Fix: Empty output from HelpFormatter.write_usage for a program without arguments

The Bug

Repo: pallets/click Issue: #3360 Status: PR-submitted PR: https://github.com/pallets/click/pull/3433

Description: Empty output from HelpFormatter.write_usage for a program without arguments

Fix scope: 4 lines changed in src/click/formatting.py

The Fix

This is a simple fix. The change is minimal and targeted — only what’s needed.

@@ -157,6 +157,10 @@ def write_usage(self, prog: str, args: str = "", prefix: str | None = None) -> N
         usage_prefix = f"{prefix:>{self.current_indent}}{prog} "
         text_width = self.width - self.current_indent

+        if not args:
+            self.write(f"{prefix:>{self.current_indent}}{prog}\n")
+            return
+
         if text_width >= (term_len(usage_prefix) + 20):
             # The arguments will fit to the right of the prefix.

What This Teaches

Edge cases in CLI output formatting are easy to miss because they only trigger when a specific input condition is met — in this case, an empty arguments string.

The fix adds an early return before the formatting logic, which assumes args is non-empty.

Pattern: When formatting code assumes non-empty input, add a guard clause for the empty case.

Transfer Potential

Would reading this post help fix a similar bug in another repo?

Medium — empty-input edge cases are universal, but the specific formatting pattern is CLI-tool specific. The guard clause pattern transfers to any language.

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Auto-generated from PR #3360. View all patches on GitHub.