fix failing unit test

parse/analyze.go

@@ -567,6 +567,12 @@ func (s *sqlAnalyzer) VisitExpressionFunctionCall(p0 *ExpressionFunctionCall) an
 		}
 	}
 
+	// callers of this visitor know that a nil return means a function does not
+	// return anything. We explicitly return nil instead of a nil *types.DataType
+	if returnType == nil {
+		return nil
+	}
+
 	return cast(p0, returnType)
 }
 
@@ -2252,6 +2258,14 @@ func (p *procedureAnalyzer) VisitProcedureStmtCall(p0 *ProcedureStmtCall) any {
 		p.errs.AddErr(p0, ErrViewMutatesState, `view procedure calls non-view procedure "%s"`, p0.Call.FunctionName())
 	}
 
+	// users can discard returns by simply not having receivers.
+	// if there are no receivers, we can return early.
+	if len(p0.Receivers) == 0 {
+		return &procedureStmtResult{
+			willReturn: exits,
+		}
+	}
+
 	// we do not have to capture all return values, but we need to ensure
 	// we do not have more receivers than return values.
 	if len(p0.Receivers) != len(callReturns) {

parse/functions.go

@@ -42,7 +42,7 @@ var (
 					return nil, wrapErrArgumentType(types.TextType, args[0])
 				}
 
-				return types.NullType, nil
+				return nil, nil
 			},
 			PGFormat: func(inputs []string, distinct bool, star bool) (string, error) {
 				if star {

parse/parse_test.go

@@ -1544,6 +1544,28 @@ func Test_Procedure(t *testing.T) {
 				},
 			},
 		},
+		{
+			name: "assigning a variable with error is invalid",
+			proc: `$a := error('error message');`,
+			err:  parse.ErrResultShape,
+		},
+		{
+			// this is a regression test for a previous bug
+			name: "discarding return values of a function is ok",
+			proc: `abs(-1);`,
+			want: &parse.ProcedureParseResult{
+				AST: []parse.ProcedureStmt{
+					&parse.ProcedureStmtCall{
+						Call: &parse.ExpressionFunctionCall{
+							Name: "abs",
+							Args: []parse.Expression{
+								exprLit(-1),
+							},
+						},
+					},
+				},
+			},
+		},
 	}
 
 	for _, tt := range tests {