Read stdin via sys.stdin for cross-platform support (closes #640) by aallan · Pull Request #644 · aallan/vera

aallan · 2026-05-10T22:09:32Z

Summary

Closes #640.

_load_and_parse(path) in vera/cli.py previously handled stdin input by calling Path('/dev/stdin').read_text(). On Unix that worked because /dev/stdin is a kernel-provided special file mapping to fd 0; on Windows the path doesn't exist as a filesystem entry, so the path-based read raised FileNotFoundError and vera <subcommand> /dev/stdin failed with "Error: file not found: /dev/stdin".

Failing tests on Windows (pre-fix)

All 6 in tests/test_cli.py::TestStdinInput:

test_check_reads_source_once
test_run_dev_stdin_subprocess
test_verify_dev_stdin_subprocess
test_compile_dev_stdin_wat
test_compile_dev_stdin_default_output
test_check_dev_stdin_module_resolution

Fix

When path in _STDIN_PATHS (already a frozenset of "-" and "/dev/stdin"), read directly from sys.stdin instead of going through Path. Portable across Unix and Windows; also more semantically correct — the user's intent is "read from the process's stdin", not "read from a specific file path".

Behaviour preservation

All 7 existing TestStdinInput tests pass unchanged on Unix (the path-vs-stdin distinction was an implementation detail of the read step).
Logical path / module resolution / output naming unchanged: stdin still resolves to Path.cwd() / "stdin.vera", so vera compile /dev/stdin writes stdin.wasm in CWD and imports resolve from CWD.
- sentinel (also in _STDIN_PATHS) gets the same Windows-portable behaviour as a side benefit.

Test plan

All 7 tests in TestStdinInput pass on macOS (existing behaviour preserved)
Full pytest suite green (3,782 passed, 14 skipped)
All 6 Windows-failing tests pass on the windows-latest matrix entries once this lands (currently advisory; the count of red Windows tests should drop by 6)

Part of the #637 follow-up cluster

Sibling PRs: #643 (\U escape in test fixtures, addresses #642), and forthcoming PR for #641 (cp1252 file I/O encoding audit + drops continue-on-error + bumps version). Once all three close, the Windows entries become strict gates.

🤖 Generated with Claude Code

Summary by CodeRabbit

Bug Fixes
- Improved CLI stdin handling for portability: the tool now correctly accepts piped input (including cases previously using /dev/stdin) and normalises the logical stdin path for module resolution/output naming, resolving Windows “file not found” failures and addressing related failing stdin tests.

`_load_and_parse(path)` in `vera/cli.py` previously handled stdin input by calling `Path('/dev/stdin').read_text()`. On Unix that worked because /dev/stdin is a kernel-provided special file mapping to fd 0; on Windows the path doesn't exist as a filesystem entry, so the path-based read raised `FileNotFoundError` and `vera <subcommand> /dev/stdin` failed with "Error: file not found: /dev/stdin". Six failing tests on the post-#637 windows-latest matrix entries: `tests/test_cli.py::TestStdinInput::*`. Fix: when `path in _STDIN_PATHS` (already a frozenset of `"-"` and `"/dev/stdin"`), read directly from `sys.stdin` instead of going through Path. Portable across Unix and Windows; also more semantically correct — the user's intent is "read from the process's stdin", not "read from a specific file path". Existing 7 `TestStdinInput::*` tests pass unchanged on Unix (the path-vs-stdin distinction was an implementation detail); they should now also pass on the windows-latest matrix entries once #639's advisory CI picks this up. Module resolution and output-path defaults are unchanged: stdin still resolves to `Path.cwd() / "stdin.vera"` for the logical path, so `vera compile /dev/stdin` writes `stdin.wasm` in CWD and module imports resolve from CWD (not from `/dev/`). Closes #640. Co-Authored-By: Claude <noreply@anthropic.invalid>

coderabbitai · 2026-05-10T22:09:42Z

No actionable comments were generated in the recent review. 🎉

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CHANGELOG.md

📝 Walkthrough

Walkthrough

_load_and_parse() in vera/cli.py now detects stdin markers ("-" and "/dev/stdin") and reads source text directly from sys.stdin instead of the filesystem. The returned logical path is normalised to Path.cwd() / "stdin.vera" for portable module resolution, whilst diagnostics retain the original CLI path argument.

Changes

stdin Input Support

Layer / File(s)	Summary
Specification `vera/cli.py`	Docstring clarifies stdin detection, sys.stdin reading, and the semantic distinction between logical path (module resolution) and original path (diagnostics).
Implementation `vera/cli.py`	Conditional logic detects stdin markers and reads from `sys.stdin`; logical path normalised to CWD-relative `stdin.vera`; filesystem paths unchanged.
Changelog `CHANGELOG.md`	Added Unreleased → Fixed note for `#640` describing the stdin portability fix and closed failing stdin tests.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Possibly related issues

aallan/vera#640: This PR addresses the Windows-compatibility stdin handling problem by implementing cross-platform detection of stdin markers and direct sys.stdin reading.

