<!--
  SPDX-License-Identifier: Apache-2.0
  SPDX-FileCopyrightText: 2020 The Gleam contributors
-->

# Changelog

## v1.15.0 - 2026-03-16

- Fixed a bug where the language server wouldn't show the correct hover for some
  patterns.
  ([Giacomo Cavalieri](https://github.com/giacomocavalieri))

## v1.15.0-rc2 - 2026-03-16

### Bug fixes

- Marked the `bitSize` and `bitOffset` fields of `BitArray$BitArray` TypeScript
  definition as optional.
  ([acandoo](https://github.com/acandoo))

- Fixed invalid JavaScript code generation when ints or floats had prefixed `0`s
  before and after an `_` (e.g. `000_001`).
  ([Gavin Morrow](https://github.com/gavinmorrow))

## v1.15.0-rc1 - 2026-03-04

### Compiler

- The compiler now reports an error when int and float binary operators are
  used incorrectly in case expression guards.
  ([Adi Salimgereyev](https://github.com/abs0luty))

- The compiler now supports string concatenation in clause guards:

  ```gleam
  case message {
    #(version, action) if version <> ":" <> action == "v1:delete" ->
      handle_delete()
    _ -> ignore()
  }
  ```

  ([Adi Salimgereyev](https://github.com/abs0luty))

- Improved the code generated on the Erlang target when dividing a `Float`
  number by the literal number `0.0`.
  ([Giacomo Cavalieri](https://github.com/giacomocavalieri))

- The compiler no longer shows the structure of internal types when displaying
  an "Inexhaustive patterns" error, making it harder to inadvertently rely on
  internal implementation details.
  ([Giacomo Cavalieri](https://github.com/giacomocavalieri))

- The JavaScript prelude TypeScript API now contains the `BitArray$isBitArray`
  and `BitArray$BitArray$data` functions.
  ([Louis Pilfold](https://github.com/lpil))

- The type-checking JavaScript functions for Gleam data structure now use the
  `value is TypeName` TypeScript return type rather than `boolean`.
  ([Louis Pilfold](https://github.com/lpil))

- The compiler now shows better error message on passing unexpected labeled
  arguments by taking into account, whether it's a function or a constructor.
  ([Andrey Kozhev](https://github.com/ankddev))

### Build tool

- Upgraded `actions/checkout` from v4 to v6 in the GitHub Actions workflow used
  by `gleam new`.
  ([Christian Widlund](https://github.com/chrillep))

- When adding a package that does not exist on Hex, the message is a bit
  friendlier.
  ([Ameen Radwan](https://github.com/Acepie))

- The `gleam.toml` format is now consistent. The two sausage-case fields
  (`dev-dependencies` and `tag-prefix`) have been replaced by snake_case
  versions. Files using the old names will continue to work.
  ([Louis Pilfold](https://github.com/lpil))

- The password used for encrypting new local Hex API keys must now be at least
  8 characters in length.
  ([Louis Pilfold](https://github.com/lpil))

- The `gleam help add`, `gleam help deps`, and `gleam help docs` commands have
  been improved with much more detailed documentation output.
  ([Louis Pilfold](https://github.com/lpil))

- When attempting to publish a package on Hex with an already taken name,
  the message is clearer.
  ([vyacheslavhere](https://github.com/vyacheslavhere))

- The build tool will now refuse to publish any package that has the default
  README generated by the `gleam new` command.
  ([Giacomo Cavalieri](https://github.com/giacomocavalieri))

- The build tool now uses OAuth and time-based one-time-passwords for
  authentication with Hex, improving security.
  Any legacy API tokens previously stored will be revoked after authenticating
  using OAuth.
  ([Louis Pilfold](https://github.com/lpil))

- The build tool will now refuse to publish any package that has no README, or
  an empty README.
  ([Giacomo Cavalieri](https://github.com/giacomocavalieri))

### Language server

- The language server now allows extracting the start of a pipeline into a
  variable.
  ([Giacomo Cavalieri](https://github.com/giacomocavalieri))

- The language server now shows hover information when hovering over custom type
  definitions.
  ([Giacomo Cavalieri](https://github.com/giacomocavalieri))

- The language server now shows hover information when hovering over a custom
  type's constructors.
  ([Giacomo Cavalieri](https://github.com/giacomocavalieri))

- The language server is now smarter when producing autocompletions. Imagine
  you're updating your code to fully qualify the uses of the `Json` type:

  ```gleam
  pub fn payload() -> js|Json
  //                    ^ typing the module name
  ```

  Accepting the `json.Json` completion will now produce the correct `json.Json`
  annotation rather than generating invalid code: `json.JsonJson`.
  ([Giacomo Cavalieri](https://github.com/giacomocavalieri))

- The language server now suggests completions for keywords like `echo`,
  `panic`, and `todo`.
  ([Giacomo Cavalieri](https://github.com/giacomocavalieri))

