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wire 2026-07-11
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ELIXIR FIXES TIME MATH BUG THAT ROUNDS THE WRONG WAY

By RepoJournal · Filed · About Elixir & Phoenix · Composed from the cited sources · methodology

Alexander Gubarev nseaSeb Łukasz Samson SteffenDE
4 people shipped this
Alexander Gubarev @AlexGx 2 cited nseaSeb @nseaSeb 1 cited Łukasz Samson @lukaszsamson 1 cited SteffenDE @SteffenDE

NaiveDateTime.diff/3 has been silently rounding elapsed time up instead of down, breaking its documented contract and potentially causing logic errors in any code relying on time-based calculations.

The culprit: NaiveDateTime.diff/3 was truncating each operand separately before subtracting, computing floor(t1) - floor(t2) instead of floor(t1 - t2) [1]. When the subtrahend's fractional seconds exceeded the minuend's, this flipped the rounding direction entirely. An elapsed span of 86399.5 seconds (less than one day) incorrectly returned 1 for :day. This fix restores the documented guarantee that fractional results are truncated, not rounded up. Meanwhile, Duration.from_iso8601/1 was accepting malformed ISO 8601 strings with duplicate S markers for seconds [2], a parsing bug now corrected. On the spec side, Registry.lock/3 gains its missing type signature [3], and List specs are tightened to match their actual input handling [4]. These are the kind of quiet correctness fixes that ship before someone's calendar math breaks in production.

$ ls elixir/reviews/ # the step-back reads

the week in review Comments land in the Elixir AST the month in review Elixir core tuning, Ecto breaking change, LiveView patches dominate August
Topics: Elixir & Phoenix Full archive → Weekly reviews →

Quick answers

What shipped in Elixir & Phoenix on July 11, 2026?
NaiveDateTime.diff/3 has been silently rounding elapsed time up instead of down, breaking its documented contract and potentially causing logic errors in any code relying on time-based calculations. In total, 18 commits and 17 pull requests landed.
Who contributed to Elixir & Phoenix on July 11, 2026?
4 developers shipped this update, including Alexander Gubarev, nseaSeb, Łukasz Samson, and SteffenDE.
What were the notable Elixir & Phoenix updates?
Fix `NaiveDateTime.diff/3` over-counting incomplete units, Fix Duration.from_iso8601/1 accepting duplicate S (secs) when fractional, and Add spec to Registry.lock/3 (#15575).
♥

$ log Elixir & Phoenix --recent

Elixir trims Calendar.ISO parsing and weekday math, densifies coverage accounting 6 shipped File stat functions accept open handles, Keyword.drop aligns its membership check 5 shipped phx.new templates pin a Tailwind CLI that fails on macOS, LiveView starts 1.3.0-dev 3 shipped Elixir reverts duplicate alias detection, stale test deps resolve from source records 8 shipped

$ log --all # elsewhere on the wire

@openclaw Cold-start Gateway diagnostics stop crying wolf, doctor repairs plugin drift Agentic Coding Cline desktop bundles shrink, goose unblocks its own clicks

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Rails Django Laravel Node.js Go Vercel Vue.js Kubernetes HashiCorp Arch Linux Linux Anthropic

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