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Macro recursion issue: Variables in macros are not stored on the stack #577

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oberlies opened this issue Nov 6, 2015 · 2 comments · Fixed by #653
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Macro recursion issue: Variables in macros are not stored on the stack #577

oberlies opened this issue Nov 6, 2015 · 2 comments · Fixed by #653
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@oberlies
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oberlies commented Nov 6, 2015

Consider the following template that renders a list of fully qualified property names from a JSON schema:

{% macro typeTable(node, prefix = "", name = "" %}
  {% set nodeName = prefix + ("." if prefix) + name) %}
  {% if nodeName %}
    <tr>
      <td><code>{{ nodeName | safe }}</code></td>
      <td>{{ node.type }}</td>
      <td>
        {% markdown %}{{ node.description }}{% endmarkdown %}
      </td>
    </tr>
  {% endif %}
  {% if node.type == "object" %}
    {% for propName, propSpec in node.properties %}
      {{ typeTable(propSpec, nodeName, propName) }}
    {% endfor %}
  {% endif %}
{% endmacro %}

<body>
  <table class='table table-bordered'>
    <thead>
      <tr>
        <th>Qualified name</th>
        <th>Type</th>
        <th>Description</th>
      </tr>
    </thead>
    <tbody>
      {{ typeTable(schema) }}
    </tbody>
  </table>
</body>

Where schema is for example the following JSON schema

{
  "$schema": "http://json-schema.org/draft-04/schema",
  "type": "object",
  "properties": {
    "id": {
      "type": "string",
      "description": "The ID of the node"
    },
    "name": {
      "type": "string",
      "description": "The name of the node"
    },
    "status": {
      "type": "object",
      "description": "The status of the node",
      "properties": {
        "vm": {
          "type": "string"
        },
        "app": {
          "type": "string"
        }
      }
    },
    "url": {
      "type": "string",
      "format": "uri",
      "description": "The URL of the node"
    }
  }
}

The expected result is a table with the following "qualified names":

id
name
status
status.vm
status.app
url

However the variable nodeName seems to scoped per declaration (i.e. there is only one instance) and not scoped per invocation. This means that changes to nodeName in recursive calls of typeTable can be seen by the caller. This results in the following "qualified names":

id
id.name
id.name.status
id.name.status.vm
id.name.status.vm.app
id.name.status.vm.app.url
@oberlies
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oberlies commented Nov 6, 2015

The workaround for this issue is to not use any variables in macros that are called recursively. Instead, declare all local variables as parameters with default values. I.e. instead of

{% macro typeTable(node, prefix = "", name = "" %}
  {% set nodeName = prefix + ("." if prefix) + name) %}
  ...

write

{% macro typeTable(node, prefix = "", name = "", nodeName = prefix + ("." if prefix) + name) %}
  ...

Nevertheless, it would be nice if variables in macros worked as expected

@carljm carljm added the bug label Nov 6, 2015
@ptusch
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ptusch commented Jan 19, 2016

Vote up
A really annoying bug.

@oyyd oyyd mentioned this issue Jan 28, 2016
Merged
@carljm carljm mentioned this issue Feb 4, 2016
Merged
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Do not resolve up when setting a variable in macro. oyyd/nunjucks
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@carljm @oberlies @ptusch