Converting Existing Specs to Single Active Preview

Converting a spec with multiple preview versions into a spec with a single, latest preview version is complex because the changes that occur in any preview version are carried over into the next version by default. This means that each versioning decorator referencing a preview version must be dealt with in order to end with the correct decoration.

For each type decorated with a versioning decorator that references a preview version, follow these steps. If the type is decorated with more than one instance of a versioning decorator referencing different preview versions, each of these must be processed in version order (earliest version first)

A conversion consists of the following steps, outlined in the sections below

• Normalizing version decoration (optional)
• Determining which versions should be removed: this should include all preview api-versions except the last version (if the last version is a preview, that version will not be removed.)
• Handling each versioning decorator application that references a deleted preview version (except the first version)
• Removing the first version (if it is a preview)
• Removing the deleted preview versions from the Versions enum
• If there is a remaining preview version, it should be the last version in the versions enum. Ensure it is decorated with the @previewVersion decorator.
• Cleaning up (optional)

In this document we use the notation @<decorator>(T, u, [arg]) this indicates an instance of the decorator <decorator> decorating type T using version u in a set of monotonically increasing versions 1..n

Normalizing Version Decoration (optional)

Normalizing version decoration consists of removing redundant decorators and follows a few rules, described below. For these rules, consider an ordered set of versions 1...n.

• Trim any sequence of @removed decorators without an @added between them: A decorator @removed(T, c) with type T and c in 1..n may be safely removed if there is another decorator @removed(T, a) with a in 1..n and a < c unless there is a decorator @added(T, b) with b in 1..n and a < b < c.
• Trim any sequence of @added decorators without any @removed between them: A decorator @added(T, c) with type T and c in 1..n may be safely removed if there is another decorator @added(T,a) with a in 1..n and a < c unless there is a decorator @removed(T,b) with b in 1..n and a < b < c.
• Any duplicated application of a versioning decorator to a type with the same parameters may be safely removed, that is:
  • @added(T, a) and @added(T, a) can be simplified to @added(T, a)
  • @removed(T, a) and @removed(T, a) can be simplified to @removed(T, a)
  • @madeOptional(T, a) and @madeOptional(T, a) can be simplified to @madeOptional(T, a)
  • @renamedFrom(T, a, name) and @renamedFrom(T, a, name) can be simplified to @renamedFrom(T, a, name)
  • @typeChangedFrom(T, a, U) and @typeChangedFrom(T, a, U) can be simplified to @typeChangedFrom(T, a, U)
  • @returnTypeChangedFrom(T, a, U) and @returnTypeChangedFrom(T, a, U) can be simplified to @returnTypeChangedFrom(T, a, U)
• If @added(T, a) and @removed(T,a) occur, @added(T, a) may be removed.
• If any versioning decorator with 3 arguments @dec(T, v, a) where T is a type, v is a version and a is a valid arg value occurs with another application of the same decorator @dec(T, v, b) and b != a, then the innermost of the two decorators can be removed.
• If any of the following decorators reference the first version, they may be removed:
  • @added
  • @renamedFrom
  • @madeOptional
  • @typeChangedFrom
  • @returnTypeChangedFrom
• if @removed(T, 1) occurs, where T is the decorated type and 1 is the first version:
  • If T occurs in any subsequent version (i.e. if there is any), this decorator should remain
  • Otherwise, the decorated type can simply be removed.

Handling Each Versioning Decorator That References a Preview Version

@renamedFrom(T, u, name) decorator

• Based on the version referenced in the decorator, determine the immediate successor version u + 1

• If version u + 1 does not exist (the version argument is the last version) then this version will not be deleted

• If there is one or more @renamedFrom(T, u + 1, anotherName) decorators, remove them.

• Change @renamedFrom(T, u, name) to @renamedFrom(T, u + 1, name)

  @renamedFrom(Versions.`2025-10-01-preview`, "oldName")
  @renamedFrom(Versions.`2025-11-01`, "oldName")
  newName: string;

@typeChangedFrom(T, u, type) decorator

• Based on the version referenced in the decorator, determine the immediate successor version u + 1

• If version u + 1 does not exist (the version argument is the last version) then this version will not be deleted

• If there is one or more @typeChangedFrom decorators referencing the immediate successor version, remove them.

