Semantic Versioning (SemVer)

SemVer defines a strict sorting order for versions, which is critical for dependency resolution in tools like npm, pip, and Maven.

• Comparison Rules: Versions are compared from left to right (MAJOR, then MINOR, then PATCH). Numerical identifiers are compared numerically, and pre-release versions have lower precedence than normal versions (e.g., 1.0.0 > 1.0.0-beta > 1.0.0-alpha.1).
• Automation Enabler: This deterministic ordering allows package managers to automatically select compatible updates using caret (^) and tilde (~) ranges, trusting that a PATCH or MINOR increment will not break existing functionality.

The entire SemVer system hinges on a clearly defined Public API. This is the contract between your library/plugin and its consumers.

• What Constitutes the API: This includes exported functions, classes, configuration schemas, command-line interfaces, and the structure of data returned by your code.
• Documentation as Contract: Your API documentation (OpenAPI specs, JSDoc/TSDoc, README examples) forms part of this contract. Changes to documented behavior must trigger a MAJOR version bump.
• Private vs. Public: Changes to internal, undocumented code do not affect the public API and typically only warrant a PATCH version increment.

A formal specification that dictates the methods, data types, and behaviors that both a plugin host and its plugins must adhere to. It is the foundation upon which Semantic Versioning is applied.

• Defined via an Interface Definition Language (IDL) like Protocol Buffers or an OpenAPI Schema.
• Changes to this contract directly inform whether a version bump should be MAJOR, MINOR, or PATCH.
• A breaking change to the API contract, such as removing a method or changing a parameter type, necessitates a MAJOR version increase.

The design property of a system that ensures newer versions can still correctly interact with clients or plugins built for older versions. This is the core promise that Semantic Versioning helps communicate and manage.

• MAJOR version changes explicitly signal a break in backwards compatibility.
• MINOR version changes guarantee that existing functionality remains intact, preserving backwards compatibility while adding new features.
• Maintaining backwards compatibility is a primary constraint in plugin ecosystem design, directly influencing versioning strategy.

A directed graph that models the dependencies between plugins, used by the host system to determine the correct order for loading and initialization. Semantic Versioning constraints are applied to the edges of this graph.

• Each dependency edge specifies a version range (e.g., plugin-core >=1.2.0, <2.0.0).
• The host system or package manager uses these ranges to resolve a compatible set of plugin versions.
• A MAJOR version update of a core plugin may force updates across the entire dependency graph, a process managed through version constraints.

The defined sequence of states a plugin transitions through, including discovery, loading, initialization, execution, deactivation, and unloading. Semantic Versioning affects key lifecycle stages.

• During discovery, the host reads the plugin's version from its manifest.
• Loading may fail if version constraints (e.g., required host API version) are not satisfied.
• A MAJOR host version change may require plugins to implement new lifecycle interfaces or face deactivation.

A design pattern where a plugin's required dependencies (services, configurations) are provided ('injected') by the host framework. The stability of these injected service interfaces is governed by Semantic Versioning.

• The host's DI container provides services that are versioned entities themselves.
• A MINOR version increase of a provided service indicates new methods were added in a backwards-compatible way.
• A plugin declaring a dependency on a service must specify a compatible version range to ensure it receives an object with the expected API.

A system design principle where the failure or removal of a non-critical plugin causes a reduction in functionality rather than a complete system failure. Semantic Versioning aids in planning for this.

• If a required plugin updates to a new MAJOR version that breaks compatibility, the host can disable it and fall back to core functionality.
• Systems can be designed to tolerate a range of plugin versions (<next_major.0.0), allowing older plugins to remain active even as newer ones are added.
• This principle reduces the operational risk associated with version updates in a plugin ecosystem.