Quote all string values in EXPLAIN (FORMAT YAML) output.

While my previous attempt seems to always produce valid YAML, it
doesn't always produce YAML that means what it appears to mean,
because of tokens like "0xa" and "true", which without quotes will
be interpreted as integer or Boolean literals.  So, instead, just
quote everything that's not known to be a number, as we do for
JSON.

Dean Rasheed, with some changes to the comments by me.

src/backend/commands/explain.c

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1994-5, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/explain.c,v 1.205 2010/06/09 02:39:34 rhaas Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/explain.c,v 1.206 2010/06/10 01:26:30 rhaas Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1698,8 +1698,7 @@ ExplainPropertyList(const char *qlabel, List *data, ExplainState *es)
 
 		case EXPLAIN_FORMAT_YAML:
 			ExplainYAMLLineStarting(es);
-			escape_yaml(es->str, qlabel);
-			appendStringInfoChar(es->str, ':');
+			appendStringInfo(es->str, "%s: ", qlabel);
 			foreach(lc, data)
 			{
 				appendStringInfoChar(es->str, '\n');
@@ -1759,6 +1758,9 @@ ExplainProperty(const char *qlabel, const char *value, bool numeric,
 		case EXPLAIN_FORMAT_YAML:
 			ExplainYAMLLineStarting(es);
 			appendStringInfo(es->str, "%s: ", qlabel);
+			if (numeric)
+				appendStringInfoString(es->str, value);
+			else
 				escape_yaml(es->str, value);
 			break;
 	}
@@ -1857,8 +1859,7 @@ ExplainOpenGroup(const char *objtype, const char *labelname,
 			ExplainYAMLLineStarting(es);
 			if (labelname)
 			{
-				escape_yaml(es->str, labelname);
-				appendStringInfoChar(es->str, ':');
+				appendStringInfo(es->str, "%s: ", labelname);
 				es->grouping_stack = lcons_int(1, es->grouping_stack);
 			}
 			else
@@ -2152,48 +2153,17 @@ escape_json(StringInfo buf, const char *str)
 }
 
 /*
- * YAML is a superset of JSON, so we can use JSON escaping when escaping is
- * needed.  However, some things that need to be quoted in JSON don't require
- * quoting in YAML, and we prefer not to quote unnecessarily, to improve
- * readability.
- *
- * Unfortunately, the YAML quoting rules are ridiculously complicated -- as
- * documented in sections 5.3 and 7.3.3 of http://yaml.org/spec/1.2/spec.html
- * -- and it doesn't seem worth expending a large amount of energy to avoid
- * all unnecessary quoting, so we just do something (sort of) simple: we quote
- * any string which is empty; any string which contains characters other than
- * alphanumerics, period, underscore, or space; or begins or ends with a
- * space.  The exception for period is mostly so that floating-point numbers
- * (e.g., cost values) won't be quoted.
+ * YAML is a superset of JSON; unfortuantely, the YAML quoting rules are
+ * ridiculously complicated -- as documented in sections 5.3 and 7.3.3 of
+ * http://yaml.org/spec/1.2/spec.html -- so we chose to just quote everything.
+ * Empty strings, strings with leading or trailing whitespace, and strings
+ * containing a variety of special characters must certainly be quoted or the
+ * output is invalid; and other seemingly harmless strings like "0xa" or
+ * "true" must be quoted, lest they be interpreted as a hexadecimal or Boolean
+ * constant rather than a string.
  */
 static void
 escape_yaml(StringInfo buf, const char *str)
 {
-	bool		needs_quoting = false;
-
-#define is_safe_yaml(x) \
-	(isalnum(((unsigned char) x)) || (x) == '.' || (x) == '_')
-
-	if (!is_safe_yaml(str[0]))
-		needs_quoting = true;
-	else
-	{
-		const char *p;
-
-		for (p = str; *p; p++)
-		{
-			if (*p != ' ' && !is_safe_yaml(*p))
-			{
-				needs_quoting = true;
-				break;
-			}
-		}
-		if (!*p && p[-1] == ' ')
-			needs_quoting = true;
-	}
-
-	if (needs_quoting)
 	escape_json(buf, str);
-	else
-		appendStringInfoString(buf, str);
 }