- The "Add missing patterns" code action will insert a catch all pattern for
  internal types, making it harder to inadvertently rely on internal
  implementation details.
  ([Giacomo Cavalieri](https://github.com/giacomocavalieri))

- The language server will no longer show completions for the fields of internal
  types outside the module they're defined in, making it harder to inadvertently
  rely on internal implementation details.
  ([Giacomo Cavalieri](https://github.com/giacomocavalieri))

- The language server now suggests a quick-fix code action for when a custom type
  definition uses a type parameter in its variants that have not been declared in
  its header.
  ([Andi Pabst](https://github.com/andipabst))

- The `Extract function` code action now provides more ergonomic/idiomatic
  refactorings when used on anonymous functions.
  ([Hari Mohan](https://github.com/seafoamteal))

- It's now possible to find references and rename variables in string prefix
  patterns.

  ```gleam
  case wibble {
    "1" as digit <> rest -> digit <> rest
    //     ^^^^^    ^^^^
    // You can now trigger "Find references" and "Rename" from here
  }
  ```

  ([Igor Castejón](https://github.com/IgorCastejon))

- The language server now offers a rename for module when the cursor is placed
  over its import statement or when placed on its name or alias somewhere. For
  example,

  ```gleam
  import lustre/element
  import lustre/element/html
  import lustre/event

  fn view(model: Int) -> element.Element(Msg) {
    //                     ^  Renaming module to `el` here
    let count = int.to_string(model)

    html.div([], [
      html.button([event.on_click(Incr)], [element.text(" + ")]),
      html.p([], [element.text(count)]),
      html.button([event.on_click(Decr)], [element.text(" - ")]),
    ])
  }
  ```

  Using renaming when hovering on module name will would result in the
  following code:

  ```gleam
  import lustre/element as el
  import lustre/element/html
  import lustre/event

  fn view(model: Int) -> el.Element(Msg) {
    let count = int.to_string(model)

    html.div([], [
      html.button([event.on_click(Incr)], [el.text(" + ")]),
      html.p([], [el.text(count)]),
      html.button([event.on_click(Decr)], [el.text(" - ")]),
    ])
  }
  ```

  ([Vladislav Shakitskiy](https://github.com/vshakitskiy))

- The "Fill labels" code action now uses variables from scope when they match
  the label name and expected type, using shorthand syntax (`name:`) instead of
  `name: todo`.

  ([Vladislav Shakitskiy](https://github.com/vshakitskiy))

- The "Interpolate String" code action now lets the user "cut out" any portion
  of a string, regardless of whether it is a valid Gleam identifier or not.
  ([Hari Mohan](https://github.com/seafoamteal))

- When interpolating an expression at the very start or the very end
  of a string, redundant empty strings are no longer added before/after the
  interpolated expression.
  ([Hari Mohan](https://github.com/seafoamteal))

- The language server now performs best-effort zero value generation for
  `decode.failure` when using the `Generate Dynamic Decoder` code action.
  ([Hari Mohan](https://github.com/seafoamteal))

- The `Generate Dynamic Decoder` and `Generate To-JSON Function` code action
  now generate a decoder and an encoder, respectively, for `Nil` values.
  ([Hari Mohan](https://github.com/seafoamteal))

- The language server now supports renaming, go to definition, hover, and
  finding references from expressions in case clause guards.
  ([Surya Rose](https://github.com/GearsDatapacks))

- The language server now supports `textDocument/foldingRange`, enabling
  folding for contiguous import blocks and multiline top-level definitions such
  as function bodies, custom types, constants, and type aliases.

  For example, this import block:

  ```gleam
  import gleam/int
  import gleam/list
  import gleam/string
  ```

  can now be folded in the editor to:

  ```gleam
  import gleam/int ...
  ```

  ([Aayush Tripathi](https://github.com/aayush-tripathi))

- The function signature helper now displays original function definition
  generic names when arguments are unbound. For example, in this code:

  ```gleam
  pub fn wibble(x: something, y: fn() -> something, z: anything) { Nil }

  pub fn main() {
      wibble( )
          // ↑
  }
  ```

  will show a signature help

  ```gleam
  wibble(something, fn() -> something, anything)

  ```

  instead of

  ```gleam
  wibble(a, fn() -> a, b) -> Nil
  ```

  ([Samuel Cristobal](https://github.com/scristobal))

### Formatter

- The formatter no longer wraps multiple tuple or field access into a block.
  ([Giacomo Cavalieri](https://github.com/giacomocavalieri))

### Bug fixes

- The compiler now emits correctly-scoped JavaScript code for `case` expressions
  whose subjects directly match one of the branches.
  ([Justin Lubin](https://github.com/justinlubin))

- Fixed a bug where some bit array patterns would erroneously be marked as
  unreachable.
  ([Giacomo Cavalieri](https://github.com/giacomocavalieri))

- Fixed a bug where the Gleam standard library's `dict.each` function would
  incorrectly be assumed to be pure.
  ([Giacomo Cavalieri](https://github.com/giacomocavalieri))

