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Commit43e4377

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Handle empty-string edge cases correctly in strpos().
Commit9556aa0 rearranged the innards of text_position() in a waythat would make it not work for empty search strings. Which is fine,because all callers of that code special-case an empty pattern insome way. However, the primary use-case (text_position itself) gotspecial-cased incorrectly: historically it's returned 1 not 0 foran empty search string. Restore the historical behavior.Per complaint from Austin Drenski (via Shay Rojansky).Back-patch to v12 where it got broken.Discussion:https://postgr.es/m/CADT4RqAz7oN4vkPir86Kg1_mQBmBxCp-L_=9vRpgSNPJf0KRkw@mail.gmail.com
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3 files changed

+33
-1
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3 files changed

+33
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‎src/backend/utils/adt/varlena.c

Lines changed: 9 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1118,7 +1118,12 @@ text_position(text *t1, text *t2, Oid collid)
11181118
TextPositionStatestate;
11191119
intresult;
11201120

1121-
if (VARSIZE_ANY_EXHDR(t1)<1||VARSIZE_ANY_EXHDR(t2)<1)
1121+
/* Empty needle always matches at position 1 */
1122+
if (VARSIZE_ANY_EXHDR(t2)<1)
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return1;
1124+
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/* Otherwise, can't match if haystack is shorter than needle */
1126+
if (VARSIZE_ANY_EXHDR(t1)<VARSIZE_ANY_EXHDR(t2))
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return0;
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11241129
text_position_setup(t1,t2,collid,&state);
@@ -1272,6 +1277,9 @@ text_position_setup(text *t1, text *t2, Oid collid, TextPositionState *state)
12721277
* Advance to the next match, starting from the end of the previous match
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* (or the beginning of the string, on first call). Returns true if a match
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* is found.
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*
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* Note that this refuses to match an empty-string needle. Most callers
1282+
* will have handled that case specially and we'll never see it here.
12751283
*/
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staticbool
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text_position_next(TextPositionState*state)

‎src/test/regress/expected/strings.out

Lines changed: 18 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1371,6 +1371,24 @@ SELECT strpos('abcdef', 'xy') AS "pos_0";
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0
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(1 row)
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1374+
SELECT strpos('abcdef', '') AS "pos_1";
1375+
pos_1
1376+
-------
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1
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(1 row)
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SELECT strpos('', 'xy') AS "pos_0";
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pos_0
1382+
-------
1383+
0
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(1 row)
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SELECT strpos('', '') AS "pos_1";
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pos_1
1388+
-------
1389+
1
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(1 row)
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13741392
--
13751393
-- test replace
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--

‎src/test/regress/sql/strings.sql

Lines changed: 6 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -479,6 +479,12 @@ SELECT strpos('abcdef', 'cd') AS "pos_3";
479479

480480
SELECT strpos('abcdef','xy')AS"pos_0";
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482+
SELECT strpos('abcdef','')AS"pos_1";
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SELECT strpos('','xy')AS"pos_0";
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SELECT strpos('','')AS"pos_1";
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482488
--
483489
-- test replace
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--

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