Document how to write configs for iOS bots

docs/ios_infra.md

 # Continuous build and test infrastructure for Chromium for iOS
 
 See the [instructions] for how to check out and build Chromium for iOS.
 
 The Chromium projects use buildbot for continuous integration. This doc starts
 with an overview of the system, then gives detailed explanations about each
 part.
 
 [TOC]
 
@@ skipping 100 matching lines @@
 requests which they execute and post the results of.
 
 ### Compiling with the analyzer
 
 In addition to goma, the try bots use another time-saving mechanism called the
 [analyzer] to determine the subset of compilation targets affected by the patch
 that need to be compiled in order to run the affected tests. If a patch is
 determined not to affect a certain test target, compilation and execution of the
 test target will be skipped.
 
+## Configuring the bots
+
+See the [configs code location](#Configs) for where to find the config files for
+the bots. The config files are JSON which describe how the bot should compile
+and which tests it should run. The config files are located in the configs
+directory. The configs directory contains a named directory for each master. For
+example:
+```shell
+$ ls ios/build/bots
+OWNERS  scripts  tests  chromium.fyi  chromium.mac
+```
+In this case, configs are defined for iOS bots on [chromium.fyi] and
+[chromium.mac]. Inside each master-specific directory are JSON config files
+named after each bot. For example:
+```shell
+$ ls ios/build/bots/chromium.mac
+ios-device.json ios-simulator.json
+```
+The `ios-device` bot on [chromium.mac] will read its configuration from
+`chromium.mac/ios-device.json` in the configs directory.
+
+### Example
+
+```json
+{
+  "comments": [
+    "Sample config for a bot."
+  ],
+  "gn_args": [
+    "is_debug=true",
+    "target_cpu=\"x64\""
+  ],
+  "tests": [
+    {
+      "app": "ios_chrome_unittests",
+      "device type": "iPhone 5s",
+      "os": "10.0",
+      "xcode version": "8.0"
+    }
+  ]
+}
+```
+The `comments` key is optional and defines a list of strings which can be used
+to annotate the config. You may want to explain why the bot exists and what it's
+doing, particularly if there are extensive and atypical `gn_args`.
+
+The `gn_args` key is a required list of arguments to pass to [GN] to generate
+the build files. Two GN args are required, `is_debug` and `target_cpu`. Use
+`is_debug` to define whether to compile for Debug or Release, and `target_cpu`
+to define whether to compile for x86, x64, arm, or arm64. The iOS bots typically
+perform Debug builds for x86 and x64, and Release builds for arm and arm64. An
+x86/x64 build can only be tested on the [iOS simulator], while an arm/arm64
+build can only be tested on a physical device.
+
+Since Chromium for iOS is shipped as a [universal binary], it's also fairly
+common to set `additional_target_cpus`. For simulator builds, we typically set:
+```json
+"gn_args": [
+  "additional_target_cpus=[\"x86\"]",
+  "is_debug=true",
+  "target_cpu=\"x64\""
+]
+```
+This builds universal binaries which run in 32-bit mode on 32-bit simulators and
+64-bit mode on 64-bit simulators. For device builds we typically set:
+```json
+"gn_args": [
+  "additional_target_cpus=[\"arm\"]",
+  "is_debug=false",
+  "target_cpu=\"arm64\""
+]
+```
+In order to build universal binaries which run in 32-bit mode on 32-bit devices
+and 64-bit mode on 64-bit devices.
+
+The `tests` key is an optional list of dictionaries defining tests to run. There
+are two types of test dictionary, `app` and `include`. An `app` dict defines a
+specific compiled app to run, for example:
+```json
+"tests": [
+  {
+    "app": "ios_chrome_unittests",
+    "device type": "iPhone 5s",
+    "os": "10.0",
+    "xcode version": "8.0"
+  }
+]
+```
+This dict says to run `ios_chrome_unittests` on an `iPhone 5s` running iOS
+`10.0` using Xcode `8.0`. A test dict may optionally define a list of `test
+args`, which are arguments to pass directly to the test on the command line,
+and it may define a boolean value `xctest` to indicate whether the test is an
+[xctest] \(default if unspecified is `false`\). For example:
+```json
+"tests": [
+  {
+    "app": "ios_chrome_unittests",
+    "device type": "iPhone 5s",
+    "os": "10.0",
+    "test args": [
+      "--foo",
+      "--bar"
+    ],
+    "xcode version": "8.0"
+  },
+  {
+    "app": "ios_chrome_integration_egtests",
+    "device type": "iPhone 5s",
+    "os": "10.0",
+    "xcode version": "8.0",
+    "xctest": true
+  }
+]
+```