- The compiler now correctly tracks the minimum required version for constant
  record updates to be `>= 1.14.0`.
  ([Giacomo Cavalieri](https://github.com/giacomocavalieri))

- The compiler now correctly tracks the minimum required version for
  expressions in `BitArray`s' `size` option to be `>= 1.12.0`.
  ([Giacomo Cavalieri](https://github.com/giacomocavalieri))

- Fixed a bug where the formatter would not properly format some function calls
  if the last argument was followed by a trailing comment.
  ([Giacomo Cavalieri](https://github.com/giacomocavalieri))

- Fixed a bug where the compiler would generate invalid code on the JavaScript
  target when using a `case` expression as the right hand side of an equality
  check in an `assert`.
  ([Giacomo Cavalieri](https://github.com/giacomocavalieri))

- Fixed a bug where the compiler would generate invalid code on the JavaScript
  target for some `case` expressions using clause guards.
  ([Giacomo Cavalieri](https://github.com/giacomocavalieri))

- The formatter no longer stack overflows trying to format lists with many
  items.
  ([Giacomo Cavalieri](https://github.com/giacomocavalieri))

- Fixed a bug where the formatter would not be able to consistently format a
  constant list with an `@internal` attribute.
  ([Giacomo Cavalieri](https://github.com/giacomocavalieri))

- The "convert to pipe" code action now works on nested function calls as well,
  rather than always being applied to the outermost one.
  ([Giacomo Cavalieri](https://github.com/giacomocavalieri))

- Fixed a bug where the compiler would not detect and reject duplicate modules
  in a project's dependencies.
  ([Giacomo Cavalieri](https://github.com/giacomocavalieri))

- The language server no longer shows completions when typing a number.
  ([Giacomo Cavalieri](https://github.com/giacomocavalieri))

- The language server no longer recommends the deprecated `@target` attribute.
  ([Hari Mohan](https://github.com/seafoamteal))

- The compiler no longer crashes when trying to pattern match on a
  `UtfCodepoint`.
  ([Hari Mohan](https://github.com/seafoamteal))

- Fixed a bug that would result in not being able to rename an aliased pattern.
  ([Giacomo Cavalieri](https://github.com/giacomocavalieri))

- Fixed JavaScript codegen bug for `assert` when using `&&` with comparison
  operators on the right side.
  ([vyacheslavhere](https://github.com/vyacheslavhere))

- Added an error message when attempting to update packages that are not
  dependencies of the project, instead of failing silently.
  ([Etienne Boutet](https://github.com/EtienneBoutet),
  [Vladislav Shakitskiy](https://github.com/vshakitskiy))

- The build tool now doesn't perform code generation when exporting package
  interface.
  ([Andrey Kozhev](https://github.com/ankddev))

- The "Extract constant" code action now correctly places new constant when
  function has documentation. For example,

  ```gleam
  /// Wibble does some wobbling
  pub fn wibble() {
    let x = "wobble"
    //  ^ Trigger "Extract constant" here
    x
  }
  ```

  Previously, it would incorrectly place it below doc comment:

  ```gleam
  /// Wibble does some wobbling
  const x = "wobble"

  pub fn wibble() {
    x
  }
  ```

  Now it will correctly place constant above doc comment:

  ```gleam
  const x = "wobble"

  /// Wibble does some wobbling
  pub fn wibble() {
    x
  }
  ```

  ([Andrey Kozhev](https://github.com/ankddev))

- Fixed a bug where renaming would not work properly if there was an error in
  target file.
  ([Surya Rose](https://github.com/GearsDatapacks))

- Fixed a bug where generics in custom types would not be properly generated
  when emitting TypeScript declarations.
  ([Surya Rose](https://github.com/GearsDatapacks))

- Fixed a bug where dev dependencies would be compiled and included in
  production builds such as `gleam export erlang-shipment`.
  ([John Downey](https://github.com/jtdowney))

- Fixed a bug where the package cache would not properly be reset when a version
  of a package was replaced on Hex.
  ([Surya Rose](https://github.com/GearsDatapacks))

- Fixed a crash (`bad_generator`) that could occur when a linked OTP process
  exits with a non-standard exit reason.
  ([John Downey](https://github.com/jtdowney))

- Fixed a bug where diagnostic about incorrect `size` and `unit` options would
  use incorrect error location.
  ([Andrey Kozhev](https://github.com/ankddev))

- `gleam add` now adds correct constraints for pre-release versions.
  ([Andrey Kozhev](https://github.com/ankddev))

- Fixed a bug where changes to a path dependency's own dependencies were not
  detected when rebuilding the root project, causing the compiler to report
  errors about missing modules.
  ([daniellionel01](https://github.com/daniellionel01))

- Fixed a bug where the compiler would crash when type-checking record
  updates if the constructor definition has a positional field defined after
  labelled fields.
  ([Hari Mohan](https://gituhub.com/seafoamteal))