Fix pipeline batch results not closing pipeline

when error occurs while reading directly from results instead of using
a callback.

https://github.com/jackc/pgx/issues/1578

batch.go

@@ -381,17 +381,13 @@ func (br *pipelineBatchResults) Close() error {
 		}
 	}()
 
-	if br.err != nil {
-		return br.err
-	}
-
-	if br.lastRows != nil && br.lastRows.err != nil {
+	if br.err == nil && br.lastRows != nil && br.lastRows.err != nil {
 		br.err = br.lastRows.err
 		return br.err
 	}
 
 	if br.closed {
-		return nil
+		return br.err
 	}
 
 	// Read and run fn for all remaining items

batch_test.go

@@ -720,6 +720,28 @@ func TestTxSendBatchRollback(t *testing.T) {
 	})
 }
 
+// https://github.com/jackc/pgx/issues/1578
+func TestSendBatchErrorWhileReadingResultsWithoutCallback(t *testing.T) {
+	t.Parallel()
+
+	pgxtest.RunWithQueryExecModes(context.Background(), t, defaultConnTestRunner, nil, func(ctx context.Context, t testing.TB, conn *pgx.Conn) {
+		batch := &pgx.Batch{}
+		batch.Queue("select 4 / $1::int", 0)
+
+		batchResult := conn.SendBatch(ctx, batch)
+
+		_, execErr := batchResult.Exec()
+		require.Error(t, execErr)
+
+		closeErr := batchResult.Close()
+		require.Equal(t, execErr, closeErr)
+
+		// Try to use the connection.
+		_, err := conn.Exec(ctx, "select 1")
+		require.NoError(t, err)
+	})
+}
+
 func TestConnBeginBatchDeferredError(t *testing.T) {
 	t.Parallel()
 

conn.go

@@ -975,7 +975,7 @@ func (c *Conn) sendBatchQueryExecModeExec(ctx context.Context, b *Batch) *batchR
 
 func (c *Conn) sendBatchQueryExecModeCacheStatement(ctx context.Context, b *Batch) (pbr *pipelineBatchResults) {
 	if c.statementCache == nil {
-		return &pipelineBatchResults{ctx: ctx, conn: c, err: errDisabledStatementCache}
+		return &pipelineBatchResults{ctx: ctx, conn: c, err: errDisabledStatementCache, closed: true}
 	}
 
 	distinctNewQueries := []*pgconn.StatementDescription{}
@@ -1007,7 +1007,7 @@ func (c *Conn) sendBatchQueryExecModeCacheStatement(ctx context.Context, b *Batc
 
 func (c *Conn) sendBatchQueryExecModeCacheDescribe(ctx context.Context, b *Batch) (pbr *pipelineBatchResults) {
 	if c.descriptionCache == nil {
-		return &pipelineBatchResults{ctx: ctx, conn: c, err: errDisabledDescriptionCache}
+		return &pipelineBatchResults{ctx: ctx, conn: c, err: errDisabledDescriptionCache, closed: true}
 	}
 
 	distinctNewQueries := []*pgconn.StatementDescription{}
@@ -1074,18 +1074,18 @@ func (c *Conn) sendBatchExtendedWithDescription(ctx context.Context, b *Batch, d
 
 		err := pipeline.Sync()
 		if err != nil {
-			return &pipelineBatchResults{ctx: ctx, conn: c, err: err}
+			return &pipelineBatchResults{ctx: ctx, conn: c, err: err, closed: true}
 		}
 
 		for _, sd := range distinctNewQueries {
 			results, err := pipeline.GetResults()
 			if err != nil {
-				return &pipelineBatchResults{ctx: ctx, conn: c, err: err}
+				return &pipelineBatchResults{ctx: ctx, conn: c, err: err, closed: true}
 			}
 
 			resultSD, ok := results.(*pgconn.StatementDescription)
 			if !ok {
-				return &pipelineBatchResults{ctx: ctx, conn: c, err: fmt.Errorf("expected statement description, got %T", results)}
+				return &pipelineBatchResults{ctx: ctx, conn: c, err: fmt.Errorf("expected statement description, got %T", results), closed: true}
 			}
 
 			// Fill in the previously empty / pending statement descriptions.
@@ -1095,12 +1095,12 @@ func (c *Conn) sendBatchExtendedWithDescription(ctx context.Context, b *Batch, d
 
 		results, err := pipeline.GetResults()
 		if err != nil {
-			return &pipelineBatchResults{ctx: ctx, conn: c, err: err}
+			return &pipelineBatchResults{ctx: ctx, conn: c, err: err, closed: true}
 		}
 
 		_, ok := results.(*pgconn.PipelineSync)
 		if !ok {
-			return &pipelineBatchResults{ctx: ctx, conn: c, err: fmt.Errorf("expected sync, got %T", results)}
+			return &pipelineBatchResults{ctx: ctx, conn: c, err: fmt.Errorf("expected sync, got %T", results), closed: true}
 		}
 	}
 
@@ -1117,7 +1117,7 @@ func (c *Conn) sendBatchExtendedWithDescription(ctx context.Context, b *Batch, d
 		if err != nil {
 			// we wrap the error so we the user can understand which query failed inside the batch
 			err = fmt.Errorf("error building query %s: %w", bi.query, err)
-			return &pipelineBatchResults{ctx: ctx, conn: c, err: err}
+			return &pipelineBatchResults{ctx: ctx, conn: c, err: err, closed: true}
 		}
 
 		if bi.sd.Name == "" {
@@ -1129,7 +1129,7 @@ func (c *Conn) sendBatchExtendedWithDescription(ctx context.Context, b *Batch, d
 
 	err := pipeline.Sync()
 	if err != nil {
-		return &pipelineBatchResults{ctx: ctx, conn: c, err: err}
+		return &pipelineBatchResults{ctx: ctx, conn: c, err: err, closed: true}
 	}
 
 	return &pipelineBatchResults{