[REQ][Rust] Add additionalProperties to the generated code

[Vardaleb]

Is your feature request related to a problem? Please describe.

Some openAPI specs do not contain every property they actually return. Right now it is not possible to access those properties

Describe the solution you'd like

The solution would be to include all undefined properties in the generated code, by modifying the model.mustache file like this:

--- /proc/self/fd/14	2025-03-25 10:57:36.081920827 +0100
+++ templates/model.mustache	2025-03-25 09:53:47.536340813 +0100
@@ -148,6 +148,8 @@
     ### Option End (and trailing comma)
     }}{{#isNullable}}>{{/isNullable}}{{^required}}>{{/required}},
 {{/vars}}
+    #[serde(flatten)]
+    pub additional_properties: std::collections::HashMap<String, serde_json::Value>,
 }
 
 impl {{{classname}}} {
@@ -169,6 +171,7 @@
             {{#vars}}
             {{{name}}}{{^required}}: None{{/required}}{{#required}}{{#isModel}}{{^avoidBoxedModels}}: {{^isNullable}}Box::new({{{name}}}){{/isNullable}}{{#isNullable}}if let Some(x) = {{{name}}} {Some(Box::new(x))} else {None}{{/isNullable}}{{/avoidBoxedModels}}{{/isModel}}{{/required}},
             {{/vars}}
+            additional_properties: std::collections::HashMap::new(),
         }
     }
 }

[Vardaleb]

For now, I have copied the original file and modified it in my project. But this is not very sustainable, when the original file changes in he future

[JMLX42]

@Vardaleb would you mind opening a PR for this?

[NoxTav]

@Vardaleb About your PR, I've been working on the same issue on my side, and your fix adds the field to all the models, whereas we should know from the openapi.json file which have additionalProperties set.

I encountered 2 types of additionalProperties, so here is my proposed fix:

{{!### in the struct}}
{{#composedSchemas.allOf}}
{{#additionalProperties}}
    #[serde(flatten)]
    pub additional_properties: std::collections::HashMap<String, serde_json::Value>,
{{/additionalProperties}}
{{/composedSchemas.allOf}}
{{^composedSchemas.allOf}}
{{#isAdditionalPropertiesTrue}}
    #[serde(flatten)]
    pub additional_properties: std::collections::HashMap<String, serde_json::Value>,
{{/isAdditionalPropertiesTrue}}
{{/composedSchemas.allOf}}

{{!### in new()}}
{{!### allOf is an array}}
{{#composedSchemas.allOf}}
{{#additionalProperties}}
           additional_properties: std::collections::HashMap::new(),
{{/additionalProperties}}
{{/composedSchemas.allOf}}
{{^composedSchemas.allOf}}
{{#isAdditionalPropertiesTrue}}
           additional_properties: std::collections::HashMap::new(),
{{/isAdditionalPropertiesTrue}}
{{/composedSchemas.allOf}}

In my test case, I have a map of String to String and a map of String to JSON.

Maybe in the second case, we could use additionalPropertyType to set the type dynamically, but I didn't test it and wouldn't know how to set the value by default.

And there might be other ways to set additionalProperties, I haven't encountered.