Make construct_[md_]array return a valid empty array for zero-size input.

If construct_array() or construct_md_array() were given a dimension of
zero, they'd produce an array that contains no elements but has positive
dimension.  This violates a general expectation that empty arrays should
have ndims = 0; in particular, while arrays like this print as empty,
they don't compare equal to other empty arrays.

Up to now we've expected callers to avoid making such calls and instead
be careful to call construct_empty_array() if there would be no elements.
But this has always been an easily missed case, and we've repeatedly had to
fix callers to do it right.  In bug #14826, Erwin Brandstetter pointed out
yet another such oversight, in ts_lexize(); and a bit of examination of
other call sites found at least two more with similar issues.  So let's
fix the problem centrally and permanently by changing these two functions
to construct a proper zero-D empty array whenever the array would be empty.

This renders a few explicit calls of construct_empty_array() redundant,
but the only such place I found that really seemed worth changing was in
ExecEvalArrayExpr().

Although this fixes some very old bugs, no back-patch: the problem is
pretty minor and the risk of changing behavior seems to outweigh the
benefit in stable branches.

Discussion: https://postgr.es/m/20170923125723.1448.39412@wrigleys.postgresql.org
Discussion: https://postgr.es/m/20570.1506198383@sss.pgh.pa.us

diff --git a/src/backend/executor/execExprInterp.c b/src/backend/executor/execExprInterp.c
index bd8a15d6c3159e662fa43285e2b1f64d3f363097..09abd46dda87f5cc4ba44ccf686e5840900c82c5 100644 (file)
--- a/src/backend/executor/execExprInterp.c
+++ b/src/backend/executor/execExprInterp.c
@@ -2131,14 +2131,6 @@ ExecEvalArrayExpr(ExprState *state, ExprEvalStep *op)
                Datum      *dvalues = op->d.arrayexpr.elemvalues;
                bool       *dnulls = op->d.arrayexpr.elemnulls;
 
-               /* Shouldn't happen here, but if length is 0, return empty array */
-               if (nelems == 0)
-               {
-                       *op->resvalue =
-                               PointerGetDatum(construct_empty_array(element_type));
-                       return;
-               }
-
                /* setup for 1-D array of the given length */
                ndims = 1;
                dims[0] = nelems;

diff --git a/src/backend/utils/adt/arrayfuncs.c b/src/backend/utils/adt/arrayfuncs.c
index e4101c9af0c7d471ed240346f4d8425514b9ebcd..d1f2fe7d95854429df2f7eb09a4558559f8b23af 100644 (file)
--- a/src/backend/utils/adt/arrayfuncs.c
+++ b/src/backend/utils/adt/arrayfuncs.c
@@ -3297,6 +3297,7 @@ array_map(FunctionCallInfo fcinfo, Oid retType, ArrayMapState *amstate)
  *
  * A palloc'd 1-D array object is constructed and returned.  Note that
  * elem values will be copied into the object even if pass-by-ref type.
+ * Also note the result will be 0-D not 1-D if nelems = 0.
  *
  * NOTE: it would be cleaner to look up the elmlen/elmbval/elmalign info
  * from the system catalogs, given the elmtype.  However, the caller is
@@ -3331,6 +3332,7 @@ construct_array(Datum *elems, int nelems,
  *
  * A palloc'd ndims-D array object is constructed and returned.  Note that
  * elem values will be copied into the object even if pass-by-ref type.
+ * Also note the result will be 0-D not ndims-D if any dims[i] = 0.
  *
  * NOTE: it would be cleaner to look up the elmlen/elmbval/elmalign info
  * from the system catalogs, given the elmtype.  However, the caller is
@@ -3362,12 +3364,12 @@ construct_md_array(Datum *elems,
                                 errmsg("number of array dimensions (%d) exceeds the maximum allowed (%d)",
                                                ndims, MAXDIM)));
 
-       /* fast track for empty array */
-       if (ndims == 0)
-               return construct_empty_array(elmtype);
-
        nelems = ArrayGetNItems(ndims, dims);
 
+       /* if ndims <= 0 or any dims[i] == 0, return empty array */
+       if (nelems <= 0)
+               return construct_empty_array(elmtype);
+
        /* compute required space */
        nbytes = 0;
        hasnulls = false;

diff --git a/src/test/regress/expected/tsearch.out b/src/test/regress/expected/tsearch.out
index b2fc9e207edb756a02b756e1fb9621ea3504d4ee..d63fb12f1de2a71eeff09f1a012a71ee072bd52a 100644 (file)
--- a/src/test/regress/expected/tsearch.out
+++ b/src/test/regress/expected/tsearch.out
@@ -618,6 +618,17 @@ SELECT * from ts_debug('english', '5aew.werc.ewr:8100/?xx');
  url_path | URL path    | /?xx                   | {simple}     | simple     | {/?xx}
 (3 rows)
 
+SELECT token, alias,
+  dictionaries, dictionaries is null as dnull, array_dims(dictionaries) as ddims,
+  lexemes, lexemes is null as lnull, array_dims(lexemes) as ldims
+from ts_debug('english', 'a title');
+ token |   alias   |  dictionaries  | dnull | ddims | lexemes | lnull | ldims 
+-------+-----------+----------------+-------+-------+---------+-------+-------
+ a     | asciiword | {english_stem} | f     | [1:1] | {}      | f     | 
+       | blank     | {}             | f     |       |         | t     | 
+ title | asciiword | {english_stem} | f     | [1:1] | {titl}  | f     | [1:1]
+(3 rows)
+
 -- to_tsquery
 SELECT to_tsquery('english', 'qwe & sKies ');
   to_tsquery   

diff --git a/src/test/regress/sql/tsearch.sql b/src/test/regress/sql/tsearch.sql
index e4b21f8f184ac0833ba8153a786faad587a79bf0..1c8520b3e917a9f7c562528325e2db828855a3c7 100644 (file)
--- a/src/test/regress/sql/tsearch.sql
+++ b/src/test/regress/sql/tsearch.sql
@@ -145,6 +145,10 @@ SELECT * from ts_debug('english', 'http://www.harewoodsolutions.co.uk/press.aspx
 SELECT * from ts_debug('english', 'http://aew.wer0c.ewr/id?ad=qwe&dw<span>');
 SELECT * from ts_debug('english', 'http://5aew.werc.ewr:8100/?');
 SELECT * from ts_debug('english', '5aew.werc.ewr:8100/?xx');
+SELECT token, alias,
+  dictionaries, dictionaries is null as dnull, array_dims(dictionaries) as ddims,
+  lexemes, lexemes is null as lnull, array_dims(lexemes) as ldims
+from ts_debug('english', 'a title');
 
 -- to_tsquery