SERVER-40343 Better handling of errors from PCRE in $regex expressions

2 files changed, 11 insertions, 9 deletions

diff --git a/jstests/aggregation/expressions/regex.js b/jstests/aggregation/expressions/regex.js
index fed44601ae7..618528ffa38 100644
--- a/jstests/aggregation/expressions/regex.js
+++ b/jstests/aggregation/expressions/regex.js
@@ -254,7 +254,7 @@
         assert.commandWorked(coll.insert({_id: 3, text: "ab\ncd"}));
 
         // LIMIT_MATCH option to limit the number of comparisons PCRE does internally.
-        testRegexFindAggForKey(2, {input: "$text", regex: "(*LIMIT_MATCH=1)fé"}, []);
+        testRegexAggException({input: "$text", regex: "(*LIMIT_MATCH=1)fé"}, 51156);
         testRegexFindAggForKey(2,
                                {input: "$text", regex: "(*LIMIT_MATCH=3)(fé)"},
                                [{"match": "fé", "idx": 2, "captures": ["fé"]}]);
@@ -270,8 +270,8 @@
         testRegexFindAggForKey(2,
                                {input: "$text", regex: String.raw `(*LIMIT_MATCH=5)(*UCP)^(\w+)`},
                                [{"match": "cafétéria", "idx": 0, "captures": ["cafétéria"]}]);
-        testRegexFindAggForKey(
-            2, {input: "$text", regex: String.raw `(*LIMIT_MATCH=1)(*UCP)^(\w+)`}, []);
+        testRegexAggException({input: "$text", regex: String.raw `(*LIMIT_MATCH=1)(*UCP)^(\w+)`},
+                              51156);
     })();
 
     (function testWithUnicodeData() {
diff --git a/jstests/aggregation/expressions/regex_limits.js b/jstests/aggregation/expressions/regex_limits.js
index bcf3679b001..8ae924f65eb 100644
--- a/jstests/aggregation/expressions/regex_limits.js
+++ b/jstests/aggregation/expressions/regex_limits.js
@@ -89,12 +89,14 @@
                          "captures": expectedOutputCaptures
                      }]);
 
-        // Weird case, stops matching after certain limit but doesn't error.
-        const bufferNoMatch = 2553;
-        pattern = "(d)".repeat(bufferNoMatch) + pattern;
-        testRegexAgg({input: "$z", regex: pattern}, []);
-
-        // Add more data and verify that PCRE throws an error.
+        // In this case, during execution, PCRE will hit the PCRE_ERROR_RECURSIONLIMIT because of
+        // high number of captures and return an error.
+        const bufferExecutionFailure = 2553;
+        pattern = "(d)".repeat(bufferExecutionFailure) + pattern;
+        testRegexAggException({input: "$z", regex: pattern}, 51156);
+
+        // Add one more capture group to the pattern so that it tips over the maximum regex length
+        // limit, and verify that PCRE throws an error while attempting to compile.
         pattern = "(d)" + pattern;
         testRegexAggException({input: "$z", regex: pattern}, 51111);
     })();