Add dec and dec_length to ProgressBar

src/progress_bar.rs

@@ -235,6 +235,15 @@ impl ProgressBar {
         }
     }
 
+    /// Decrease the position of the progress bar by `delta`
+    pub fn dec(&self, delta: u64) {
+        self.pos.dec(delta);
+        let now = Instant::now();
+        if self.pos.allow(now) {
+            self.tick_inner(now);
+        }
+    }
+
     /// A quick convenience check if the progress bar is hidden
     pub fn is_hidden(&self) -> bool {
         self.state().draw_target.is_hidden()
@@ -289,6 +298,10 @@ impl ProgressBar {
     pub fn inc_length(&self, delta: u64) {
         self.state().inc_length(Instant::now(), delta);
     }
+    /// Decrease the length of the progress bar
+    pub fn dec_length(&self, delta: u64) {
+        self.state().dec_length(Instant::now(), delta);
+    }
 
     /// Sets the current prefix of the progress bar
     ///

src/state.rs

@@ -107,6 +107,13 @@ impl BarState {
         self.update_estimate_and_draw(now);
     }
 
+    pub(crate) fn dec_length(&mut self, now: Instant, delta: u64) {
+        if let Some(len) = self.state.len {
+            self.state.len = Some(len.saturating_sub(delta));
+        }
+        self.update_estimate_and_draw(now);
+    }
+
     pub(crate) fn inc_length(&mut self, now: Instant, delta: u64) {
         if let Some(len) = self.state.len {
             self.state.len = Some(len.saturating_add(delta));
@@ -585,6 +592,10 @@ impl AtomicPosition {
         self.pos.fetch_add(delta, Ordering::SeqCst);
     }
 
+    pub(crate) fn dec(&self, delta: u64) {
+        self.pos.fetch_sub(delta, Ordering::SeqCst);
+    }
+
     pub(crate) fn set(&self, pos: u64) {
         self.pos.store(pos, Ordering::Release);
     }