fix(run): a blank script crashes pdm run --list

[VXNCXNX]

Pull Request Checklist

• A news fragment is added in news/ describing what is new. (news/3842.bugfix.md; happy to renumber it if you would rather it carried a different number)
• Test cases added for changed code. (test_run_show_list_of_scripts_with_blank_script in tests/cli/test_run.py)

Describe what you have changed in this PR.

What's broken

A blank script makes pdm run --list unusable.

[tool.pdm.scripts]
build = "python -V"
blank = "   "

$ pdm run --list
[IndexError]: list index out of range
WARNING: Add '-v' to see the detailed traceback

pdm run --json fails the same way. Everything else keeps working, including pdm run build, so a single blank entry takes out the listing for every other script in the file.

  File ".../pdm/cli/commands/run.py", line 460, in show_list
    task.short_description,
  File ".../pdm/cli/commands/run.py", line 154, in short_description
    fallback = f"{lines[0]}{termui.Emoji.ELLIPSIS}" if len(lines) > 1 else lines[0]
IndexError: list index out of range

The fix

lines is built by filtering blank lines out, so a whitespace-only script leaves it empty, and the else branch indexes lines[0] unconditionally.

The empty case now falls back to an empty description, which is what the listing needs: a row with a blank Description cell rather than no table at all.

╭───────┬──────┬─────────────╮
│ Name  │ Type │ Description │
├───────┼──────┼─────────────┤
│ blank │ cmd  │             │
│ build │ cmd  │ python -V   │
╰───────┴──────┴─────────────╯

short_description is the only accessor, and its three call sites are show_list for the table, as_json for --json, and the task display, so the one guard covers all three. --json now emits "help": "" for the blank script.

Scope

There is a second IndexError of the same family further down the file, on the composite path, reachable when {args} interpolates to nothing. That is a separate concern with a behaviour decision attached, so it is not in this PR.

Verification

test_run_show_list_of_scripts_with_blank_script, right after test_run_show_list_of_scripts, matching its style of asserting on rendered table rows. With the guard reverted it fails with the IndexError above.

tests/cli/test_run.py -k "composite or list_of_scripts" is 26 passed, against 25 on main. ruff check and ruff format are both clean.

No matching open issue was filed for this, I hit it with a whitespace-only script in my own pyproject.toml.

Disclosure: written with AI assistance (Claude Code). I reproduced the issue, ran the change and the verification myself.

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[VXNCXNX]

Good call, done. A blank script now shows <BLANK_SCRIPT> instead of an empty cell:

╭────────────┬──────┬─────────────────╮
│ test_blank │ cmd  │ <BLANK_SCRIPT>  │
│ test_cmd   │ cmd  │ flask db upgrade│
╰────────────┴──────┴─────────────────╯

The test asserts the marker rather than the empty string, so removing the branch fails it with the original IndexError rather than passing quietly. tests/cli/test_run.py is 92 passed. News fragment updated to mention the marker.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.36%. Comparing base (a50e76f) to head (0d8831d).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3842   +/-   ##
=======================================
  Coverage   88.36%   88.36%           
=======================================
  Files         121      121           
  Lines       13240    13250   +10     
  Branches     2249     2252    +3     
=======================================
+ Hits        11700    11709    +9     
+ Misses        970      969    -1     
- Partials      570      572    +2     

Flag	Coverage Δ
unittests	88.25% <100.00%> (+<0.01%)	⬆️

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[frostming]

Review: APPROVE ✅

The fix is correct, minimal, and safe to merge.

Bug

A blank/whitespace-only script (e.g. blank = " ") made pdm run --list and pdm run --json crash with IndexError: list index out of range — short_description filters blank lines, leaving lines[0] unguarded.

Fix

In Task.short_description (src/pdm/cli/commands/run.py), add a guard:

if not lines:
    fallback = "<BLANK_SCRIPT>"
else:
    fallback = ...

Single change fixes both --list and --json since both call short_description.

Verification (local)

• tests/cli/test_run.py: 92 passed (checked out PR head 0d8831d2 in a worktree)
• E2E: pdm run --list renders <BLANK_SCRIPT> for both " " and "" scripts; non-blank scripts unaffected
• --json emits "help": "<BLANK_SCRIPT>"
• Multi-line scripts still get the ellipsis (…) suffix

CI

All green: Pack + Testing matrix (3.10–3.15 × macOS/ubuntu/windows). mergeStateStatus: CLEAN, mergeable. Codecov: all modified lines covered, coverage unchanged.

Note

The reviewer suggestion (frostming) to mark it with <BLANK_SCRIPT> rather than an empty cell is implemented in the head commit, and the news fragment was updated accordingly.