Describe map-of-slice values via additionalProperties#108
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cesartw
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Apr 23, 2026
| PrimSlices map[string][]string `json:"primSlices"` // Map of primitive slices. | ||
| StructSlice map[int64][]aStruct `json:"structSlice"` // Map of local struct slices. | ||
| OtherSlice map[string][]otherpkg.OtherStruct `json:"otherSlice"` // Map of cross-package struct slices. | ||
| } |
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the same happens for a map of maps but honestly I don't know if it should be addressed.
maps are too opened for web apis and feel lazy
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| } | |
| OtherMap map[string]map[string]otherpkg.OtherStruct `json:"otherMap"` // Other map comment. | |
| } |
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I've added nested map support there, although you'd be best positioned to know how it might impact performance .
cesartw
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Apr 23, 2026
rafaeljusto
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Apr 23, 2026
The `*ast.MapType` handler only resolved map values of kind `*ast.Ident`/`*ast.SelectorExpr`, so fields typed as `map[K][]T` silently dropped the element type and rendered as `type: object` with no `additionalProperties`. Consumers (openapi-typescript, etc.) then saw an opaque `Record<string, never>` where the server actually emits a map of arrays. Detect a slice value up front and build an array schema for it via `resolveArray`, attaching it as `additionalProperties`. While here, make `prefixPropertyReferences` recurse into nested `additionalProperties` and `items` so references inside the new array schema get the `#/definitions/...` prefix they need. Fixture `struct-map` grows three new cases covering primitive, local, and cross-package slice element types.
Keeps fieldToSchema's cyclomatic complexity under the gocyclo threshold (65). Pure refactor — no behavior change, no new tests needed.
A `map[K]map[K2]V` field previously dropped the inner map's value type: `findTypeIdent` only handles `Ident`/`SelectorExpr`, so a map-typed value fell through to the open-object fallback. Detect `*ast.MapType` up front and recurse, producing nested `additionalProperties`. `prefixSchemaReferences` already walks `AdditionalProperties`, so `$ref`s inside the nested schema are rewritten correctly without further changes.
`resolveMap` compared the raw Go type name against the JSON-schema primitive set, so `int`/`bool`/`float64` failed the check and fell through to an open-object fallback. Run `JSONSchemaType` first so `int`→`integer`, `bool`→`boolean`, etc. match.
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What this does
Fixes a gap in
*ast.MapTypehandling. Fields typed asmap[K][]Tpreviously dropped the element type — they rendered astype: objectwith noadditionalProperties, which downstream tools (openapi-typescript, etc.) flatten toRecord<string, never>.The value-type resolver (
findTypeIdent) only handlesIdent/SelectorExpr, so a slice value fell through the error branch. This PR detects*ast.ArrayTypevalues up front and builds an array schema via the existingresolveArray, then attaches it asadditionalProperties.While here,
prefixPropertyReferencesnow recurses into nesteditemsandadditionalProperties, so$refvalues inside the new array schema get the#/definitions/...prefix.Before / after
Given
map[int64][]SomeStruct:Before
After
Tests
Extended the existing
struct-mapfixture with three new fields covering primitive, local-struct, and cross-package-struct slice element types. All existing tests still pass.Why
map[K][]Tis a natural Go shape for "group these items by X" response payloads. Without this fix, any such field ends up as an opaque object in the spec and consumers lose all type information about the slice elements. Fixing it here avoids per-field workarounds in downstream type generators.