trees: show its phases as N of M, with progress, elapsed time and ETA (closes #113)

trees now runs in four phases, open, read, group and write, each under
the progress display scan uses, from the line naming the database to
the summary line. open covers a wait on a busy database. read counts
the records first, as scan's load does, then reads them against that
count; group counts the directories, and write the groups. The display
gains a unit so that each rate names what its phase counts; every scan
phase passes files and prints as before. The tests that pinned trees'
stderr now allow the phase lines between the database line and the
summary.

Judgement call: opening the database is a phase of its own, so there are four phases, not the three the issue sketches.
Judgement call: the count and the read are separate queries, as in scan's load, so during a scan the read can end slightly past or short of its total.

Model: opus-5-5

progress_test.go

@@ -86,30 +86,44 @@ func TestProgressLine(t *testing.T) {
 		},
 		want: "[1/5] load: counting the records, elapsed 10s, eta unknown",
 	}, {
-		p:    &progress{label: scanPhase("hash"), total: 100, count: 20},
+		p: &progress{
+			label: scanPhase("hash"), unit: scanUnit, total: 100, count: 20,
+		},
 		want: "[3/5] hash: [20/100] 20%, 2 files/s, elapsed 10s, eta 40s",
 	}, {
-		p:    &progress{label: scanPhase("hash"), total: 100},
+		p:    &progress{label: scanPhase("hash"), unit: scanUnit, total: 100},
 		want: "[3/5] hash: [0/100] 0%, 0 files/s, elapsed 10s, eta unknown",
 	}, {
-		p:    &progress{label: scanPhase("update"), total: 0},
+		p:    &progress{label: scanPhase("update"), unit: scanUnit, total: 0},
 		want: "[4/5] update: [0/0] 100%, 0 files/s, elapsed 10s, eta 0s",
 	}, {
 		p: &progress{
-			label: scanPhase("walk"), total: 100, estimate: true, count: 20,
+			label: scanPhase("walk"), unit: scanUnit, total: 100,
+			estimate: true, count: 20,
 		},
 		want: "[2/5] walk: [20/~100] 20%, 2 files/s, elapsed 10s, eta 40s",
 	}, {
 		// Past the estimate the walk cannot tell how long it has left.
 		p: &progress{
-			label: scanPhase("walk"), total: 100, estimate: true, count: 120,
+			label: scanPhase("walk"), unit: scanUnit, total: 100,
+			estimate: true, count: 120,
 		},
 		want: "[2/5] walk: [120/~100] 120%, 12 files/s, elapsed 10s, " +
 			"eta unknown",
 	}, {
 		// A first scan's walk has no estimate.
-		p:    &progress{label: scanPhase("walk"), total: -1, count: 20},
+		p: &progress{
+			label: scanPhase("walk"), unit: scanUnit, total: -1, count: 20,
+		},
 		want: "[2/5] walk: 20 files, 2 files/s, elapsed 10s, eta unknown",
+	}, {
+		// The rate is in what the phase counts.
+		p: &progress{
+			label: treesPhase("group"), unit: "directories", total: 100,
+			count: 20,
+		},
+		want: "[3/4] group: [20/100] 20%, 2 directories/s, elapsed 10s, " +
+			"eta 40s",
 	}}
 
 	for _, tc := range cases {
@@ -129,7 +143,7 @@ func TestLineFitsRoom(t *testing.T) {
 
 	ago := time.Now().Add(-10 * time.Second)
 	hash := &progress{
-		label: scanPhase("hash"), total: 100, count: 20,
+		label: scanPhase("hash"), unit: scanUnit, total: 100, count: 20,
 		start: ago, rateStart: ago,
 	}
 	content := &progress{
@@ -183,7 +197,8 @@ func TestSetTotalStartsRate(t *testing.T) {
 
 	waited := time.Now().Add(-20 * time.Second)
 	p := &progress{
-		label: scanPhase("load"), total: -1, start: waited, rateStart: waited,
+		label: scanPhase("load"), unit: scanUnit, total: -1, start: waited,
+		rateStart: waited,
 	}
 
