Polishing.

Revisit DISTINCT count queries when primary alias isn't set. HQL can handle such queries, JPQL and EQL transformers now fail properly.

See #3744

spring-data-jpa/src/main/java/org/springframework/data/jpa/repository/query/EqlCountQueryTransformer.java

@@ -99,6 +99,10 @@ private QueryRendererBuilder getDistinctCountSelection(QueryTokenStream selectio
 
 		if (countSelection.requiresPrimaryAlias()) {
 			// constructor
+			if (primaryFromAlias == null) {
+				throw new IllegalStateException(
+						"Primary alias must be set for DISTINCT count selection using constructor expressions");
+			}
 			nested.append(QueryTokens.token(primaryFromAlias));
 		} else {
 			// keep all the select items to distinct against

spring-data-jpa/src/main/java/org/springframework/data/jpa/repository/query/JpqlCountQueryTransformer.java

@@ -100,6 +100,10 @@ private QueryRendererBuilder getDistinctCountSelection(QueryTokenStream selectio
 
 		if (countSelection.requiresPrimaryAlias()) {
 			// constructor
+			if (primaryFromAlias == null) {
+				throw new IllegalStateException(
+						"Primary alias must be set for DISTINCT count selection using constructor expressions");
+			}
 			nested.append(QueryTokens.token(primaryFromAlias));
 		} else {
 			// keep all the select items to distinct against

spring-data-jpa/src/main/java/org/springframework/data/jpa/repository/query/QueryTransformers.java

@@ -71,6 +71,42 @@ static CountSelectionTokenStream create(QueryTokenStream selection) {
 			return new CountSelectionTokenStream(target, containsNew);
 		}
 
+		/**
+		 * Filter constructor expression and return the selection list of the constructor.
+		 *
+		 * @return the selection list of the constructor without {@code NEW}, class name, and the first level of
+		 *         parentheses.
+		 * @since 3.5.2
+		 */
+		public CountSelectionTokenStream withoutConstructorExpression() {
+
+			if (!requiresPrimaryAlias()) {
+				return this;
+			}
+
+			List<QueryToken> target = new ArrayList<>(size());
+			int nestingLevel = 0;
+
+			for (QueryToken token : this) {
+
+				if (token.equals(TOKEN_OPEN_PAREN)) {
+					nestingLevel++;
+					continue;
+				}
+
+				if (token.equals(TOKEN_CLOSE_PAREN)) {
+					nestingLevel--;
+					continue;
+				}
+
+				if (nestingLevel > 0) {
+					target.add(token);
+				}
+			}
+
+			return new CountSelectionTokenStream(target, requiresPrimaryAlias());
+		}
+
 		@Override
 		public Iterator<QueryToken> iterator() {
 			return tokens.iterator();

spring-data-jpa/src/test/java/org/springframework/data/jpa/repository/query/HqlQueryTransformerTests.java

@@ -41,6 +41,7 @@
  *
  * @author Greg Turnquist
  * @author Christoph Strobl
+ * @author Mark Paluch
  */
 class HqlQueryTransformerTests {
 
@@ -182,6 +183,12 @@ void multipleAliasesShouldBeGathered() {
 
 	@Test
 	void createsCountQueryCorrectly() {
+
+		assertCountQuery("SELECT id FROM Person", "SELECT count(id) FROM Person");
+		assertCountQuery("SELECT p.id FROM Person p", "SELECT count(p) FROM Person p");
+		assertCountQuery("SELECT id FROM Person p", "SELECT count(id) FROM Person p");
+		assertCountQuery("SELECT id, name FROM Person", "SELECT count(*) FROM Person");
+		assertCountQuery("SELECT id, name FROM Person p", "SELECT count(p) FROM Person p");
 		assertCountQuery(QUERY, COUNT_QUERY);
 	}
 
@@ -204,6 +211,9 @@ void createsCountQueryForConstructorQueries() {
 
 		assertCountQuery("select distinct new com.example.User(u.name) from User u where u.foo = ?1",
 				"select count(distinct u) from User u where u.foo = ?1");
+
+		assertCountQuery("select distinct new com.example.User(name, lastname) from User where foo = ?1",
+				"select count(distinct name, lastname) from User where foo = ?1");
 	}
 
 	@Test
@@ -913,7 +923,7 @@ void queryParserPicksCorrectAliasAmidstMultipleAlises() {
 	void countQueryShouldWorkEvenWithoutExplicitAlias() {
 
 		assertCountQuery("FROM BookError WHERE portal = :portal",
-				"select count(__) FROM BookError AS __ WHERE portal = :portal");
+				"select count(__) FROM BookError WHERE portal = :portal");
 
 		assertCountQuery("FROM BookError b WHERE portal = :portal",
 				"select count(b) FROM BookError b WHERE portal = :portal");
@@ -1107,15 +1117,15 @@ void aliasesShouldNotOverlapWithSortProperties() {
 	@Test // GH-3269, GH-3689
 	void createsCountQueryUsingAliasCorrectly() {
 
-		assertCountQuery("select distinct 1 as x from Employee", "select count(distinct 1) from Employee AS __");
-		assertCountQuery("SELECT DISTINCT abc AS x FROM T", "SELECT count(DISTINCT abc) FROM T AS __");
-		assertCountQuery("select distinct a as x, b as y from Employee", "select count(distinct a, b) from Employee AS __");
+		assertCountQuery("select distinct 1 as x from Employee", "select count(distinct 1) from Employee");
+		assertCountQuery("SELECT DISTINCT abc AS x FROM T", "SELECT count(DISTINCT abc) FROM T");
+		assertCountQuery("select distinct a as x, b as y from Employee", "select count(distinct a, b) from Employee");
 		assertCountQuery("select distinct sum(amount) as x from Employee GROUP BY n",
-				"select count(distinct sum(amount)) from Employee AS __ GROUP BY n");
+				"select count(distinct sum(amount)) from Employee GROUP BY n");
 		assertCountQuery("select distinct a, b, sum(amount) as c, d from Employee GROUP BY n",
-				"select count(distinct a, b, sum(amount), d) from Employee AS __ GROUP BY n");
+				"select count(distinct a, b, sum(amount), d) from Employee GROUP BY n");
 		assertCountQuery("select distinct a, count(b) as c from Employee GROUP BY n",
-				"select count(distinct a, count(b)) from Employee AS __ GROUP BY n");
+				"select count(distinct a, count(b)) from Employee GROUP BY n");
 		assertCountQuery("select distinct substring(e.firstname, 1, position('a' in e.lastname)) as x from from Employee",
 				"select count(distinct substring(e.firstname, 1, position('a' in e.lastname))) from from Employee");
 	}