Hacktoberfest 2026: the issues maintainers tagged for October, open and beginner-friendly. Browse Hacktoberfest issues

Formatter collapses unequal legal indentation levels and emits unparseable source

Open
#1,246 0 comments 0 reactions 0 assignees View on GitHub

Maintainers usually reply within 1 day

Nobody has claimed this yet.

Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
74/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
c
Domain
compilers

Research direction

Start with src/fmt.c:352–382 and docs/SPEC.md:69, then run the supplied indent.eigs commands after a fresh default make build. Exercise the reproducer and the listed unequal-increment, sibling, dedent, and 2-/4-space cases; done means formatted programs remain parseable, preserve execution output, and satisfy the stated regression checks.

Written by the indexing model from the issue text.

Description

area:lint-tooling bug found-by:code-review

Formatting a valid nested block can collapse two different indentation levels and make the program fail to parse. --fmt returns success; --fmt --write would replace the working source with that result. The LSP formatting handler uses the same formatter.

Reproduction

Save this as indent.eigs. The two indented lines use four and six spaces, respectively:

if 1:
    if 1:
      print of 7
print of 9
eigenscript indent.eigs
eigenscript --fmt indent.eigs > formatted.eigs
eigenscript formatted.eigs

Original: exit 0, stdout 7\n9\n. Formatter: exit 0, but emits:

if 1:
    if 1:
    print of 7
print of 9

The result exits 1 with Parse error line 3:5: expected indent, got identifier ('print').

Cause and contract

docs/SPEC.md:69 requires consistent indentation within a block, not equal increments between blocks. The original program executes successfully.

src/fmt.c:352–382 finds the smallest positive indentation (4 here), then computes level = indents[i] / min_indent. Integer division maps both 4 and 6 to depth 1. Formatting needs to preserve the actual nesting/dedent structure instead of deriving it from one global width.

Regression acceptance

  • Formatting the reproducer preserves successful execution and its exact output.
  • Cover unequal indentation increments, sibling blocks, dedents, and ordinary 2-/4-space inputs.
  • Assert parseability and output after applying the formatter; idempotence alone cannot detect this corruption.

Distinct from #729/#750, which address splitting operators and keeping the operator table synchronized.

Verification

Confirmed with a fresh default make build of b91768e23c5a874a64e76e4af9ab291e6aa49983 in a clean isolated worktree. The original, formatter, and transformed program were executed separately with inherited EIGS_* variables removed; exit status and output were captured for each.

Dominant language
C
Stars
3
Forks
7
Avg merge
3h 56m
Merged PRs (30d)
102

Getting set up

Open in Codespaces

Starts the project's dev container in your browser, under your own GitHub account.

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

More from InauguralSystems/EigenScript

All issues in InauguralSystems/EigenScript

Similar issues

More C issues

Get new issues in your inbox

A short digest of beginner-friendly GitHub issues.