Support overriding services for tests

azure/coverage.yml

@@ -1,5 +1,6 @@
 parameters:
   envs: {}
+  services: {}
   setup: []
   submodules: recursive
   nightly: false
@@ -10,6 +11,14 @@ jobs:
    displayName: tarpaulin
    pool:
      vmImage: ubuntu-16.04
+   # this is sad: we need to spin up the service containers even if the token
+   # isn't set, since we can't set a service in a particular script step.
+   # once the fix to
+   # https://developercommunity.visualstudio.com/content/problem/642219/setting-output-variable-when-multiple-stages-share.html
+   # lands everywhere, we can move to multiple jobs instead, and then only the
+   # (conditional) second job will have this service.
+   services:
+     ${{ insert }}: ${{ parameters.services }}
    continueOnError: ${{ parameters.nightly }}
    container:
      ${{ if eq('true', parameters.nightly) }}:

azure/test.yml

@@ -7,6 +7,7 @@ parameters:
   test_ignored: false
   single_threaded: false
   features: '' # empty feature list is == default
+  services: {}
 
 jobs:
 - job: ${{ parameters.name }}
@@ -29,6 +30,8 @@ jobs:
       vmImage: ubuntu-16.04
   pool:
     vmImage: $(vmImage)
+  services:
+    ${{ insert }}: ${{ parameters.services }}
   steps:
   - template: _setup.yml
     parameters:

docs/custom.md

@@ -175,6 +175,8 @@ parameters:
   features: <string> = ''
   envs:
     NAME: value
+  services:
+    NAME: container
   setup:
     - task
 ```
@@ -192,6 +194,10 @@ set `test_ignored: true`. To run tests with
 [`--test-threads=1`](https://doc.rust-lang.org/book/ch11-02-running-tests.html#running-tests-in-parallel-or-consecutively),
 set `single_threaded: true`. To run tests with particular features
 enabled, pass `features: "feat1,feat2,subcrate/feat3"`.
+To spin up additional [service
+containers](https://docs.microsoft.com/en-us/azure/devops/pipelines/process/service-containers?view=azure-devops&tabs=yaml),
+pass them in `services` (though note that these will generally only work
+on Linux, so `cross: true` likely won't work).
 
 ### Style
 
@@ -235,8 +241,10 @@ and upload the coverage test results to
 `codecov_token` that includes the codecov.io upload token (see the
 [setup instructions](setup.md#code-coverage)). You can also pass the
 parameter `envs: {...}` to pass [environment
-variables](configuration.md#environment-variables), and `setup: [...]`
-to run [additional setup
+variables](configuration.md#environment-variables), `services: {...}` to
+run additional [service
+containers](https://docs.microsoft.com/en-us/azure/devops/pipelines/process/service-containers?view=azure-devops&tabs=yaml),
+and `setup: [...]` to run [additional setup
 steps](configuration.md#additional-setup-steps).
 
 By default, your pipeline will test against the stable Rust version