Possibly related PRs

aallan/vera#411: Both PRs modify stdin handling in vera/cli.py to avoid double-reading /dev/stdin and normalise the logical path for stdin inputs.

Suggested labels

compiler, docs

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately and concisely summarises the primary change: replacing /dev/stdin file-system access with sys.stdin reading to resolve Windows portability issues, directly addressing issue `#640`.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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Commit unit tests in branch claude/issue-640-stdin-windows

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codecov · 2026-05-10T22:10:46Z

Codecov Report

❌ Patch coverage is 66.66667% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.97%. Comparing base (9c8dd83) to head (7fddb60).

Files with missing lines	Patch %	Lines
vera/cli.py	66.66%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #644      +/-   ##
==========================================
- Coverage   90.97%   90.97%   -0.01%     
==========================================
  Files          59       59              
  Lines       23134    23137       +3     
  Branches      259      259              
==========================================
+ Hits        21047    21048       +1     
- Misses       2080     2082       +2     
  Partials        7        7

Flag	Coverage Δ
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python	`94.76% <66.66%> (-0.01%)`	⬇️

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Closes the third sub-issue from PR #639's matrix-expansion follow-up cluster (#641 cp1252 file I/O encoding) and flips the Windows matrix entries from advisory to strict. This is the "now works on Windows" release. Set PYTHONUTF8=1 in the CI test job environment so Python's text-mode open() defaults to UTF-8 regardless of locale (PEP 540). Covers all CI-side encoding failures with a single config change rather than auditing ~30 individual call sites. Closes ~9 failing tests across test_codegen.py, test_codegen_monomorphize.py, test_codegen_closures.py, test_html.py. Also added explicit encoding='utf-8' to vera/parser.py's grammar load — the load-bearing site that runs on every parse, so users on Windows without PYTHONUTF8=1 in their shell still get correct grammar loading (defense-in-depth). Filed #645 for the broader audit (every text-mode open() / read_text() / write_text() call site for explicit encoding) as the durable fix. Drop continue-on-error advisory mode PR #639 added Windows entries with continue-on-error: ${{ matrix.os == 'windows-latest' }} so failures didn't block merges while #640, sub-issues now closed (PR for #642 sanitises Windows paths in test fixtures; PR for #640 reads sys.stdin cross-platform; this PR closes #641). The continue-on-error line is removed in this release; the matrix is now fully strict across all 9 entries (ubuntu / macos / windows × 3.11 / 3.12 / 3.13). Version bump 0.0.142 → 0.0.143 This is the Windows-compatibility milestone — the project went from "untested on Windows" to "Windows is a strict gate" in three sequential PRs (#643 / #644 / this). Marking with a minor version bump and "now works on Windows" framing in CHANGELOG. Co-Authored-By: Claude <noreply@anthropic.invalid>

The post-#637 Windows CI rollout (PRs #639/#643/#644/#646) hit three test-fixture footguns — `tempfile.NamedTemporaryFile`'s delete-while-open behaviour, Windows paths embedded in Vera string literals tripping the `\U` escape, and cp1252 default file I/O encoding. Each had a portable workaround. Added a "Test Fixture Conventions" section to TESTING.md (immediately before "Adding Tests") with the three rules + their canonical wrong/right code snippets. Each rule cites the test that surfaced the bug + the PR that fixed it. Added a brief "Cross-platform pitfalls" section to CLAUDE.md's project-orientation footer that points at the TESTING.md section. The CLAUDE.md entry is a one-bullet pointer per rule, not a full repeat — keeping the substantive content in TESTING.md as the single source of truth. These notes will save the next contributor (or agent) from re-discovering the same footguns. Co-Authored-By: Claude <noreply@anthropic.invalid>

aallan mentioned this pull request May 10, 2026

Windows-strict CI: cp1252 fix + drop advisory + bump to v0.0.143 #646

Merged

9 tasks

aallan added 2 commits May 10, 2026 23:23

Merge branch 'main' into claude/issue-640-stdin-windows

fcc47be

Add CHANGELOG entry for #640 stdin fix

7fddb60

aallan merged commit 6922fe6 into main May 10, 2026
19 of 22 checks passed

aallan deleted the claude/issue-640-stdin-windows branch May 10, 2026 22:30

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Read stdin via sys.stdin for cross-platform support (closes #640)#644

Read stdin via sys.stdin for cross-platform support (closes #640)#644
aallan merged 3 commits into
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claude/issue-640-stdin-windows

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Summary

Failing tests on Windows (pre-fix)

Fix

Behaviour preservation

Test plan

Part of the #637 follow-up cluster

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aallan commented May 10, 2026 •

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