Stream: compiler development

Topic: this week in roc

nandi (Dec 29 2025 at 00:39):

Nobody asked for this but decided to make a markdown of the last weeks commits from main

Roc Weekly - December 22-29, 2025

Bug Fixes

Memory & Stability

• Fixed memory corruption in unifySharedTags due to slice invalidation
• Applied same fix to unifySharedFields for extensible records
• Fixed stack overflow in tag union layout computation (#8750)
• Fixed early return value stack corruption in interpreter
• Fixed integer overflow in List operations with tuples containing strings
• Fixed integer overflow in serialization for large addresses

Parser & Tokenizer

• Fixed parse crash with malformed imports
• Fixed parse crash with where clauses
• Fixed tokenize crash with unicode escapes

Type System

• Fixed TypeMismatch when pattern matching on polymorphic function results
• Fixed infinite type detection in unification
• Fixed opaque type pattern matching in same module
• Fixed Box.unbox type resolution with records containing numeric literals (#8765)
• Fixed occurs check recursing into constraints
• Fixed value restriction for annotation-only function declarations
• Fixed discriminant ordering for tag unions with large payloads (#8773)

List Operations

• Fixed List.map crash on empty lists
• Fixed list append for empty records
• Fixed handling of list_of_zst (zero-sized types)

Other Fixes

• Fixed roc fmt inserting space between ## in doc comments
• Fixed pattern matching crash for tag unions with tuple payloads
• Fixed closure capture ident translation (#8727)
• Fixed crash when updating var through tuple destructuring in while loop
• Fixed runtime type propagation (#8646)
• Fixed tag_union handling in decrefLayoutPtr to fix memory leak
• Fixed roc_std sizes, dealloc must be manually managed by host

New Features

• break keyword - Added break statement support (#8717)
• Effectful map functions - Added effectful versions of map_ok and map_err (#8736)
• List.sum - Added List.sum method with default constraint
• Range functions - Added to and until range functions for all non-float number types

Refactoring & Improvements

• Migrated roc_std to new architecture
• Converted fx tests to eval snapshot tests for faster execution
• Value restriction refactor - only generalize lambda definitions
• Added static dispatch for binops
• Improved type printing with line breaks and Pair(a, b) syntax
• Increased Rank size from u4 to u8 to support deeper nesting
• Added heuristics for type store initial capacity
• Added combined layoutSizeAlign function for efficiency
• Removed unused functions and redundant code

Documentation

• Split langref/collections.md into separate files
• Improved platform requirements error messages
• Expanded language reference documentation
• Refined doc comment detection to require ## followed by space

Luke Boswell (Dec 29 2025 at 01:09):

Yeah lot's of progress in many areas. Roc is definitely moving fast.

Richard Feldman (Dec 29 2025 at 01:14):

"Move fast and fix things" :grinning_face_with_smiling_eyes:

Luke Boswell (Dec 29 2025 at 01:14):

Definitely not breaking things over here... :sweat_smile:

nandi (Jan 05 2026 at 18:01):

Roc Repository - Weekly Commit Summary

Period: December 29, 2025 - January 5, 2026

Summary by Category

Bug Fixes

• Recursive type handling: Fixed infinite recursion in layout size computation, tag layout mismatch causing memory corruption, crashes with recursive nominal types
• Compiler fixes: Fixed dynamic discriminant offset in comptime_evaluator, correct tag order for mkTagUnion, UNUSED VALUE error for method calls
• Parser/Formatter: Fixed formatter idempotence issues for local dispatch, chained zero-arg applications, and field access
• Memory issues: Fixed dangling slice causing index out of bounds panic (#8913), invalid free panic in non-exhaustive match errors, index out of bounds in closure decref
• Number handling: Fixed invalid number literal suffix errors, MONO output defaulting to Dec, method call return type for dbg on extracted Ok values
• Fixed crash with recursive nominal type when one variant has no payload (#8901)
• Fixed panic on multiple expects with annotated function (#8897)
• Fixed segfault with recursive nominal types in Box containers (#8816)
• Fixed dbg on U8 extracted from Ok (#8555)

New Features

• Automatic cache invalidation via compile-time struct hashing
• Migrated to RocTry instead of RocResult in roc_std_new
• Deprecated old numeric suffix syntax (e.g., 123u64) in favor of typed suffix syntax

CI/Infrastructure

• Extensive work on kcov coverage: moved between Linux/macOS, fixed DWARF5 issues, added include patterns
• Added network error patterns to flaky-retry for CI stability
• Coverage enforcement improvements and threshold adjustments
• Reverted "smarter nix CI" (#8881)

Refactoring

• Use Blake3 for version hash, removed duplicated code
• Simplified header validation in fromMappedMemory
• Converted multiple fx tests to eval/layout unit tests for better test isolation

Documentation

• Updated implementation completion status and CI results
• Deleted outdated planning docs
• Changed 'should' to 'must' in statement error messages

Anton (Jan 05 2026 at 18:07):

Thanks @nandi :)

Last updated: Jan 12 2026 at 12:19 UTC