CBL-6371: Unnest Query run after delete index produces obtuse error m…

…essage (#2178)

We enhanced the error by adding to the original message, "This table is referenced by an array index, which may have been deleted."

* We also enhanced the error message of FTS index in the similar situation.

C/tests/c4ArrayIndexTest.cc

@@ -358,26 +358,30 @@ TEST_CASE_METHOD(ArrayIndexTest, "CRUD Array Index Shared Path", "[C][ArrayIndex
     bool deleted = c4coll_deleteIndex(coll, "phones"_sl, ERROR_INFO());
     REQUIRE(deleted);
 
-    // We must re-create the Query objects because we deleted the index - which means the unnest tables may be missing.
-    cityQuery = c4query_new2(
-            db, kC4N1QLQuery,
-            R"(SELECT p.pid, c.address.city, c.address.state FROM profiles AS p UNNEST p.contacts AS c WHERE c.address.state = "CA")"_sl,
-            nullptr, ERROR_INFO());
-    REQUIRE(cityQuery);
+    // cityQuery is not affected by the deletion of index "phones"
+    queryenum = REQUIRED(c4query_run(cityQuery, nullslice, nullptr));
+    validateQuery(queryenum, {
+                                     R"(["p-0001", "San Pedro", "CA"])",
+                                     R"(["p-0001", "San Pedro", "CA"])",
+                             });
+
+    // phoneQuery is affected by the deletion of index "phones"
+    // Following error will be logged,
+    // 2024-10-29T21:14:28.226339 DB ERROR SQLite error (code 1): no such table: 152b9815998e188eb99eb1612aafbb3ee6031535 in "SELECT fl_result(fl_value(prof.body, 'pid')), fl_result(fl_unnested_value(c.body, 'address.city')), fl_result(fl_unnested_value(c.body, 'address.state')), fl_result(fl_unnested_value(p.body, 'type')), fl_result(fl_unnested_value(p.body, 'numbers')) FROM "kv_.profiles" AS prof JOIN bc89db8a20fe759bf161b84adf2294d9bfe0c88d AS c ON c.docid=prof.rowid JOIN "152b9815998e188eb99eb1612aafbb3ee6031535" AS p ON p.docid=c.rowid WHERE fl_unnested_value(p.body, 'type') = 'mobile'". This table is referenced by an array index, which may have been deleted.
+    C4Error error;
+    queryenum = c4query_run(phoneQuery, nullslice, &error);
+    CHECK(!queryenum);  // This query relies on the index that has been deleted.
+    CHECK((error.domain == SQLiteDomain && error.code == 1));
 
+    // Recompile the query
     phoneQuery = c4query_new2(
             db, kC4N1QLQuery,
             R"(SELECT prof.pid, c.address.city, c.address.state, p.type, p.numbers FROM profiles AS prof UNNEST prof.contacts AS c UNNEST c.phones AS p WHERE p.type = "mobile")"_sl,
             nullptr, ERROR_INFO());
     REQUIRE(phoneQuery);
+    queryenum = c4query_run(phoneQuery, nullslice, &error);
+    CHECK(queryenum);
 
-
-    queryenum = REQUIRED(c4query_run(cityQuery, nullslice, nullptr));
-    validateQuery(queryenum, {
-                                     R"(["p-0001", "San Pedro", "CA"])",
-                                     R"(["p-0001", "San Pedro", "CA"])",
-                             });
-    queryenum = REQUIRED(c4query_run(phoneQuery, nullslice, nullptr));
     validateQuery(queryenum, {
                                      R"(["p-0001", "San Pedro", "CA", "mobile", ["310-9601308"]])",
                                      R"(["p-0001", "San Pedro", "CA", "mobile", ["310-4833623"]])",
@@ -654,6 +658,9 @@ TEST_CASE_METHOD(ArrayIndexTest, "Unnest Without Alias", "[C][Unnest]") {
 
 // 7. TestUnnestArrayLiteralNotSupport
 TEST_CASE_METHOD(ArrayIndexTest, "Unnest Array Literal Not Supported", "[C][Unnest]") {
+    C4Collection* coll = createCollection(db, {"profiles"_sl, "_default"_sl});
+    importTestData(coll);
+
     C4Error err{};
     c4::ref query = c4query_new2(
             db, kC4N1QLQuery,

