"Templates considered" comment broken in >=0.35

[chrishas35]

Noticed that the "Templates Considered" comment is missing in 0.37. Believe I traced it back to #664 as you can see it in https://v0-34.datasette.io/ but not https://v0-35.datasette.io/. Looking at the template context debug between the two you can see what is missing from 0.35 vs. 0.34:

<     "datasette_version": "0.34",
<     "app_css_hash": "ffa51a",
<     "select_templates": [
<         "*index.html"
<     ],
<     "zip": "<class 'zip'>",
<     "body_scripts": [],
<     "extra_css_urls": "<generator object BaseView._asset_urls at 0x7f6529ac05f0>",
<     "extra_js_urls": "<generator object BaseView._asset_urls at 0x7f6529ac0660>",
<     "format_bytes": "<function format_bytes at 0x7f652a1588b0>",
<     "database_url": "<bound method BaseView.database_url of <datasette.views.index.IndexView object at 0x7f6529b03e50>>",
<     "database_color": "<bound method BaseView.database_color of <datasette.views.index.IndexView object at 0x7f6529b03e50>>"
---
>     "datasette_version": "0.35",
>     "database_url": "<bound method BaseView.database_url of <datasette.views.index.IndexView object at 0x7f6140dacd90>>",
>     "database_color": "<bound method BaseView.database_color of <datasette.views.index.IndexView object at 0x7f6140dacd90>>"

[simonw]

I'm going to debug this using git bisect run - the same technique I used in #716 - #716 (comment)

[simonw]

Just need the one checking script to run with bisect this time:

check_templates_considered.py

import asyncio
import pathlib
from datasette.app import Datasette
import httpx


async def run_check():
    ds = Datasette([])
    async with httpx.AsyncClient(app=ds.app()) as client:
        response = await client.get("http://localhost/")
        assert 200 == response.status_code
        assert "Templates considered" in response.text


if __name__ == "__main__":
    loop = asyncio.get_event_loop()
    loop.run_until_complete(run_check())

[simonw]

git bisect start master 0.34
git bisect run python check_templates_considered.py

[simonw]

$ git bisect start master 0.34
Bisecting: 32 revisions left to test after this (roughly 5 steps)
[dc80e779a2e708b2685fc641df99e6aae9ad6f97] Handle scope path if it is a string
$ git bisect run python check_templates_considered.py
running python check_templates_considered.py
Traceback (most recent call last):
...
AssertionError
Bisecting: 15 revisions left to test after this (roughly 4 steps)
[7c6a9c35299f251f9abfb03fd8e85143e4361709] Better tests for prepare_connection() plugin hook, refs #678
running python check_templates_considered.py
Traceback (most recent call last):
...
AssertionError
Bisecting: 7 revisions left to test after this (roughly 3 steps)
[0091dfe3e5a3db94af8881038d3f1b8312bb857d] More reliable tie-break ordering for facet results
running python check_templates_considered.py
Traceback (most recent call last):
...
AssertionError
Bisecting: 3 revisions left to test after this (roughly 2 steps)
[ce12244037b60ba0202c814871218c1dab38d729] Release notes for 0.35
running python check_templates_considered.py
Traceback (most recent call last):
...
AssertionError
Bisecting: 1 revision left to test after this (roughly 1 step)
[70b915fb4bc214f9d064179f87671f8a378aa127] Datasette.render_template() method, closes #577
running python check_templates_considered.py
Traceback (most recent call last):
...
AssertionError
Bisecting: 0 revisions left to test after this (roughly 0 steps)
[286ed286b68793532c2a38436a08343b45cfbc91] geojson-to-sqlite
running python check_templates_considered.py
70b915fb4bc214f9d064179f87671f8a378aa127 is the first bad commit
commit 70b915fb4bc214f9d064179f87671f8a378aa127
Author: Simon Willison <swillison@gmail.com>
Date:   Tue Feb 4 12:26:17 2020 -0800

    Datasette.render_template() method, closes #577
    
    Pull request #664.

:040000 040000 def9e31252e056845609de36c66d4320dd0c47f8 da19b7f8c26d50a4c05e5a7f05220b968429725c M	datasette
bisect run success

It was 70b915f - the same bad commit that caused #716!

[simonw]

Here's why: the BaseView.render() method is running jinja_env.select_template() now here:

datasette/datasette/views/base.py

Lines 75 to 88 in e89b0ef

	async def render(self, templates, request, context):
	template = self.ds.jinja_env.select_template(templates)
	template_context = {
	**context,
	**{
	"database_url": self.database_url,
	"database_color": self.database_color,
	},
	}
	return Response.html(
	await self.ds.render_template(
	template, template_context, request=request, view_name=self.name
	)
	)

Which means this logic is always called with a template, not a list of strings:

datasette/datasette/app.py

Lines 555 to 571 in e89b0ef

	async def render_template(
	self, templates, context=None, request=None, view_name=None
	):
	context = context or {}
	if isinstance(templates, Template):
	template = templates
	select_templates = []
	else:
	if isinstance(templates, str):
	templates = [templates]
	template = self.jinja_env.select_template(templates)
	select_templates = [
	"{}{}".format(
	"*" if template_name == template.name else "", template_name
	)
	for template_name in templates
	]

[simonw]

So I think the fix is to move the "select_templates": select_templates context setting bit to here instead:

datasette/datasette/views/base.py

Lines 75 to 83 in e89b0ef

	async def render(self, templates, request, context):
	template = self.ds.jinja_env.select_template(templates)
	template_context = {
	**context,
	**{
	"database_url": self.database_url,
	"database_color": self.database_color,
	},
	}