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 :)

nandi (Jan 12 2026 at 17:14):

Changelog (January 5-12, 2026)

Bug Fixes

Type System

• Fix Str type Error (#9003)
• Fix type checking for recursive functions with type annotations (#8979)
• Fix type store and regions out of sync in checkPlatformRequirements (#8994)
• Fix stack overflow with recursive nominal type unification (#8931)
• Fix type alias lookup for platform requirements (#8916)
• Fix check reqs rank mismatch (#8995)
• Remove implicit structural-to-nominal type conversion for method calls (#8939)

Compiler Crashes

• Fix crash when calling float literal as function (#8941)
• Fix crash on recursive closures with nested pattern matching (#8933)
• Fix panic on empty match expression (#8932)
• Fix stack overflow with self-referential variable definitions (#8942, #8943)
• Fix NotNumeric crash when closures capture for-loop elements (#8946)

Memory Management

• Fix Box.unbox memory leak for boxes passed through FFI (#8981)
• Fix memory leak when ? operator causes early return in for loop (#8944)
• Fix memory corruption in error messages when using ? on non-Try types (#8947)
• Fix incref alignment check for recursive tag unions with pointer tagging (#8978)
• Fix tag_union decref with nested layout mismatch (#8754)

Pattern Matching

• Fix wrong exhaustiveness error for match on tuple with list and wildcard (#8924)
• Fix non-exhaustive list pattern not catching empty list case (#8935)

Formatter

• Fix formatter dropping platform header targets section (#8989)
• Fix formatter instability with open tag union blank lines (#8927)

Parser

• Fix minus operator parsing without spaces in function calls (#8930)

Layouts

• Fix record extension causing duplicate fields in layout (#8991)

Interpreter

• Fix instantiation in interpreter
• Fix interpreter bugs in hosted lambda handling (#8928)
• Fix static dispatch effect bug
• Store identifiers in e_anno_only to fix cross-module hosted functions

REPL & Playground

• Fix REPL snapshot for record field ordering
• Fix playground underline (#8956)
• Wasm playground fixes (#8952)

New Features

Compiler

• Detect infinite while loops at compile time
• Move circular definition detection from runtime to compile-time (#8923)

Cross-Compilation

• Support platform-bundled macOS sysroots for cross-compilation (#8983)

Standard Library Helpers

• Add toWholeInt/fromWholeInt helpers to RocDec (#8966)
• Add readAligned/writeChecked helpers to reduce integer handling boilerplate (#8964)

Interpreter Improvements

• Add asRocList() and setRocList() methods to StackValue (#8955)
• Improve StackValue RocStr methods for idiomatic Zig (#8954)
• Improve asClosure() and add box lifecycle helpers to StackValue (#8958)

Code Quality

Refactoring

• Centralize allocation in Check
• Move extra strings allocation to problem store
• Extract selectCopyFallbackFn to deduplicate copy function selection (#8963)
• Preserve type annotation on err
• Don't generalize top-level after every def + fix instantiation

Cleanup

• Remove unused ExtraStringIdx import
• Remove unused current_block_statements field
• Remove dead createTagUnionLayout function

Test Improvements

• Add tests demonstrating correct host layout for entry point arguments
• Convert fx tests to cheaper eval/type-checking tests
• Add regression tests for various issues
• Fix eval test syntax: use strings instead of deprecated i64 suffix

CI/Infrastructure

• Avoid flaky nix timeout
• Skip kcov coverage on Linux x86_64 (#8961)
• Fix nightly macOS ld64 library not found (#8951)
• Increase Tidy limit to 1.5MB

Dependencies

• Bump @remix-run/router and react-router-dom in checkmate/www (#8957)
• Bump react-router and react-router-dom in checkmate/www (#8965)

nandi (Jan 19 2026 at 17:47):

Roc Changelog - Week of January 12-19, 2026

Summary

This week saw major improvements to the LSP (Language Server Protocol) implementation, significant work on the dev backend with JIT code generation, and several important bug fixes.

Highlights

:fixing: Bug Fixes

• Bool.False displaying as 0 (#9051) - Fixed issue where Str.inspect(Bool.False) would show "0" instead of "False" when the Bool value was extracted from a polymorphic opaque type through a method call.

