feat(bar): Add support for custom icons

You can super a textual.renderable.bar.Bar class and change `HALF_BAR_LEFT`, `BAR`, and `HALF_BAR_RIGHT`, before passing the class as an keyword argument in the textual.widgets.ProgressBar widget as `bar_renderable`.
The keyword arg's name is weird, I'm not sure what to name it

Author: NSPC911

src/textual/renderables/bar.py

@@ -18,6 +18,10 @@ class Bar:
         gradient: Optional gradient object.
     """
 
+    HALF_BAR_LEFT: str = "╺"
+    BAR: str = "━"
+    HALF_BAR_RIGHT: str = "╸"
+
     def __init__(
         self,
         highlight_range: tuple[float, float] = (0, 0),
@@ -40,10 +44,6 @@ def __rich_console__(
         highlight_style = console.get_style(self.highlight_style)
         background_style = console.get_style(self.background_style)
 
-        half_bar_right = "╸"
-        half_bar_left = "╺"
-        bar = "━"
-
         width = self.width or options.max_width
         start, end = self.highlight_range
 
@@ -53,7 +53,7 @@ def __rich_console__(
         output_bar = Text("", end="")
 
         if start == end == 0 or end < 0 or start > end:
-            output_bar.append(Text(bar * width, style=background_style, end=""))
+            output_bar.append(Text(self.BAR * width, style=background_style, end=""))
             yield output_bar
             return
 
@@ -67,34 +67,40 @@ def __rich_console__(
 
         # Initial non-highlighted portion of bar
         output_bar.append(
-            Text(bar * (int(start - 0.5)), style=background_style, end="")
+            Text(self.BAR * (int(start - 0.5)), style=background_style, end="")
         )
         if not half_start and start > 0:
-            output_bar.append(Text(half_bar_right, style=background_style, end=""))
+            output_bar.append(Text(self.HALF_BAR_RIGHT, style=background_style, end=""))
 
         highlight_bar = Text("", end="")
         # The highlighted portion
         bar_width = int(end) - int(start)
         if half_start:
             highlight_bar.append(
                 Text(
-                    half_bar_left + bar * (bar_width - 1), style=highlight_style, end=""
+                    self.HALF_BAR_LEFT + self.BAR * (bar_width - 1),
+                    style=highlight_style,
+                    end="",
                 )
             )
         else:
-            highlight_bar.append(Text(bar * bar_width, style=highlight_style, end=""))
+            highlight_bar.append(
+                Text(self.BAR * bar_width, style=highlight_style, end="")
+            )
         if half_end:
-            highlight_bar.append(Text(half_bar_right, style=highlight_style, end=""))
+            highlight_bar.append(
+                Text(self.HALF_BAR_RIGHT, style=highlight_style, end="")
+            )
 
         if self.gradient is not None:
             _apply_gradient(highlight_bar, self.gradient, width)
         output_bar.append(highlight_bar)
 
         # The non-highlighted tail
         if not half_end and end - width != 0:
-            output_bar.append(Text(half_bar_left, style=background_style, end=""))
+            output_bar.append(Text(self.HALF_BAR_LEFT, style=background_style, end=""))
         output_bar.append(
-            Text(bar * (int(width) - int(end) - 1), style=background_style, end="")
+            Text(self.BAR * (int(width) - int(end) - 1), style=background_style, end="")
         )
 
         # Fire actions when certain ranges are clicked (e.g. for tabs)

src/textual/widgets/_progress_bar.py

@@ -72,11 +72,13 @@ def __init__(
         disabled: bool = False,
         clock: Clock | None = None,
         gradient: Gradient | None = None,
+        bar_renderable: BarRenderable = BarRenderable,
     ):
         """Create a bar for a [`ProgressBar`][textual.widgets.ProgressBar]."""
         self._clock = (clock or Clock()).clone()
         super().__init__(name=name, id=id, classes=classes, disabled=disabled)
         self.set_reactive(Bar.gradient, gradient)
+        self.bar_renderable = bar_renderable
 
     def _validate_percentage(self, percentage: float | None) -> float | None:
         """Avoid updating the bar, if the percentage increase is too small to render."""
@@ -104,7 +106,7 @@ def render(self) -> RenderResult:
                 if self.percentage < 1
                 else self.get_component_rich_style("bar--complete")
             )
-            return BarRenderable(
+            return self.bar_renderable(
                 highlight_range=(0, self.size.width * self.percentage),
                 highlight_style=Style.from_color(bar_style.color),
                 background_style=Style.from_color(bar_style.bgcolor),
@@ -133,7 +135,7 @@ def render_indeterminate(self) -> RenderResult:
             end = start + highlighted_bar_width
 
         bar_style = self.get_component_rich_style("bar--indeterminate")
-        return BarRenderable(
+        return self.bar_renderable(
             highlight_range=(max(0, start), min(end, width)),
             highlight_style=Style.from_color(bar_style.color),
             background_style=Style.from_color(bar_style.bgcolor),
@@ -226,6 +228,9 @@ class ProgressBar(Widget, can_focus=False):
     gradient: reactive[Gradient | None] = reactive(None)
     """Optional gradient object (will replace CSS styling in bar)."""
 
+    BAR_RENDERABLE: BarRenderable = BarRenderable
+    """Optional BarRenderable class for custom ProgressBar icons."""
+
     def __init__(
         self,
         total: float | None = None,
@@ -283,7 +288,7 @@ def on_mount(self) -> None:
     def compose(self) -> ComposeResult:
         if self.show_bar:
             yield (
-                Bar(id="bar", clock=self._clock)
+                Bar(id="bar", clock=self._clock, bar_renderable=self.BAR_RENDERABLE)
                 .data_bind(ProgressBar.percentage)
                 .data_bind(ProgressBar.gradient)
             )