Re: [PATCH v1 3/9] qapi: golang: Generate qapi's struct types in Go

[Daniel P . Berrangé]

On Wed, Sep 27, 2023 at 01:25:38PM +0200, Victor Toso wrote:
> This patch handles QAPI struct types and generates the equivalent
> types in Go. The following patch adds extra logic when a member of the
> struct has a Type that can take JSON Null value (e.g: StrOrNull in
> QEMU)
> 
> The highlights of this implementation are:
> 
> 1. Generating an Go struct that requires a @base type, the @base type
>    fields are copied over to the Go struct. The advantage of this
>    approach is to not have embed structs in any of the QAPI types.
>    Note that embedding a @base type is recursive, that is, if the
>    @base type has a @base, all of those fields will be copied over.
> 
> 2. About the Go struct's fields:
> 
>    i) They can be either by Value or Reference.
> 
>   ii) Every field that is marked as optional in the QAPI specification
>       are translated to Reference fields in its Go structure. This
>       design decision is the most straightforward way to check if a
>       given field was set or not. Exception only for types that can
>       take JSON Null value.
> 
>  iii) Mandatory fields are always by Value with the exception of QAPI
>       arrays, which are handled by Reference (to a block of memory) by
>       Go.
> 
>   iv) All the fields are named with Uppercase due Golang's export
>       convention.
> 
>    v) In order to avoid any kind of issues when encoding or decoding,
>       to or from JSON, we mark all fields with its @name and, when it is
>       optional, member, with @omitempty
> 
> Example:
> 
> qapi:
>  | { 'struct': 'BlockdevCreateOptionsFile',
>  |   'data': { 'filename': 'str',
>  |             'size': 'size',
>  |             '*preallocation': 'PreallocMode',
>  |             '*nocow': 'bool',
>  |             '*extent-size-hint': 'size'} }
> 
> go:
> | type BlockdevCreateOptionsFile struct {
> |     Filename       string        `json:"filename"`
> |     Size           uint64        `json:"size"`
> |     Preallocation  *PreallocMode `json:"preallocation,omitempty"`
> |     Nocow          *bool         `json:"nocow,omitempty"`
> |     ExtentSizeHint *uint64       `json:"extent-size-hint,omitempty"`
> | }

Note, 'omitempty' shouldn't be used on pointer fields, only scalar
fields. The pointer fields are always omitted when nil.


With regards,
Daniel
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