 	p.setTotal(100)
@@ -226,7 +241,9 @@ func awaitOutput(t *testing.T, stderr func() string, want string,
 //nolint:paralleltest // captureStderr replaces the process-wide os.Stderr
 func TestPlainProgressPrintsAtStartAndEnd(t *testing.T) {
 	stderr := captureStderr(t)
-	p := newProgress(progressParams{label: scanPhase("hash"), total: 1000})
+	p := newProgress(progressParams{
+		label: scanPhase("hash"), unit: scanUnit, total: 1000,
+	})
 
 	for range 1000 {
 		p.increment()
@@ -289,8 +306,14 @@ func TestTerminalRedrawsWhileWaiting(t *testing.T) {
 		params progressParams
 		want   string // how the line shows a count of 50
 	}{
-		{progressParams{label: scanPhase("walk"), total: -1}, "50 files,"},
-		{progressParams{label: scanPhase("hash"), total: 100}, "[50/100],"},
+		{
+			progressParams{label: scanPhase("walk"), unit: scanUnit, total: -1},
+			"50 files,",
+		},
+		{
+			progressParams{label: scanPhase("hash"), unit: scanUnit, total: 100},
+			"[50/100],",
+		},
 	}
 
 	for _, tc := range cases {
@@ -341,8 +364,9 @@ func drawLate(stderr func() string, params progressParams, width int,
 }
 
 // TestTerminalLinesKeepETA checks the line each display shows on an
-// 80-column terminal at a large scan's counts and times: the rate is
-// left out, so that the elapsed time and the ETA stay whole.
+// 80-column terminal at a large scan's counts and times, and the line
+// of trees' read phase at the same counts: the rate is left out, so
+// that the elapsed time and the ETA stay whole.
 //
 //nolint:paralleltest // captureStderr replaces the process-wide os.Stderr
 func TestTerminalLinesKeepETA(t *testing.T) {
@@ -354,18 +378,29 @@ func TestTerminalLinesKeepETA(t *testing.T) {
 	}{{
 		// Past its estimate, the walk cannot tell how long it has left.
 		params: progressParams{
-			label: scanPhase("walk"), total: 1200000, estimate: true,
+			label: scanPhase("walk"), unit: scanUnit, total: 1200000,
+			estimate: true,
 		},
 		want: "[2/5] walk: [1234567/~1200000] 103%, elapsed 2h30m0s, " +
 			"eta unknown",
 	}, {
-		params: progressParams{label: scanPhase("hash"), total: 9876543},
+		params: progressParams{
+			label: scanPhase("hash"), unit: scanUnit, total: 9876543,
+		},
 		want: "[3/5] hash: [1234567/9876543] 12%, elapsed 2h30m0s, " +
 			"eta 17h30m0s",
 	}, {
-		params: progressParams{label: scanPhase("content"), total: 9876543},
+		params: progressParams{
+			label: scanPhase("content"), unit: scanUnit, total: 9876543,
+		},
 		want: "[5/5] content: [1234567/9876543] 12%, elapsed 2h30m0s, " +
 			"eta 17h30m0s",
+	}, {
+		params: progressParams{
+			label: treesPhase("read"), unit: "records", total: 9876543,
+		},
+		want: "[2/4] read: [1234567/9876543] 12%, elapsed 2h30m0s, " +
+			"eta 17h30m0s",
 	}}
 
 	for _, tc := range cases {
@@ -389,7 +424,9 @@ func TestTerminalLinesFitWidth(t *testing.T) {
 
 	for _, width := range []int{120, 100, 80, 72, 60, 50, 40} {
 		for _, total := range []int64{9876543, 20000} {
-			params := progressParams{label: scanPhase("content"), total: total}
+			params := progressParams{
+				label: scanPhase("content"), unit: scanUnit, total: total,
+			}
 			out := drawLate(stderr, params, width, total/8)
 
 			if width == 120 && !strings.Contains(out, "% |") {
@@ -426,8 +463,16 @@ func TestTerminalNarrowedRedrawsInPlace(t *testing.T) {
 		params progressParams
 		narrow int
 	}{
-		{progressParams{label: scanPhase("walk"), total: -1}, 60},
-		{progressParams{label: scanPhase("hash"), total: 9876543}, 90},
+		{
+			progressParams{label: scanPhase("walk"), unit: scanUnit, total: -1},
+			60,
+		},
+		{
+			progressParams{
+				label: scanPhase("hash"), unit: scanUnit, total: 9876543,
+			},
+			90,
+		},
 	}
 
 	for _, tc := range cases {