Custom pages mechanism, refs #648

[simonw]

Refs #648. TODO:

• Pass a view_name to render_template()
• Mechanism for custom status code / headers / redirect
• Documentation

[simonw]

Stretch goal: it would be neat if these pages could return custom HTTP headers (eg content-type) and maybe even status codes (eg for redirects) somehow.

I think I could do that with a custom template function - if that function is called during the render then we follow those instructions instead of returning the rendered HTML.
#648 (comment)

[simonw]

Design challenge: the function that can be called in the custom template to return a custom status code and/or headers.

Proposed design:

{{ custom_headers({"x-foo": "bar"}) }}
{{ custom_status_code(404) }}

Or should I combine them into one function?

{{ custom_headers({"x-foo": "bar"}, status=404) }}

A common use-case here would be a redirect. How should that look?

{{ custom_redirect("/foo") }} - defaults to 301
{{ custom_redirect("/foo", status=302) }}

Maybe avoid dictionary syntax entirely:

{{ custom_header("x-foo", "bar") }}

[simonw]

I'm going with custom_header(name, value), custom_status(numeric_code), custom_redirect("URL").

[simonw]

Just needs documentation now.