Module: McpDiff::Core::SchemaDiff

Defined in:
lib/mcp_diff/core/schema_diff.rb

Overview

Pragmatic structural diff of a JSON-Schema object schema (D9). Recognizes type / enum / required / properties / description / default; anything it cannot prove compatible surfaces as an *-opaque change so the incompatible catch-all rules fire loudly instead of silently passing. Port of core/src/schema-diff.ts. SchemaChange hashes use symbol keys (internal).

Constant Summary collapse

PARAM_HANDLED = 
%w[type enum description default title].freeze
TOP_HANDLED = 
%w[properties required description title $schema].freeze

Class Method Summary collapse

Class Method Details

.as_obj(value) ⇒ Object 



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# File 'lib/mcp_diff/core/schema_diff.rb', line 20

def as_obj(value)
  value.is_a?(Hash) ? value : nil
end

.diff_object_schema(before_raw, after_raw) ⇒ Object 



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# File 'lib/mcp_diff/core/schema_diff.rb', line 108

def diff_object_schema(before_raw, after_raw)
  return [] if Canonical.deep_equal(before_raw, after_raw)

  before = as_obj(before_raw)
  after = as_obj(after_raw)
  return [{ kind: "schema-changed-opaque" }] unless before && after

  changes = []
  b_props = as_obj(before["properties"]) || {}
  a_props = as_obj(after["properties"]) || {}
  b_req = required_set(before)
  a_req = required_set(after)

  b_props.keys.sort.each { |p| changes << { kind: "param-removed", param: p } unless a_props.key?(p) }
  a_props.keys.sort.each do |p|
    changes << { kind: "param-added", param: p, required: a_req.include?(p) } unless b_props.key?(p)
  end
  a_req.to_a.sort.each do |p|
    changes << { kind: "required-added", param: p, existed_before: b_props.key?(p) } unless b_req.include?(p)
  end
  b_req.to_a.sort.each do |p|
    changes << { kind: "required-removed", param: p } if !a_req.include?(p) && a_props.key?(p)
  end
  b_props.keys.sort.each { |p| diff_param(p, b_props[p], a_props[p], changes) if a_props.key?(p) }

  unless Canonical.deep_equal(strip_keys(before, TOP_HANDLED), strip_keys(after, TOP_HANDLED))
    changes << { kind: "schema-changed-opaque" }
  end

  changes
end

.diff_param(param, before_raw, after_raw, changes) ⇒ Object 



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# File 'lib/mcp_diff/core/schema_diff.rb', line 55

def diff_param(param, before_raw, after_raw, changes)
  return if Canonical.deep_equal(before_raw, after_raw)

  before = as_obj(before_raw)
  after = as_obj(after_raw)
  unless before && after
    changes << { kind: "param-changed-opaque", param: param }
    return
  end

  diff_param_type(param, before, after, changes)
  diff_param_enum(param, before, after, changes)

  changes << { kind: "description-changed", param: param } if before["description"] != after["description"]
  changes << { kind: "default-changed", param: param } unless Canonical.deep_equal(before["default"], after["default"])

  unless Canonical.deep_equal(strip_keys(before, PARAM_HANDLED), strip_keys(after, PARAM_HANDLED))
    changes << { kind: "param-changed-opaque", param: param }
  end
end

.diff_param_enum(param, before, after, changes) ⇒ Object 



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# File 'lib/mcp_diff/core/schema_diff.rb', line 93

def diff_param_enum(param, before, after, changes)
  b_e = enum_values(before)
  a_e = enum_values(after)
  if !b_e.nil? && !a_e.nil?
    removed = b_e.reject { |v| a_e.any? { |w| Canonical.deep_equal(v, w) } }
    added = a_e.reject { |v| b_e.any? { |w| Canonical.deep_equal(v, w) } }
    changes << { kind: "enum-value-removed", param: param, values: removed } unless removed.empty?
    changes << { kind: "enum-value-added", param: param, values: added } unless added.empty?
  elsif !b_e.nil? && a_e.nil?
    changes << { kind: "enum-constraint-removed", param: param }
  elsif b_e.nil? && !a_e.nil?
    changes << { kind: "enum-constraint-added", param: param }
  end
end

.diff_param_type(param, before, after, changes) ⇒ Object 



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# File 'lib/mcp_diff/core/schema_diff.rb', line 76

def diff_param_type(param, before, after, changes)
  b_t = type_set(before)
  a_t = type_set(after)
  types_equal = (b_t.nil? && a_t.nil?) ||
                (!b_t.nil? && !a_t.nil? && subset?(b_t, a_t) && subset?(a_t, b_t))
  return if types_equal

  label = { before: type_label(b_t), after: type_label(a_t) }
  if b_t.nil? || (!a_t.nil? && subset?(a_t, b_t))
    changes << { kind: "type-narrowed", param: param }.merge(label)
  elsif a_t.nil? || subset?(b_t, a_t)
    changes << { kind: "type-widened", param: param }.merge(label)
  else
    changes << { kind: "param-changed-opaque", param: param }
  end
end

.enum_values(schema) ⇒ Object 



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# File 'lib/mcp_diff/core/schema_diff.rb', line 46

def enum_values(schema)
  e = schema["enum"]
  e.is_a?(Array) ? e : nil
end

.format_values(values) ⇒ Object 



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# File 'lib/mcp_diff/core/schema_diff.rb', line 140

def format_values(values)
  values.map(&:to_json).join(", ")
end

.required_set(schema) ⇒ Object 



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# File 'lib/mcp_diff/core/schema_diff.rb', line 24

def required_set(schema)
  req = schema["required"]
  Set.new(req.is_a?(Array) ? req.select { |r| r.is_a?(String) } : [])
end

.strip_keys(obj, keys) ⇒ Object 



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# File 'lib/mcp_diff/core/schema_diff.rb', line 51

def strip_keys(obj, keys)
  obj.reject { |k, _| keys.include?(k) }
end

.subset?(a, b) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/mcp_diff/core/schema_diff.rb', line 42

def subset?(a, b)
  a.all? { |x| b.include?(x) }
end

.type_label(set) ⇒ Object 



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# File 'lib/mcp_diff/core/schema_diff.rb', line 38

def type_label(set)
  set.nil? ? "(any)" : set.to_a.sort.join("|")
end

.type_set(schema) ⇒ Object

type as a set of names; nil = unspecified (accepts anything).



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# File 'lib/mcp_diff/core/schema_diff.rb', line 30

def type_set(schema)
  t = schema["type"]
  return Set[t] if t.is_a?(String)
  return Set.new(t.select { |x| x.is_a?(String) }) if t.is_a?(Array)

  nil
end