• List literal panic in polymorphic for loops (#8905) - Fixed panic when creating list literals inside polymorphic for loops.

• Record builder map2 chaining (#9035) - Fixed record builder to properly chain map2 calls.

• roc run target flag (#9008) - Fixed roc run to respect --target flag and use platform's default target.

• roc run non-platform packages (#9030) - Fixed roc run to support non-platform packages in IPC mode.

• Memory leaks - Fixed slow memory leak from accumulating constant string arenas and WASM interpreter memory leak in long-running applications.

LSP Improvements

Major LSP enhancements for a better editor experience:

New Features

• Document formatting - Wire the Roc formatter to handle textDocument/formatting requests
• Document symbols - Show function and variable definitions in editor outline/breadcrumbs
• Folding ranges - Enable code folding for records, lists, and grouped expressions
• Selection ranges - Semantic selection expansion (Ctrl+Shift+Right) for syntactic structures
• Document highlight - Scope-aware highlighting of variable references (handles shadowing correctly)
• Goto definition for types - Navigate to type definitions in annotations (e.g., clicking Str in x : Str)
• Cross-module semantic tokens - Distinguish Module.function calls from record.field access
• Dependency graph - Track module relationships and content hashes for incremental builds
• Exports hash tracking - Foundation for smarter cache invalidation

Bug Fixes

• Fix goto definition for local types and nested type annotations
• Fix goto definition for builtin module lookups like U64.to_str
• Fix hover on type annotation lines
• Fix document symbols to match correct module by file path
• Fix selection range hierarchy to walk AST properly
• Preserve content hashes across dependency graph rebuilds
• Fix memory leak in Report allocations

Dev Backend / JIT

Significant progress on the development backend with JIT code generation:

• JIT infrastructure - Add dev backend JIT infrastructure with numeric evaluation
• Binary operations - Add binary operation and unary minus code generation
• Control flow - Add if/else expression code generation
• Functions - Add function/lambda expression support
• Data structures - Add record, tuple, list, block, string, and tag expression support
• Record access - Add dot-access handling for record field access
• For loops - Implement e_for and e_low_level_lambda support
• Compile-time evaluation - Add comptime_value.zig for compile-time evaluation
• Cross-compilation - Fix cross-compilation issues for JIT and ELF
• Windows support - Fix x86_64 Windows calling convention and VirtualAlloc error handling

Code Quality / Refactoring

• Typed payloads migration - Major refactor replacing generic extra_data field with typed payload unions for type-safe data access
• Typed lists - Migrate pattern_list, index arrays, statements, diagnostics, and more to typed storage
• Remove dead code - Remove separator comments and unused imports per linter rules

CI / Build

• Add build release step
• More general retry logic for CI
• Only run nix CI when needed
• Retry on UnknownHostName errors

Pull Requests Merged

Fabian Schmalzried (Jan 20 2026 at 14:37):

Was there a decision to have a (jitted?) dev backend instead of/in addition to the interpreter?

Anton (Jan 20 2026 at 14:39):

Not jitted yet, but yes dev backend in addition to the interpreter

Luke Boswell (Jan 20 2026 at 19:30):

My understanding is that the JIT stuff is purely an intermediate or internal implementation detail so we can compare the current interpreter against the backends that they evaluate to the same thing to support thier development side by side. I think sometime in the future if the dev backends are good enough we might be able to retire the interpreter and cut out a lot of complexity/duplication.

nandi (Jan 26 2026 at 22:03):

Changelog: January 19 - January 26, 2026

:fixing: Build System & Multi-threading

PR #9072 - Fix Sibling Modules (Luke Boswell)

A major overhaul of the build pipeline:

• Migrate roc build to use BuildEnv/Coordinator pipeline (2f032392ea)
• Add actor model for multi-threaded compilation (0386fb6817)
• Add --jobs flag for roc check with cache tracing telemetry (fd0e946e22)
• Unify cache checking for single and multi-threaded builds (7eadaa6520)
• Fix platform path resolution for apps in subdirectories (1100efcf24)
• Fix allocator mismatch in multi-threaded coordinator cleanup (e2bae59c28)
• Fix cache to recursively load sibling module imports (554bb086b3)
• Rename trace-cache to trace-build (3a3dc89ade)
• Fix cache deserialization for mutable types (1dccbc0b6c)
• Add --verbose to build with improved cache statistics (90cb41640c)
• Remove legacy GlobalQueue build pipeline (368f31d07a)
• Unify roc run IPC path with Coordinator (e3b80581e7)
• Enable hosted transform for roc build (fa8887e757)