C/tests/c4QueryTest.cc

@@ -1487,6 +1487,15 @@ TEST_CASE_METHOD(CollectionTest, "C4Query FTS Multiple collections", "[Query][C]
 
     CHECK(run().size() == 50);
     CHECK(runFTS().size() == 50);
+
+    auto deleted = c4coll_deleteIndex(names, C4STR("byStreet"), nullptr);
+    CHECK(deleted);
+    // The query won't run after the index is deleted. We should see following error in the log,
+    // 2024-10-29T20:57:00.896439 DB ERROR SQLite error (code 1): no such table: kv_.namedscope.names::by\Street in "SELECT "namedscope.names".rowid, offsets(fts1."kv_.namedscope.names::by\Street"), offsets(fts2."kv_.wiki::by\Text"), fl_result("namedscope.names".key), fl_result(wiki.key) FROM "kv_.namedscope.names" AS "namedscope.names" INNER JOIN "kv_.wiki" AS wiki ON (fl_value("namedscope.names".body, 'birthday') != fl_value(wiki.body, 'title')) JOIN "kv_.namedscope.names::by\Street" AS fts1 ON fts1.docid = "namedscope.names".rowid JOIN "kv_.wiki::by\Text" AS fts2 ON fts2.docid = wiki.rowid WHERE fts1."kv_.namedscope.names::by\Street" MATCH 'Hwy' AND fts2. This table is referenced by an FTS index, which may have been deleted.
+    C4Error error;
+    auto    qenum = c4query_run(query, c4str(nullptr), &error);
+    CHECK(!qenum);
+    CHECK((error.domain == SQLiteDomain && error.code == 1));
 }
 
 #pragma mark - OBSERVERS:

LiteCore/Storage/SQLiteDataFile.cc

@@ -36,6 +36,7 @@
 #include <sqlite3.h>
 #include <sstream>
 #include <mutex>
+#include <regex>
 #include <thread>
 #include <cinttypes>
 #ifdef _WIN32
@@ -114,6 +115,28 @@ namespace litecore {
 
     void LogStatement(const SQLite::Statement& st) { LogTo(SQL, "... %s", st.getQuery().c_str()); }
 
+    static std::pair<bool, std::string> enhanceSQLiteErrorLog(int errCode, const char* msg) {
+        std::regex  noTableRegx{"no such table: (\\S+) in "};
+        std::cmatch match;
+        const char* extra = nullptr;
+        if ( std::regex_search(msg, match, noTableRegx) ) {
+            if ( std::regex_search(match.suffix().str(), std::regex{"fl_unnested_value"})
+                 && std::regex_match(match[1].str(), std::regex{"[0-9a-z]{40}"}) ) {
+                extra = "This table is referenced by an array index, which may have been deleted.";
+            } else if ( std::regex_match(match[1].str(), std::regex{"kv_\\..+::.+"}) ) {
+                // example target: match[1].str() = "kv_.namedscope.names::by\\Street"
+                // where "::" = KeyStore::kIndexSeparator
+                extra = "This table is referenced by an FTS index, which may have been deleted.";
+            }
+        }
+        std::string enhanced;
+        if ( extra ) {
+            enhanced = msg;
+            enhanced += ". "s + extra;
+        }
+        return std::make_pair(extra, enhanced);
+    }
+
     static void sqlite3_log_callback(C4UNUSED void* pArg, int errCode, const char* msg) {
         switch ( errCode & 0xFF ) {
             case SQLITE_OK:
@@ -132,7 +155,11 @@ namespace litecore {
                 LogWarn(DBLog, "SQLite warning: %s", msg);
                 break;
             default:
-                LogError(DBLog, "SQLite error (code %d): %s", errCode, msg);
+                {
+                    auto [enhanced, enhancedMsg] = enhanceSQLiteErrorLog(errCode, msg);
+                    if ( enhanced ) msg = enhancedMsg.c_str();
+                    LogError(DBLog, "SQLite error (code %d): %s", errCode, msg);
+                }
                 break;
         }
     }