Module diff 

Schema diff (spec 0002 §9, §12).

A pure function producing a stable SchemaDiff between two InMemorySchema values. The output is designed to be serialised as JSON for CI “schema-compat” gates: consumer projects run cypher schema diff old.toml new.toml and compare the breaking list to decide whether the new schema is a drop-in replacement.

What counts as “breaking”

At v0 the following changes are classed as breaking:

• A label is removed (existing queries that reference the label break).
• A property on an existing label loses required = true, changes type, or is removed entirely.
• A relationship type is removed.
• A rel type’s start_labels or end_labels shrink (existing patterns may now be rejected by the semantic pass).
• A rel type changes or loses a property (same rules as labels).
• A parameter is removed, or changes type, or loses its default value.

Non-breaking changes land in adds:

• New labels, rel types, parameters.
• New optional properties on an existing declaration.
• A rel type’s endpoint lists expanding (more labels allowed).
• A parameter gaining a default.

The diff is structural: it does not know about the semantic content of queries that depend on the schema. A downstream CI gate that wants stronger compatibility should check breakages against its own corpus.

Structs

DiffEntry

One discrete change recorded in a SchemaDiff.

SchemaDiff

Structured diff between two schemas.

Functions

diff

Compute the diff between old and new.