Compute critical path when ninja finishes

Keep a running map of the critical path to each edge as it
finishes.  At the end of the build, find the edge with the
longest critical path and print the path to out/soong.log.

Test: critical_path_test.go
Change-Id: Ie01d26b068b768156b166bff00cdc3273e8124ca
diff --git a/ui/status/critical_path_test.go b/ui/status/critical_path_test.go
new file mode 100644
index 0000000..965e0ad
--- /dev/null
+++ b/ui/status/critical_path_test.go
@@ -0,0 +1,166 @@
+// Copyright 2019 Google Inc. All rights reserved.
+//
+// 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 status
+
+import (
+	"reflect"
+	"testing"
+	"time"
+)
+
+type testCriticalPath struct {
+	*criticalPath
+	Counts
+
+	actions map[int]*Action
+}
+
+type testClock time.Time
+
+func (t testClock) Now() time.Time { return time.Time(t) }
+
+func (t *testCriticalPath) start(id int, startTime time.Duration, outputs, inputs []string) {
+	t.clock = testClock(time.Unix(0, 0).Add(startTime))
+	action := &Action{
+		Description: outputs[0],
+		Outputs:     outputs,
+		Inputs:      inputs,
+	}
+
+	t.actions[id] = action
+	t.StartAction(action, t.Counts)
+}
+
+func (t *testCriticalPath) finish(id int, endTime time.Duration) {
+	t.clock = testClock(time.Unix(0, 0).Add(endTime))
+	t.FinishAction(ActionResult{
+		Action: t.actions[id],
+	}, t.Counts)
+}
+
+func TestCriticalPath(t *testing.T) {
+	tests := []struct {
+		name     string
+		msgs     func(*testCriticalPath)
+		want     []string
+		wantTime time.Duration
+	}{
+		{
+			name: "empty",
+			msgs: func(cp *testCriticalPath) {},
+		},
+		{
+			name: "duplicate",
+			msgs: func(cp *testCriticalPath) {
+				cp.start(0, 0, []string{"a"}, nil)
+				cp.start(1, 0, []string{"a"}, nil)
+				cp.finish(0, 1000)
+				cp.finish(0, 2000)
+			},
+			want:     []string{"a"},
+			wantTime: 1000,
+		},
+		{
+			name: "linear",
+			//  a
+			//  |
+			//  b
+			//  |
+			//  c
+			msgs: func(cp *testCriticalPath) {
+				cp.start(0, 0, []string{"a"}, nil)
+				cp.finish(0, 1000)
+				cp.start(1, 1000, []string{"b"}, []string{"a"})
+				cp.finish(1, 2000)
+				cp.start(2, 3000, []string{"c"}, []string{"b"})
+				cp.finish(2, 4000)
+			},
+			want:     []string{"c", "b", "a"},
+			wantTime: 3000,
+		},
+		{
+			name: "diamond",
+			//  a
+			//  |\
+			//  b c
+			//  |/
+			//  d
+			msgs: func(cp *testCriticalPath) {
+				cp.start(0, 0, []string{"a"}, nil)
+				cp.finish(0, 1000)
+				cp.start(1, 1000, []string{"b"}, []string{"a"})
+				cp.start(2, 1000, []string{"c"}, []string{"a"})
+				cp.finish(1, 2000)
+				cp.finish(2, 3000)
+				cp.start(3, 3000, []string{"d"}, []string{"b", "c"})
+				cp.finish(3, 4000)
+			},
+			want:     []string{"d", "c", "a"},
+			wantTime: 4000,
+		},
+		{
+			name: "multiple",
+			//  a d
+			//  | |
+			//  b e
+			//  |
+			//  c
+			msgs: func(cp *testCriticalPath) {
+				cp.start(0, 0, []string{"a"}, nil)
+				cp.start(3, 0, []string{"d"}, nil)
+				cp.finish(0, 1000)
+				cp.finish(3, 1000)
+				cp.start(1, 1000, []string{"b"}, []string{"a"})
+				cp.start(4, 1000, []string{"e"}, []string{"d"})
+				cp.finish(1, 2000)
+				cp.start(2, 2000, []string{"c"}, []string{"b"})
+				cp.finish(2, 3000)
+				cp.finish(4, 4000)
+
+			},
+			want:     []string{"e", "d"},
+			wantTime: 4000,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			cp := &testCriticalPath{
+				criticalPath: NewCriticalPath(nil).(*criticalPath),
+				actions:      make(map[int]*Action),
+			}
+
+			tt.msgs(cp)
+
+			criticalPath := cp.criticalPath.criticalPath()
+
+			var descs []string
+			for _, x := range criticalPath {
+				descs = append(descs, x.action.Description)
+			}
+
+			if !reflect.DeepEqual(descs, tt.want) {
+				t.Errorf("criticalPath.criticalPath() = %v, want %v", descs, tt.want)
+			}
+
+			var gotTime time.Duration
+			if len(criticalPath) > 0 {
+				gotTime = criticalPath[0].cumulativeDuration
+			}
+			if gotTime != tt.wantTime {
+				t.Errorf("cumulativeDuration[0].cumulativeDuration = %v, want %v", gotTime, tt.wantTime)
+			}
+		})
+	}
+}