Fix #11: reject quoted timestamps instead of silently parsing as null

[andreabedini]

Fixes #11.

Problem

If a user writes a quoted timestamp in meta.toml:

timestamp = '2022-03-29T06:19:50+00:00'

instead of the correct bare TOML datetime:

timestamp = 2022-03-29T06:19:50+00:00

the old code silently parsed it as Nothing (because Toml.dioptional swallows all failures, not just missing-key ones). The user ended up with a broken index — no package timestamp, broken index-state support — with no error or warning.

Fix

Replaces Toml.dioptional (timeCodec "timestamp") with a handrolled optionalTimeCodec that distinguishes between:

• key absent → Nothing (fine)
• key present but wrong type → parse error (previously silently swallowed)

The underlying matchMaybe helper looks up the key first; if it's present it applies the BiMap and surfaces any type mismatch as an error. This is the approach discussed in the tomland issue and previously explored in #57.

The error message users now see is clear and actionable:

BiMap error in key 'timestamp': Invalid constructor
  * Expected: TZoned
  * Actual:   Text "2022-03-29T06:19:50+00:00"

Changes

• app/Foliage/Meta.hs: add optionalTimeCodec + matchMaybe, use in sourceMetaCodec
• foliage.cabal: add mtl, unordered-containers (needed by the new codec)
• tests/Tests.hs: new test case verifying foliage build fails on a quoted timestamp
• tests/fixtures/bad-timestamp/: minimal fixture for the new test

[Copilot]

Pull request overview

This PR addresses quoted TOML timestamps being silently treated as missing metadata, so invalid meta.toml files fail instead of producing repositories without package timestamps.

Changes:

• Adds a custom optional timestamp codec that distinguishes missing keys from type mismatches.
• Adds a regression test and fixture for quoted timestamp rejection.
• Updates executable dependencies and root-only ignore patterns for generated directories.

Reviewed changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
app/Foliage/Meta.hs	Replaces optional timestamp parsing with a custom codec that errors on invalid timestamp values.
tests/Tests.hs	Adds a build-failure regression test for quoted timestamps.
tests/fixtures/bad-timestamp/_sources/pkg-a/1.0.0.0/meta.toml	Adds an invalid quoted timestamp fixture.
foliage.cabal	Adds dependencies required by the custom codec implementation.
.gitignore	Attempts to anchor generated directory ignore patterns to the repository root.

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[neilmayhew]

Sorry, I didn't see the review request until now. I'll take a look tomorrow.

[neilmayhew]

Nice to have this fixed!

[neilmayhew]

Suggested change

	result <- try @SomeException (callCommand "foliage build --no-signatures")
	result <- try @IOError (callCommand "foliage build --no-signatures")

Pedantic, I know, but SomeException always looks like a code smell to me,

Even better would be to use readProcessWithExitCode and check the exit code, and maybe even the stderr, but that's a lot of trouble for not a lot of gain.

[neilmayhew]

I forgot about auto-merge being enabled!

Oh, well, it was fine anyway.