GUI: fix invisible text on Linux, tiny button hit-areas, missing labels.

Found by running and debugging the Linux build on a virtual display:

- impl_linux.go: set fontSize (16, like Darwin). It was only defined
  for the Android and Darwin builds, so on Linux every label and
  button was rendered at size zero (all text invisible).
- ui.go: extend the Button click area to the full button width, not
  just the label width. Short labels (e.g. a few characters in a
  full-width list row) had a tiny tap target that was easy to miss.
- main.go: set Color: black on the insert-page buttons (<, >, generate,
  @, #). A zero-value NRGBA has A=0 (transparent), so their labels
  were invisible even though the buttons worked.
- main.go: gofmt (modern operator spacing).

cmd/passgo-gui/impl_linux.go

@@ -12,6 +12,10 @@ var (
 	noidLabelText = "No GPG ids available"
 )
 
+func init() {
+	fontSize = 16
+}
+
 func getConfDir() (string, error) {
 	ret, err := app.DataDir()
 	if err != nil {

cmd/passgo-gui/main.go

@@ -651,17 +651,17 @@ func eventLoop() {
 
 	var insName, insValue string
 	genBtn := &SelButton{SelColor: gray}
-	genBtn.Button = Button{Size: unit.Sp(fontSize), Label: "generate"}
+	genBtn.Button = Button{Size: unit.Sp(fontSize), Label: "generate", Color: black}
 	symBtn := &SelButton{SelColor: gray}
 	numBtn := &SelButton{SelColor: gray}
-	symBtn.Button = Button{Size: unit.Sp(fontSize), Label: "@"}
-	numBtn.Button = Button{Size: unit.Sp(fontSize), Label: "#"}
+	symBtn.Button = Button{Size: unit.Sp(fontSize), Label: "@", Color: black}
+	numBtn.Button = Button{Size: unit.Sp(fontSize), Label: "#", Color: black}
 	symBtn.Select()
 	numBtn.Select()
 	lenEd := &widget.Editor{SingleLine: true, Alignment: text.End}
 	lenEd.SetText("15")
-	lBtn := &Button{Size: unit.Sp(fontSize), Label: "<", Background: gray}
-	rBtn := &Button{Size: unit.Sp(fontSize), Label: ">", Background: gray}
+	lBtn := &Button{Size: unit.Sp(fontSize), Label: "<", Color: black, Background: gray}
+	rBtn := &Button{Size: unit.Sp(fontSize), Label: ">", Color: black, Background: gray}
 
 	updatePw := func() {
 		if !genBtn.Selected {

cmd/passgo-gui/ui.go

@@ -89,8 +89,14 @@ func (b *Button) Layout(gtx C) D {
 			ret := ins.Layout(gtx, func(gtx C) D {
 				return l.Layout(gtx)
 			})
-			// Register the click handler for the label area.
-			stk := clip.Rect(image.Rectangle{Max: ret.Size}).Push(gtx.Ops)
+			// Register the click handler for the whole button area, not
+			// just the label: otherwise buttons with short labels (in
+			// full-width rows, for example) have a tiny tap target.
+			hit := ret.Size
+			if hit.X < gtx.Constraints.Max.X {
+				hit.X = gtx.Constraints.Max.X
+			}
+			stk := clip.Rect(image.Rectangle{Max: hit}).Push(gtx.Ops)
 			event.Op(gtx.Ops, b)
 			b.Click.Add(gtx.Ops)
 			stk.Pop()

main.go

@@ -63,9 +63,9 @@ func GetStore(store *Store) error {
 	}
 	for i := len(id) - 1; i > 0; i-- {
 		if id[i] == '>' {
-			for j := i-1; j > 0; j-- {
+			for j := i - 1; j > 0; j-- {
 				if id[j] == '<' {
-					id = id[j+1:i]
+					id = id[j+1 : i]
 				}
 			}
 			break