Several fixes for EXPLAIN (FORMAT YAML), plus one for EXPLAIN (FORMAT JSON).

ExplainSeparatePlans() was busted for both JSON and YAML output - the present
code is a holdover from the original version of my machine-readable explain
patch, which didn't have the grouping_stack machinery.  Also, fix an odd
distribution of labor between ExplainBeginGroup() and ExplainYAMLLineStarting()
when marking lists with "- ", with each providing one character.  This broke
the output format for multi-query statements.  Also, fix ExplainDummyGroup()
for the YAML output format.

Along the way, make the YAML format use escape_yaml() in situations where the
JSON format uses escape_json().  Right now, it doesn't matter because all the
values are known not to need escaping, but it seems safer this way.  Finally,
I added some comments to better explain what the YAML output format is doing.

Greg Sabino Mullane reported the issues with multi-query statements.
Analysis and remaining cleanups by me.

diff --git a/src/backend/commands/explain.c b/src/backend/commands/explain.c
index e63b857..f4a6aa4 100644 (file)
--- a/src/backend/commands/explain.c
+++ b/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 1.196 2009/12/15 04:57:47 rhaas Exp $
+ *       $PostgreSQL: pgsql/src/backend/commands/explain.c,v 1.197 2009/12/16 22:16:16 rhaas Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1694,10 +1694,7 @@ 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);
+                       escape_yaml(es->str, value);
                        break;
        }
 }
@@ -1785,15 +1782,23 @@ ExplainOpenGroup(const char *objtype, const char *labelname,
                        break;
 
                case EXPLAIN_FORMAT_YAML:
+
+                       /*
+                        * In YAML format, the grouping stack is an integer list.  0 means
+                        * we've emitted nothing at this grouping level AND this grouping
+                        * level is unlabelled and must be marked with "- ".  See
+                        * ExplainYAMLLineStarting().
+                        */
                        ExplainYAMLLineStarting(es);
                        if (labelname)
                        {
-                               appendStringInfo(es->str, "%s:", labelname);
+                               escape_yaml(es->str, labelname);
+                               appendStringInfoChar(es->str, ':');
                                es->grouping_stack = lcons_int(1, es->grouping_stack);
                        }
                        else
                        {
-                               appendStringInfoChar(es->str, '-');
+                               appendStringInfoString(es->str, "- ");
                                es->grouping_stack = lcons_int(0, es->grouping_stack);
                        }
                        es->indent++;
@@ -1868,8 +1873,15 @@ ExplainDummyGroup(const char *objtype, const char *labelname, ExplainState *es)
                case EXPLAIN_FORMAT_YAML:
                        ExplainYAMLLineStarting(es);
                        if (labelname)
-                               appendStringInfo(es->str, "%s:", labelname);
-                       appendStringInfoString(es->str, objtype);
+                       {
+                               escape_yaml(es->str, labelname);
+                               appendStringInfoString(es->str, ": ");
+                       }
+                       else
+                       {
+                               appendStringInfoString(es->str, "- ");
+                       }
+                       escape_yaml(es->str, objtype);
                        break;
        }
 }
@@ -1946,18 +1958,14 @@ ExplainSeparatePlans(ExplainState *es)
        switch (es->format)
        {
                case EXPLAIN_FORMAT_TEXT:
-               case EXPLAIN_FORMAT_YAML:
                        /* add a blank line */
                        appendStringInfoChar(es->str, '\n');
                        break;
 
                case EXPLAIN_FORMAT_XML:
-                       /* nothing to do */
-                       break;
-
                case EXPLAIN_FORMAT_JSON:
-                       /* must have a comma between array elements */
-                       appendStringInfoChar(es->str, ',');
+               case EXPLAIN_FORMAT_YAML:
+                       /* nothing to do */
                        break;
        }
 }
@@ -2011,6 +2019,12 @@ ExplainJSONLineEnding(ExplainState *es)
 
 /*
  * Indent a YAML line.
+ *
+ * YAML lines are ordinarily indented by two spaces per indentation level.
+ * The text emitted for each property begins just prior to the preceding
+ * line-break, except for the first property in an unlabelled group, for which
+ * it begins immediately after the "- " that introduces the group.  The first
+ * property of the group appears on the same line as the opening "- ".
  */
 static void
 ExplainYAMLLineStarting(ExplainState *es)
@@ -2018,7 +2032,6 @@ ExplainYAMLLineStarting(ExplainState *es)
        Assert(es->format == EXPLAIN_FORMAT_YAML);
        if (linitial_int(es->grouping_stack) == 0)
        {
-               appendStringInfoChar(es->str, ' ');
                linitial_int(es->grouping_stack) = 1;
        }
        else
@@ -2074,7 +2087,8 @@ escape_json(StringInfo buf, const char *str)
 }
 
 /*
- * YAML is a superset of JSON: if we find quotable characters, we call escape_json
+ * YAML is a superset of JSON: if we find quotable characters, we call
+ * escape_json.  If not, we emit the property unquoted for better readability.
  */
 static void
 escape_yaml(StringInfo buf, const char *str)