat, str, FALSE);
+        }
+        else {
+            print_backtrace(eclass, errat, str, TRUE);
+            print_errinfo(eclass, errat, emesg, str, highlight!=0);
+            show_cause(cause, str, highlight, reverse);
+        }
+    }
+}
+
 void
 rb_error_write(VALUE errinfo, VALUE emesg, VALUE errat, VALUE str, VALUE highlight, VALUE reverse)
 {
@@ -254,17 +277,17 @@ rb_error_write(VALUE errinfo, VALUE emesg, VALUE errat, VALUE str, VALUE highlig
 	    len = p - (msg = buff);
 	}
 	write_warn2(str, msg, len);
+        show_cause(errinfo, str, highlight, reverse);
 	print_backtrace(eclass, errat, str, TRUE);
 	print_errinfo(eclass, errat, emesg, str, highlight!=0);
     }
     else {
 	print_errinfo(eclass, errat, emesg, str, highlight!=0);
 	print_backtrace(eclass, errat, str, FALSE);
+        show_cause(errinfo, str, highlight, reverse);
     }
 }
 
-VALUE rb_get_message(VALUE exc);
-
 void
 rb_ec_error_print(rb_execution_context_t * volatile ec, volatile VALUE errinfo)
 {

test/ruby/test_backtrace.rb

@@ -297,4 +297,36 @@ class TestBacktrace < Test::Unit::TestCase
     end
     assert_not_match(/\Acore#/, e.backtrace_locations[0].base_label)
   end
+
+  def test_notty_backtrace
+    err = ["-:1:in `<main>': unhandled exception"]
+    assert_in_out_err([], "raise", [], err)
+
+    err = ["-:2:in `foo': foo! (RuntimeError)",
+           "\tfrom -:4:in `<main>'"]
+    assert_in_out_err([], <<-"end;", [], err)
+    def foo
+      raise "foo!"
+    end
+    foo
+    end;
+
+    err = ["-:7:in `rescue in bar': bar! (RuntimeError)",
+           "\tfrom -:4:in `bar'",
+           "\tfrom -:9:in `<main>'",
+           "\t2: from -:9:in `<main>'",
+           "\t1: from -:5:in `bar'",
+           "-:2:in `foo': foo! (RuntimeError)"]
+    assert_in_out_err([], <<-"end;", [], err)
+    def foo
+      raise "foo!"
+    end
+    def bar
+      foo
+    rescue
+      raise "bar!"
+    end
+    bar
+    end;
+  end
 end