PR #9085 - Fix Benchmarks Exit 137 (Anton-4)

• Reduce macOS shared memory to 8GB and fix munmap cleanup (2e14acf18c)

:bug: Bug Fixes

PR #9077 - Number Literal Static Dispatch Fix (Dan Knutson, Jared Ramirez)

• Avoid null error on number literal static dispatch (45ab6b683a)
• Instantiate static dispatch methods from other modules (a74f825973)
• Track constraint origin for static dispatch errors (294b078f9f)

PR #9066 - Fix Cache Panic (Anton-4)

• Fix cache incompatibility between debug and release builds (f06e1b684e) - The module cache now includes build mode in version string to prevent crashes from mismatched struct layouts

PR #9063 - Fix Issue #9043 (Richard Feldman)

• Fix self-reference detection for tuple patterns with var elements (8e6c099aaa) - Fixes crash on (_, var $n) = f($n)

PR #9061 - Fix Issue #9056 (Richard Feldman)

• Fix formatter dropping module qualifiers in imports (bef18d6853) - import a.B.C was incorrectly formatted as import a.C
• Fix handling of imports without qualifiers (2d83d64ca7)

PR #9038 - Fix Issue #9034 (Richard Feldman)

• Fix roc check to resolve platform-exposed module types in annotations

:high_voltage: REPL Improvements (Yanni Papandreou)

PR #9081 - REPL Enhancements

• Got basic ReplLine working (48f92ea961)
• Added basic history support (f929aba34d)
• Added cancel line command (c8ade7cf06)
• Added TTY detection and top-level doc comments (2c9695f05d)
• First attempt at Windows support (f0a4c8939b, 8e40f98dbd, 8f77870dbc)

:broom: Code Quality & Refactoring (Jared Ramirez)

PR #9065 - Unify Improvements

• Remove types store snapshotting from unify (9ec0945b72)
• Remove early unification pattern (5a77ceac60)
• Remove unsound nominal backing type merges (4d62d52c64)
• Remove marks (41da1d14b6)
• Unify whole function, not arg-by-arg and ret (45755f70e3)

PR #9045 - Improve Recursion & Early Return Errors

• Improve expected Try type error message (8b61f97ef4)
• Make ? desugar to explicitly nominal Try constructors (26a5444034)
• Remove lambda tracking in favor of deferred constraints (4cc17676ee)
• Move early return logic tracking to Can (8e07a2c525)
• Remove decl_gen (835b9af51a)
• Improve self recursive error message (e01456934a)

:silhouettes: Contributors This Week

• Luke Boswell - Build system & multi-threading
• Jared Ramirez - Type system & unification improvements
• Richard Feldman - Bug fixes for formatter and self-reference detection
• Anton-4 - Cache fixes and macOS memory improvements
• Yanni Papandreou - REPL improvements and Windows support
• Dan Knutson - Static dispatch fixes

Total commits: ~80  
Merged PRs: #9085, #9081, #9077, #9076, #9072, #9066, #9065, #9063, #9061, #9045, #9038

nandi (Feb 02 2026 at 17:37):

Roc Changelog (Jan 26 - Feb 2, 2026)

:sparkles: New Features

• ?? operator - Implement double question operator (e88b26f7) - Luke Boswell
• Tuple access - Dot notation for tuple elements (#9073) (e23827316b) - Luke Boswell
• RefcountContext helpers & Info types for layout extraction - Luke Boswell
• Cross-compile: Thread RocTarget through compilation pipeline (3d6f7ac7d7) - Luke Boswell

Error Messages

• Recursion, record update, record access error messages - Jared Ramirez
• Intelligent hints & improved type module validation - Jared Ramirez, Luke Boswell

