PDE/API Tools/Use Cases

Introduction

API Tools has been designed to aid developers maintaining good APIs, version numbers, mitigating internal usage across bundles and eliminating internal code leaks to API. The following are the original use cases discussed while designing the tooling.

Binary Compatibility Reporting (Batch Mode)

Two versions of the same API profile are compared for binary compatibility. An XML file is produced summarizing any incompatibilities. The comparison tool can be invoked from the command line as a stand alone Java application specifying the profiles to compare and which parts of the profiles to consider (for example, only compare portions of the profile that are deemed to be API).

The report includes errors regarding component version identifiers that have not been incremented properly. As well, if source code is available for the "newer" API profile, the report includes missing @since Javadoc tags.

An exclude list should be added to filter out the cases where the binary incompatibility is "under control", i.e. approved by the PMC. The best way to maintain the exclude list would be to have a Javadoc tag in the source code that mentions why this is a breakage. Something like:

@breakage-addition ...... 
@breakage-remove Type#member .....

The removals would be located on the parent of the removed member.

Updating the source code improves the traceability of a breakage and allows readers of the source code to get a better picture without the need to check another document.

Binary Compatibility Reporting (IDE Mode)

Workspace projects are compared to a baseline API profile for binary compatibility. Incompatibilities are flagged in source files using markers (that also appear in the Problems view). The user configures the severity of errors produced. A set of external API profiles are managed in the workspace and one is specified as the baseline against which workspace projects are compared. The user defines the workspace API profile as combination of workspace projects and external API components.

Compatibility errors are updated incrementally or in full depending on the build setting in the workspace (i.e. auto-build vs. manual/full build). Error markers are also produced for components with incorrect version numbers and missing @since Javadoc tags. Quick fixes are available to address the problems.

An exclude list should be added to filter out the cases where the binary incompatibility is "under control", i.e. approved by the PMC. The best way to maintain the exclude list would be to have a Javadoc tag in the source code that mentions why this is a breakage. Something like:

@breakage-addition ...... 
@breakage-remove Type#member .....

The removals would be located on the parent of the removed member.

Updating the source code improves the traceability of a breakage and allows readers of the source code to get a better picture without the need to check another document.

API Usage Reporting (Batch Mode)

The most common API usage report locates illegal use of APIs among components in a single API profile - i.e. access to non-API types, methods, and fields; and illegal extension, implementing, or instantiating. The API usage scanner can be invoked as a stand alone Java application to examine all or specific portions of an API profile for illegal API use. An XML file is produced as output.

The API scanner should also support scanning for use of a specific component. For example, rather than scanning component X to determine what use it makes of other APIs, scan a profile to find all uses of the API in X.

Another interesting scan would be to report what parts of a profile or component would be broken when migrating to another version of a required component. For example, the internals of a component often change or can be removed in a newer release of the component.

API Usage Reporting (IDE Mode)

The Eclipse SDK already provides compiler warnings for discouraged accesses between bundles - which is the same as referencing non-API code. Rather than duplicate this effort, the integrated tooling could just report illegal implementing, sub-classing, and instantiation. Problem markers would be created incrementally, similar to the support for binary compatibility.

API Usage Searching (IDE Mode)

Similar to the extensive search facility provided by JDT for searching projects in the workspace, API tooling could support searching of API profiles. This would allow to search for all uses of a component, type, method, etc., from an API profile or component.

Version Management

In addition to reporting missing @since tags and incorrect bundle version numbers (based on the Eclipse bundle versioning scheme), the tooling will provide quick fixes to correct these problems.

As well, the tooling will assist developers on determining compatible version ranges of required bundles (plug-ins). Developers often increment the lower bound of version ranges of required bundles in each major release. Usually this makes sense (for example, the debug platform's UI bundle usually requires the latest debug core bundle). However, sometimes this is unnecessary, and a bundle may run perfectly fine with an older version of a required bundle. Given a range of versions of a required bundle, API tooling will be able to determine which versions of the bundle satisfy API (and non-API) accesses.

Building API Components & Baselines

Provide a mechanism to export API components. This could be used in a build process or from the IDE.

Javadoc Tags, API Visibilities & Restrictions

The platform provides a default set of Javadoc tags. The tags and the Java members they apply to are:

1. @noreference - Indicates that other bundles must not reference this member by name. I.e., the member is internal. This tag is intended to be used very rarely when a public class wants to restrict access to one of its members, but is not intended for general usage. This tag is ignored on all other members except for method declarations and non-final field declarations.
2. @noimplement - Indicates that other bundles must not implement this interface. This tag is ignored for all types except for interfaces.
3. @noextend - Indicates that other bundles must not extend the class or interface it appears on. This tag is ignored for all members that are not interfaces or classes.
4. @noinstantiate - Indicates that other bundles must not create instances of this class. This tag is ignored for all other types that are not classes.
5. @nooverride - Indicates that other bundles must not extend (re-implement with a call to the overridden parent) or re-implement (with no call to the overridden parent) this method. This tag is ignored for all other members except method declarations.