[WIP] Document policy for adding custom test jobs/components to rust-lang/rust CI

[jieyouxu]

Caution

Do not merge, this is open for feedback, blocked on the MCP being seconded and accepted.

Tip

For review purposes, this PR will initially have a lot of intermediate commits to make review history more clear, but they are intended be squashed away before ready for merge.

MCP: rust-lang/compiler-team#845
MCP thread: #t-compiler/major changes > Policy: Require MCP and relevant team nom… compiler-team#845
rust-lang/rust issue: rust-lang/rust#137960

Following discussions in https://rust-lang.zulipchat.com/#narrow/channel/131828-t-compiler/topic/RFL.20CI.20Job.

Not sure if T-infra wants this to be documented somewhere... cc @rust-lang/infra

r? @davidtwco (or @wesleywiser)

Rendered

[jieyouxu]

Blocked on opening an MCP for this first.
@rustbot blocked

EDIT: rust-lang/compiler-team#845

[Kobzol]

Looks great, thanks. The diagram kind of shows how desynchronized are the decision processes between t-compiler and t-libs (and other teams) currently :) Left some comments.

[davidtwco]

Some nits, but this looks great.

[jieyouxu]

Changes since last review:

• Hard-wrapped to 100 columns.
• Changed terminology to use "ecosystem/integration test jobs/components" instead.
• Spelled out the process (instead of just having the diagram).
• Adjusted process (text and diagram) to ask infra about capacity first (discussed in #t-infra > Policy for adding custom test jobs/components to r-l/r CI).
• Dropped mentions about ping groups because only team members + certain WG members can use triagebot ping group anyway.
• Adjusted scope wording.

[jieyouxu]

FIXME(jieyouxu): rename this file to sth like ecosystem-integration-tests.md and fix links before merge.

[jieyouxu]

Changes since last push:

• I significantly reformatted the policy template to make it much more edit-friendly, as I see in Enable autodiff testcases in CI compiler-team#855 that it was hard to work with.

[jieyouxu]

Changes since last push (take 2):

• Looking at Enable autodiff testcases in CI compiler-team#855 again, I converted the policy template into a markdown block, because when this template (previously) get rendered into a webpage, copy-pasting completely loses the markdown formatting. Instead, present the policy template as a markdown codeblock (raw markdown annotations) so pasting it into e.g. an MCP will become properly formatted.