:bug: Bug Fixes

Crashes

• Segfault when ? on non-Try type (#9118) (c3fc86a24d) - Luke Boswell
• Panic on tuple access to non-tuple (8402740aac) - Luke Boswell
• NotNumeric crash with rigid type vars (538a90dab1) - Luke Boswell
• Alignment panic on 64-bit cross-compile (28fb15f73e) - Luke Boswell
• Compiler panic with concrete platform type in where clause (847bb54f7f) - Luke Boswell

Type System

• Type variable rigidity in closures (#9129) (392f77debe) - Luke Boswell
• Wildcard match on open tag unions (e716d9da65) - Luke Boswell

Coordinator/Imports

• Infinite loop on external import parse failure (3d985fba8d) - Luke Boswell
• Infinite loop on invalid package shorthand (ce83e481ab) - Luke Boswell
• Package-qualified import errors not displayed (bf3d3a8801) - Luke Boswell
• Cross-file nested module access (#9074) (f76de03baf) - Luke Boswell

WASM/Interpreter

• WASM allocator size tracking (d70145a28b) - Luke Boswell
• wasm32 struct layout (f22a429661) - Luke Boswell
• Interpreter Shim Target layout (347ed2539d) - Luke Boswell
• Hosted effects on opaque types (3ac7dc2ef7) - Luke Boswell
• Memory leaks in enableRuntimeInserts (5fcbb73b28) - Luke Boswell

Formatting

• Type annotation trailing commas, import spacing, field access after local dispatch - Luke Boswell

:books: Documentation

• ?? operator, tuple, loops, modules, static dispatch, types in langref - Luke Boswell
• is_eq, plus, minus, times, to_inspect in langref - Luke Boswell
• Roc Targets docs, mini-tutorial resources, AFL++ fuzzing docs - Luke Boswell, Anton-4

:fixing: Internal

• Migrate list ops to RefcountContext helpers - Luke Boswell
• Migrate ptrCast patterns to semantic helpers - Luke Boswell  
• Centralize unification calls, separate problems & reportings - Jared Ramirez
• Snapshot diffs, diff checker cleanup - Jared Ramirez
• Tracy logging, typos CLI tool - Jared Ramirez
• CI: flaky retry, hyperfine, triggers - Anton-4
• While loop demo - Anton-4

:silhouettes: Contributors

Anton-4 · Jared Ramirez · Luke Boswell

nandi (Feb 10 2026 at 04:43):

Roc changelog (main) — Feb 2 to Feb 9, 2026

Compiler backends

• #9161 WebAssembly backend merge and follow-up fixes (Contributor: Richard Feldman)
• #9068 more-dev-backend expansion (Contributor: Luke Boswell)
• #9145 fix for issue 9143 (Contributor: Luke Boswell)
• #9148 Windows ARM64/debug backend work (Contributor: Luke Boswell)
• #9134 dev-objects (Contributor: Richard Feldman)
• #9164 dev backend fixes (Contributor: Richard Feldman)

Type system / monomorphization / canonicalization

• #9152 improve mono pipeline (Contributor: Richard Feldman)
• #9155 alias type hashing fix (Contributor: Richard Feldman)
• #9156 tag union substitution fix (Contributor: Richard Feldman)
• #9157 closure-capture duplication fix (Contributor: Richard Feldman)
• #9159 remove unused region tracking (Contributor: Richard Feldman)
• #9160 optimize pending specialization lookup (Contributor: Richard Feldman)

Parsing / API consistency

• #9141 parse-result API unification (Contributor: Luke Boswell)
• #9142 canonicalization API unification (Contributor: Luke Boswell)

Testing / CI / benchmarks

• #9130 test coordinator updates (Contributor: Luke Boswell)
• #9150 targeted fix branch merge (Contributor: Anton-4)
• #9151 all-syntax test improvements (Contributor: Anton-4)
• #9146 remove snapshot benchmarks (Contributor: Anton-4)
• #9100 enable real benches (Contributor: Anton-4)

Docs

• #9136 reorganize docs folder (Contributor: Anton-4)
• #9137 mini tutorial updates (Contributor: Anton-4)

Dependencies

• #9138 bump bytes (Contributor: dependabot[bot])
• #9158 bump webpack (Contributor: dependabot[bot])
• #9067 bump lodash (Contributor: dependabot[bot])

Last updated: Feb 20 2026 at 12:27 UTC