tools: Add the 'cts merge' sub-command

Merges results files into one.

Bug: dawn:1342
Change-Id: Ia241afc982c88c840a102abba211053611f77f5b
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/88441
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>

tools/src/cmd/cts/main.go

@@ -29,6 +29,7 @@ import (
 
 	// Register sub-commands
 	_ "dawn.googlesource.com/dawn/tools/src/cmd/cts/format"
+	_ "dawn.googlesource.com/dawn/tools/src/cmd/cts/merge"
 	_ "dawn.googlesource.com/dawn/tools/src/cmd/cts/results"
 	_ "dawn.googlesource.com/dawn/tools/src/cmd/cts/time"
 )

tools/src/cmd/cts/merge/merge.go

@@ -0,0 +1,76 @@
+// Copyright 2022 The Dawn Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package merge
+
+import (
+	"context"
+	"flag"
+	"fmt"
+	"os"
+
+	"dawn.googlesource.com/dawn/tools/src/cmd/cts/common"
+	"dawn.googlesource.com/dawn/tools/src/cts/result"
+)
+
+func init() {
+	common.Register(&cmd{})
+}
+
+type cmd struct {
+	flags struct {
+		output string
+	}
+}
+
+func (cmd) Name() string { return "merge" }
+
+func (cmd) Desc() string { return "merges results files into one" }
+
+func (c *cmd) RegisterFlags(ctx context.Context, cfg common.Config) ([]string, error) {
+	flag.StringVar(&c.flags.output, "o", "results.txt", "output file. '-' writes to stdout")
+	return []string{"first-results.txt", "second-results.txt ..."}, nil
+}
+
+func (c *cmd) Run(ctx context.Context, cfg common.Config) error {
+	// Load each of the results files and merge together
+	var results result.List
+	for _, path := range flag.Args() {
+		// Load results
+		r, err := result.Load(path)
+		if err != nil {
+			return fmt.Errorf("while reading '%v': %w", path, err)
+		}
+		// Combine and merge
+		if len(results) > 0 {
+			results = result.Merge(results, r)
+		} else {
+			results = r
+		}
+	}
+
+	// Open output file
+	output := os.Stdout
+	if c.flags.output != "-" {
+		var err error
+		output, err = os.Create(c.flags.output)
+		if err != nil {
+			return fmt.Errorf("failed to open output file '%v': %w", c.flags.output, err)
+		}
+		defer output.Close()
+	}
+
+	// Write out
+	return result.Write(output, results)
+}