+This defines two tests to run, first `ios_chrome_unittests` will be run with
+`--foo` and `--bar` passed directly to the test on the command line. Next,
+`ios_chrome_integration_egtests` will be run as an xctest. `"xctest": true`
+must be specified for all xctests, it is an error to try and launch an xctest as
+a regular test.
+
+An `include` dict defines a list of tests to import from the `tests`
+subdirectory in the configs directory. For example:
+```json
+"tests": [
+  {
+    "include": "common_tests.json",
+    "device type": "iPhone 5s",
+    "os": "10.0",
+    "xcode version": "8.0"
+  }
+]
+```
+This dict says to import the list of tests from the `tests` subdirectory and run
+each one on an `iPhone 5s` running iOS `10.0` using Xcode `8.0`. Here's what
+`common_tests.json` might look like:
+```json
+"tests": [
+  {
+    "app": "ios_chrome_unittests"
+  },
+  {
+    "app": "ios_net_unittests"
+  },
+  {
+    "app": "ios_web_unittests"
+  },
+]
+```
+Includes may contain other keys besides `app` which can then be omitted in the
+bot config. For example if `common_tests.json` specifies:
+```json
+"tests": [
+  {
+    "app": "ios_chrome_integration_egtests",
+    "xctest": true,
+    "xcode version": "8.0"
+  }
+]
+```
+Then the bot config may omit the `xctest` or `xcode version` keys, for example:
+```json
+{
+  "comments": [
+    "Sample config for a bot."
+  ],
+  "gn_args": [
+    "is_debug=true",
+    "target_cpu=\"x64\""
+  ],
+  "tests": [
+    {
+      "include": "common_tests.json",
+      "device type": "iPhone 5s",
+      "os": "10.0"
+    }
+  ]
+}
+```
+Includes are not recursive, so `common_tests.json` may not itself include any
+`include` dicts.
+
+### Uploading compiled artifacts from a bot
+
+A bot may be configured to upload compiled artifacts. This is defined by the
+`upload` key. For example:
+```json
+{
+  "comments": [
+    "Sample config for a bot which uploads artifacts."
+  ],
+  "gn_args": [
+    "is_debug=true",
+    "target_cpu=\"x64\""
+  ],
+  "upload": [
+    {
+      "artifact": "Chromium.breakpad",
+      "bucket": "my-gcs-bucket",
+    },
+    {
+      "artifact": "Chromium.app",
+      "bucket": "my-gcs-bucket",
+      "compress": true,
+    },
+    {
+      "artifact": "Chromium.breakpad",
+      "symupload": true,
+    }
+  ]
+}
+```
+After compilation, the bot will upload three artifacts. First the
+`Chromium.breakpad` symbols will be uploaded to
+`gs://my-gcs-bucket/<buildername>/<buildnumber>/Chromium.breakpad`. Next
+`Chromium.app` will be tarred, gzipped, and uploaded to
+`gs://my-gcs-bucket/<buildername>/<buildnumber>/Chromium.tar.gz`. Finally
+the `Chromium.breakpad` symbols will be uploaded to the [breakpad] crash
+reporting server where they can be used to symbolicate stack traces.
+
+If `artifact` is a directory, you must specify `"compress": true`.
+
 [analyzer]: ../tools/mb
+[breakpad]: https://chromium.googlesource.com/breakpad/breakpad
 [buildbucket]: https://cr-buildbucket.appspot.com
+[chromium.fyi]: https://build.chromium.org/p/chromium.fyi/waterfall
 [chromium.mac]: https://build.chromium.org/p/chromium.mac
 [clang]: ../tools/clang
 [commit queue]: https://dev.chromium.org/developers/testing/commit-queue
 [gitiles]: https://gerrit.googlesource.com/gitiles
+[GN]: ../tools/gn
 [instructions]: ./ios_build_instructions.md
 [iOS recipes]: https://chromium.googlesource.com/chromium/tools/build/+/master/scripts/slave/recipes/ios
+[iOS simulator]: ../testing/iossim
 [recipe module]: https://chromium.googlesource.com/chromium/tools/build/+/master/scripts/slave/recipe_modules/ios
 [recipes]: https://chromium.googlesource.com/infra/infra/+/HEAD/doc/users/recipes.md
 [simulator]: https://developer.apple.com/library/content/documentation/IDEs/Conceptual/iOS_Simulator_Guide/Introduction/Introduction.html
 [src/ios/build/bots]: ../ios/build/bots
 [src/ios/build/bots/scripts]: ../ios/build/bots/scripts
 [swarming]: https://github.com/luci/luci-py/tree/master/appengine/swarming
 [swarming server]: https://chromium-swarm.appspot.com
 [test runner]: ../ios/build/bots/scripts/test_runner.py
 [tools/build]: https://chromium.googlesource.com/chromium/tools/build
 [try job access]: https://www.chromium.org/getting-involved/become-a-committer#TOC-Try-job-access
 [try server]: https://build.chromium.org/p/tryserver.chromium.mac/waterfall
 [tryserver.chromium.mac]: https://build.chromium.org/p/tryserver.chromium.mac/waterfall
+[universal binary]: https://en.wikipedia.org/wiki/Universal_binary
+[xctest]: https://developer.apple.com/reference/xctest