Assembly comparison for jsii
npm install jsii-diff__jsii-diff__ compares two jsii assemblies for compatibility.
In the future, it will be able to do generic comparisons.
But for
now it will compare assemblies for API compatibility, and exit
with a non-zero exit code if any __stable__ or __deprecated__ APIs have had incompatible changes.
API items that have no stability are treated as __stable__.
To treat unmarked API items as experimental, pass the --default-experimental flag.
To compare two JSII packages:
``console`
jsii-diff
Packages can be identified by either:
* __A path__, in which case it should be the path to a JSII package directory,
or to a .jsii file.npm:[
* __An NPM package specifier__ of the form , in@version
which case the indicated version is downloaded and used. If ispackage
left out, the latest version will be used. If is left out,.jsii
the assembly name of in the current directory will be used.
To compare current package against latest published NPM release:
`console`
jsii-diff npm:
By default only incompatible changes to stable or deprecated APIs are treated as errors and will fail the command.experimental
Changes to or external APIs emit a warning.
Change this behavior with the --error-on flag:
`console`
jsii-diff npm:
The following --error-on groups are available:
| --error-on | Stabilities that cause an ERROR |prod
| ------------------ | -------------------------------------------------- |
| (default) | stable, deprecated |non-experimental
| | stable, deprecated, external |all
| | stable, deprecated, experimental, external |
__jsii-diff__ will assert that code written against version __A__ of a library
will still typecheck when compiled against version __B__ of that library. It
does this by verifying the following properties:
* Any type (class/interface/enum) in __A__ must also exist in __B__.
* Enums have only added members.
* Classes and interfaces have only added members, or modified existing
members in an allowed way.
* Property types are the same or have been strengthened (see below).
* Methods have only added optional arguments, existing argument types have
only been weakened, and the return type has only been strengthened (see below).
Strengthening a type refers to excluding* more possible values. Changing
a field from optional to required, or changing a type from any tostring
are examples of strengthening.
As the opposite of strengthening, weakening refers to allowing* more
possible values. Changing a field from required to optional, or
changing a type to a superclass or interface are examples of weakening.
An API can change in the following way without breaking its consumer:
It can weaken its input (require less* from the caller); and
It can strengthen its output (guarantee more* to the caller).
Structs (interfaces consisting completely of readonly properties) are
treated as bags of data. Their API compatibility will be evaluated depending
on whether they appear in input or output position of operations.
Structs are weakened* if all types of all of its properties are weakened.
Normally removing properties would also be considered weakening, but
because that may cause references to the fields in existing code bases to
become undefined (which is not allowed in most programming languages) we
disallow removing properties.
Structs are strengthened* if all types of all of its properties are
strengthened, or if fields are added.
__jsii-diff__ will check the evolution of structs against their position
in an operation, similar to other types. Input structs may be weakened,
and output structs may be strengthened.
Classes and non-struct interface types are considered "reference types". By
default we treat them as being the result of a function call:
* Class instances are the return values calling their constructors.
* Interfaces are only ever implemented by objects returned from the framework,
or returned by factory functions.
This means their evolution falls under the rules of "strengthening": they
may only add fields, never take any away or make them optional.
#### @subclassable
Some classes or interfaces may be intended to be implemented by consumers.
Those should be marked with the docstring tag @subclassable.
This will effectively cause changes against those types to be checked against
the rules for weakening as well (i.e., no new (abstract) fields or members
added). This is necessary because otherwise any existing implementor of that
interface would be broken, since they wouldn't be implementing the new
abstract members yet.
@subclassable is not the default since most interfaces are not intended
for subclassing, but treating them as such would limit the evolvability of
libraries too much.
Sometimes you want to move forward with a change, even if it would technically
be a breaking change to your API. In order to do that, run jsii-diff
with the flag . It will then print an identifier for every violation
between square brackets, for example:
`
$ jsii-diff
IFACE pkg.MyStruct: formerly required property 'prop' is optional: returned from pkg.IConsumer.someMethod [weakened:pkg.MyStruct]
To accept a breaking finding, put the key (in this example weakened:pkg.MyStruct)allowed-breaking-changes.txt
into a text file, for example , and pass it tojsii-diff as an ignore file:
`
$ jsii-diff
(no error)
If you've moved API elements around between versions of your library, you can
put a special ignore marker starting with move: into your --ignore-file. To:
separate the old and new class names, you can use , , or whitespace.
For example:
`
move:package.OldClassName package.NewClassName
move:package.OldClassName:package.NewClassName
move:package.OldClassName, package.NewClassName
Moving API elements is always breaking, but using this feature you can confirm
that you at least didn't break anything in the API surface of the moved classes
themselves.
See BREAKING_CHANGES.md for more information.
__jsii-diff__ is distributed under the
Apache License, Version 2.0.