Reveal the build's commit hash in place of the reset label while a finger holds the top-right corner, and dev where go run left no stamp

main.go

@@ -737,6 +737,7 @@ func run(aName, bName string, nsPerM float64) error {
 			if disp.holdReset(x, y, down, now) {
 				start = resetAll(dirs, stats)
 			}
+			disp.showVersion = down && disp.versionSpot.contains(x, y)
 			for i, d := range dirs {
 				views[i] = d.displayView()
 			}

ui.go

@@ -3,6 +3,7 @@ package main
 import (
 	"fmt"
 	"math"
+	"runtime/debug"
 	"time"
 )
 
@@ -41,6 +42,8 @@ const (
 	btnH         = 80
 	holdDuration = time.Second
 
+	versionSpotSide = 200
+
 	chipRadius = spaceTight
 	chipBorder = 2
 
@@ -72,6 +75,10 @@ type display struct {
 	holdStart  time.Time
 	holdFrac   float64
 	fired      bool
+
+	version     string
+	versionSpot rect
+	showVersion bool
 }
 
 func newDisplay() (*display, error) {
@@ -79,7 +86,7 @@ func newDisplay() (*display, error) {
 	if err != nil {
 		return nil, err
 	}
-	d := &display{fb: fb}
+	d := &display{fb: fb, version: buildVersion()}
 	for _, spec := range []struct {
 		dst  **textFace
 		bold bool
@@ -130,6 +137,7 @@ func newDisplay() (*display, error) {
 		w: btnW,
 		h: btnH,
 	}
+	d.versionSpot = rect{fb.w - versionSpotSide, 0, versionSpotSide, versionSpotSide}
 	return d, nil
 }
 
@@ -188,14 +196,17 @@ func (d *display) drawResetButton() {
 		split += w
 	}
 
-	label := "RESET"
+	label, base := "RESET", uiCyan
+	if d.showVersion {
+		label, base = d.version, uiDim
+	}
 	lx := r.x + (r.w-len(label)*d.gridB.cellW)/2
 	ly := r.y + (r.h-d.gridB.lineH)/2 - d.gridB.capTop
 	// The label straddles the fill, so each glyph takes the colour that reads
 	// against whatever is behind it.
 	for i, c := range label {
 		gx := lx + i*d.gridB.cellW
-		col := uiCyan
+		col := base
 		if gx+d.gridB.cellW/2 < split {
 			col = uiBg
 		}
@@ -203,6 +214,34 @@ func (d *display) drawResetButton() {
 	}
 }
 
+// go run never stamps VCS info, so dev builds have no revision to show.
+func buildVersion() string {
+	info, ok := debug.ReadBuildInfo()
+	if !ok {
+		return "dev"
+	}
+	var rev string
+	var dirty bool
+	for _, s := range info.Settings {
+		switch s.Key {
+		case "vcs.revision":
+			rev = s.Value
+		case "vcs.modified":
+			dirty = s.Value == "true"
+		}
+	}
+	if rev == "" {
+		return "dev"
+	}
+	if len(rev) > 9 {
+		rev = rev[:9]
+	}
+	if dirty {
+		rev += "+"
+	}
+	return rev
+}
+
 func (d *display) close() {
 	d.fb.close()
 }