changelog: 2026-04-30 digest (initial)

.watermark.json

@@ -1,6 +1,6 @@
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-  "source_repo": "phoenixframework/phoenix",
-  "last_digest_sha": "7dc2de3049eb6c3582942040ceb5d53389207ae9",
+  "source_repo": "elixir-lang/elixir",
+  "last_digest_sha": "55a3899e75efd579723da1927500b82f206329e4",
   "last_digest_at": "2026-04-30T14:01:00Z",
   "last_refresh_sha": null,
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changelog/2026-04-30.md

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-# Phoenix Digest — 2026-04-30
+# Elixir Digest — 2026-04-30
 
-## Bug Fixes
+## Type System / Gradual Typing
 
-### #6667 — Fix live_title having line breaks (lubien)
+### #15324 — Fix invalid type inference on size compare in guards
+- **Author:** lukaszsamson
+- **Merged:** 2026-04-29
+- Mirror expressions like `tuple_size(x) >= 2` and `2 <= tuple_size(x)` were producing different type inferences.
+- Fix introduces `mirror_order/1` helper that correctly flips comparison operators when operands are swapped.
+- Impact: Guards with size on the right now correctly infer the same type as left-sided equivalents.
 
-**Merged:** 2026-04-29T17:20:23Z
+### #15322 — Fix map union optimization for open maps
+- **Author:** gldubc (Guillaume Duboc)
+- **Merged:** 2026-04-29
+- Optimizer subtype shortcut incorrectly concluded open map contained by closed map when field types matched.
+- Open maps can have extra keys — fix rejects shortcut on tag (open/closed) mismatch.
+- Impact: Fixes false type narrowing with unions of open and closed map types.
 
-The `phx.new` generator template had `<.live_title>` content on separate lines.
-The HEEx formatter injected literal newlines into the rendered `<title>` tag,
-which appeared in link previews on Discord, WhatsApp, and Telegram.
+### #15319 — Fix map difference union optimization
+- **Author:** gldubc (Guillaume Duboc)
+- **Merged:** 2026-04-28
+- Disabled `:union` case of single-key open-map difference optimization.
+- Could build invalid union literals causing double negation to leave phantom empty maps.
 
-**Fix:** Collapse the template to a single line with `phx-no-format`, preventing
-the formatter from re-introducing whitespace.
+## Core / Runtime
 
-**Impact:** Every new Phoenix 1.8 project shipped this cosmetic bug. Users had
-to manually add `phx-no-format` as a workaround.
+### #15306 — Fix reentrancy of Code.eval_*
+- **Author:** lukaszsamson
+- **Merged:** 2026-04-28
+- Nested `Code.eval_string` clobbered outer eval's `dbg_callback` and `?elixir_eval_env` in process dict.
+- Fix: save/restore pattern (save before, restore in `after` block).
+- Discussion: Jonatan Kłosko caught test wasn't testing nested eval; José simplified implementation.
+- Lesson: Process dictionary as implicit state = reentrancy bugs. Deliberate trade-off for version decoupling.
 
-**Discussion:** Issue reported and PR landed same day. SteffenDE (core team)
-requested the PR, lubien delivered within the hour.
+### #15316 — Consistently return path as binary in relative_to_cwd
+- **Author:** lukaszsamson
+- **Merged:** 2026-04-28
+- `Path.relative_to_cwd/1` could return chardata on `:file.get_cwd` failure.
+- All code paths now normalize to binary.
 
-- [PR #6667](https://github.com/phoenixframework/phoenix/pull/6667)
-- [Issue #6666](https://github.com/phoenixframework/phoenix/issues/6666)
+## Patterns to Extract
 
----
-
-*Light day. One quick community fix.*
+- **Process dict save/restore for reentrancy** (#15306): When using process dict as implicit state, always save/restore in try/after to handle reentrancy. The Elixir team chose this over closures to avoid coupling eval to specific Elixir versions.
+- **Set-theoretic type system edge cases** (#15322, #15319): Open vs closed map distinction is subtle in BDD-based type representations. Subtype checks must respect structural tags, not just field types.