Re-display user's query with an error message if an error occurs

[simonw]

Refs #619

[simonw]

The one test failure here actually illustrates a larger problem: if the user specifies .json?_shape=array but an error occurs, what should we do?

Prior to this change we return the following JSON:

{
    "ok": false,
    "error": "You did not supply a value for binding 1.",
    "status": 500,
    "title": null
}

But this comes from the handle_500 higher level code here:

datasette/datasette/app.py

Lines 1251 to 1263 in eae3084

	info.update(
	{
	"ok": False,
	"error": message,
	"status": status,
	"title": title,
	}
	)
	headers = {}
	if self.ds.cors:
	headers["Access-Control-Allow-Origin"] = "*"
	if request.path.split("?")[0].endswith(".json"):
	await asgi_send_json(send, info, status=status, headers=headers)

[simonw]

This is the current test failure, but it actually another problem that we don't have tests in place for errors with different formats and shapes:

    def test_magic_parameters_cannot_be_used_in_arbitrary_queries(magic_parameters_client):
        response = magic_parameters_client.get(
            "/data.json?sql=select+:_header_host&_shape=array"
        )
        assert 400 == response.status
>       assert "You did not supply a value for binding 1." == response.json["error"]
E       TypeError: list indices must be integers or slices, not str

The test fails because response.json here is the empty list [].

[codecov]

Codecov Report

Merging #1346 (3bffc35) into main (7b106e1) will increase coverage by 0.14%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1346      +/-   ##
==========================================
+ Coverage   91.56%   91.71%   +0.14%     
==========================================
  Files          34       34              
  Lines        4282     4332      +50     
==========================================
+ Hits         3921     3973      +52     
+ Misses        361      359       -2     

Impacted Files	Coverage Δ
datasette/app.py	95.69% <ø> (-0.15%)	⬇️
datasette/renderer.py	94.20% <100.00%> (+0.17%)	⬆️
datasette/utils/__init__.py	94.36% <100.00%> (+0.05%)	⬆️
datasette/views/base.py	95.41% <100.00%> (+0.39%)	⬆️
datasette/views/database.py	97.28% <100.00%> (+0.09%)	⬆️
datasette/views/table.py	95.90% <100.00%> (+0.07%)	⬆️
datasette/tracer.py	85.05% <0.00%> (+3.44%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 7b106e1...3bffc35. Read the comment docs.