• Change @typeChangedFrom(T, u, type) to @typeChangedFrom(T, u + 1, type)

  @typeChangedFrom(Versions.`2025-10-01-preview`, int32)
  @typeChangedFrom(Versions.`2025-11-01`, int32)
  newType: string;

@returnTypeChangedFrom(T, u, returnType) decorator

• Based on the version referenced in the decorator, determine the immediate successor version u + 1

• If version u + 1 does not exist (the version argument is the last version) then this version will not be deleted

• If there is one or more @returnTypeChangedFrom decorators referencing the immediate successor version, remove them.

• Change @returnTypeChangedFrom(T, u, returnType) to @returnTypeChangedFrom(T, u + 1, returnType)

  @returnTypeChangedFrom(Versions.`2025-10-01-preview`, void)
  @returnTypeChangedFrom(Versions.`2025-11-01`, void)
  move is ArmResourceActionSync<Widget, MoveRequest, MoveResponse>;

@madeOptional(T, u) decorator

• Based on the version referenced in the decorator, determine the immediate successor version u + 1

• If version u + 1 does not exist (the version argument is the last version) then this version will not be deleted

• If there is one or more @madeOptional decorators referencing the immediate successor version, remove them.

• Change @madeOption(T, u) to @madeOptional(T, u + 1)

  @madeOptional(Versions.`2025-10-01-preview`)
  @madeOptional(Versions.`2025-11-01`)
  nowOptional?: string;

@added(T, u) decorator

• Based on the version referenced in the decorator, determine the immediate successor version u + 1

• If version u + 1 does not exist (the version argument is the last version) then this version will not be deleted

• If there is one or more @added(T, u + 1) decorators referencing the immediate successor version

  • Remove them.

  • Change the version argument in the decorator to match the successor version [ @added(T, u) -> @added(T, u + 1)]

    @added(Versions.`2025-10-01-preview`)
    @added(Versions.`2025-11-01`)
    @added(Versions.`2025-11-01`)
    newType: string;

• If there is an @removed(T, u + 1) decorator referencing the immediate successor version

  • If the type does not occur in any previous version v < u, delete the type altogether

    @added(Versions.`2025-10-01-preview`)
    @removed(Versions.`2025-11-01`)
    goneType: string;

  • If the type does occur in a previous version, remove the @added(T, u) decorator.

    @added(Versions.`2025-06-01`)
    @added(Versions.`2025-10-01-preview`)
    @removed(Versions.`2025-11-01`)
    remainType: string;

• If there are no @added(T, u + 1) or @removed(T, u + 1) decorators referencing the immediate successor version, change the version in the decorator to the immediate successor version: [@added(T, u) -> @added(T, u + 1)]

  - @added(Versions.`2025-10-01-preview`)
  + @added(Versions.`2025-11-01`)
    @removed(Versions.`2026-02-01`)
    remainType: string;

@removed(T, u) decorator

• Based on the version referenced in the decorator, determine the immediate successor version u + 1

• If version u + 1 does not exist (the version argument is the last version) then this version will not be deleted

• If there is one or more @removed(T, u + 1) decorators referencing the immediate successor version

  • Remove them.

  • Change the version argument in the decorator to match the successor version [@removed(T, u) -> @removed(T, u + 1)]

    @removed(Versions.`2025-10-01-preview`)
    @removed(Versions.`2025-11-01`)
    @removed(Versions.`2025-11-01`)
    remainType: string;

• if there is one or more @added(T, u + 1) decorators in the immediate successor version

  • Remove the @removed(T, u) decorator

    @removed(Versions.`2025-10-01-preview`)
    @added(Versions.`2025-11-01`)
    remainType: string;

• If there are no @removed(T, u + 1) or @removed(T, u + 1) decorators referencing the immediate successor version, change the version in the decorator to the immediate successor version: [@removed(T, u) -> @removed(T, u + 1)]

  - @removed(Versions.`2025-10-01-preview`)
  + @removed(Versions.`2025-11-01`)
    remainType: string;

Removing the First version in the Specification

TypeSpec specs require no versioning decoration for the first version of a spec, and all versioning decorators except @removed have no impact on the type graph for subsequent versions and can be safely removed. Any @removed decorator referencing the first version should be treated as follows:

• If the decorated type does not occur in any subsequent versions, it can be removed
• If the decorated type does occur in subsequent versions, the version referenced in the @removed decorator should be updated to its immediate successor

Note that the last version of a specification should never be removed in a conversion, as if the last version is a preview, it will become the active preview.

Cleaning Up (optional)

After removing the preview versions, repeat the steps to normalize version decoration to remove redundant decoration.