Lint for distinct aggregate with more than one arg

sqlparser/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.21.1-dev
+
+- Lint for `DISTINCT` misuse in aggregate function calls.
+
 ## 0.21.0
 
 - Analysis support for new features in sqlite version 3.38.

sqlparser/lib/src/analysis/error.dart

@@ -80,6 +80,7 @@ enum AnalysisErrorType {
   missingPrimaryKey,
   noTypeNameInStrictTable,
   invalidTypeNameInStrictTable,
+  distinctAggregateWithWrongParameterCount,
   other,
   hint,
 }

sqlparser/lib/src/analysis/steps/linting_visitor.dart

@@ -204,6 +204,19 @@ class LintingVisitor extends RecursiveVisitor<void, void> {
     visitChildren(e, arg);
   }
 
+  @override
+  void visitExpressionFunctionParameters(ExprFunctionParameters e, void arg) {
+    if (e.distinct && e.parameters.length != 1) {
+      context.reportError(AnalysisError(
+        type: AnalysisErrorType.distinctAggregateWithWrongParameterCount,
+        message: 'A `DISTINCT` aggregate must have exactly one argument',
+        relevantNode: e.distinctKeyword ?? e,
+      ));
+    }
+
+    visitChildren(e, arg);
+  }
+
   @override
   void visitInvocation(SqlInvocation e, void arg) {
     final lowercaseCall = e.name.toLowerCase();

sqlparser/lib/src/ast/expressions/function.dart

@@ -66,6 +66,7 @@ class StarFunctionParameter extends FunctionParameters {
 
 class ExprFunctionParameters extends FunctionParameters {
   final bool distinct;
+  Token? distinctKeyword;
   List<Expression> parameters;
 
   ExprFunctionParameters({this.parameters = const [], this.distinct = false});

sqlparser/lib/src/reader/parser.dart

@@ -89,6 +89,13 @@ class Parser {
     return false;
   }
 
+  Token? _matchOneAndGet(TokenType type) {
+    if (_matchOne(type)) {
+      return _previous;
+    }
+    return null;
+  }
+
   /// Returns true if the next token is [type] or if the next two tokens are
   /// "NOT" followed by [type]. Does not consume any tokens.
   bool _checkWithNot(TokenType type) {
@@ -901,7 +908,7 @@ class Parser {
       return ExprFunctionParameters(parameters: const [])..synthetic = true;
     }
 
-    final distinct = _matchOne(TokenType.distinct);
+    final distinct = _matchOneAndGet(TokenType.distinct);
     final parameters = <Expression>[];
     final first = _peek;
 
@@ -909,7 +916,9 @@ class Parser {
       parameters.add(expression());
     } while (_matchOne(TokenType.comma));
 
-    return ExprFunctionParameters(distinct: distinct, parameters: parameters)
+    return ExprFunctionParameters(
+        distinct: distinct != null, parameters: parameters)
+      ..distinctKeyword = distinct
       ..setSpan(first, _previous);
   }
 

sqlparser/test/analysis/errors/misc_test.dart

@@ -0,0 +1,16 @@
+import 'package:sqlparser/sqlparser.dart';
+import 'package:test/test.dart';
+
+import '../data.dart';
+import 'utils.dart';
+
+void main() {
+  final engine = SqlEngine()..registerTable(demoTable);
+
+  test('warns about multiple parameters with DISTINCT', () {
+    engine
+        .analyze("SELECT group_concat(DISTINCT content, '-') FROM demo")
+        .expectError('DISTINCT',
+            type: AnalysisErrorType.distinctAggregateWithWrongParameterCount);
+  });
+}