ci: Merge similar try jobs when possible (#31347)

* ci: Merge similar try jobs when possible

This comes up a lot when triggering wpt-2013 and wpt-2020. Instead of
merging the jobs and triggering both layouts, the try parser will
trigger two separate jobs. Running two of the same builds at once seems
to cause the CI to fail one of them [1]. This fixes that issue.

1. An example of this: https://github.com/servo/servo/actions/runs/7892269495

* Use a list of fields for merge compatability and add more tests

* Switch from comments to assert messages

* Update python/servo/try_parser.py

Co-authored-by: Samson <16504129+sagudev@users.noreply.github.com>

* Remote 'Ditto'

Co-authored-by: Samson <16504129+sagudev@users.noreply.github.com>

---------

Co-authored-by: Samson <16504129+sagudev@users.noreply.github.com>

python/servo/try_parser.py

@@ -9,9 +9,11 @@
 # option. This file may not be copied, modified, or distributed
 # except according to those terms.
 
+from __future__ import annotations
+
 import json
 import sys
-from typing import Optional
+from typing import ClassVar, List, Optional
 import unittest
 import logging
 
@@ -40,10 +42,10 @@ def to_string(self):
 
 
 class Workflow(str, Enum):
-    LINUX = 'linux'
-    MACOS = 'macos'
-    WINDOWS = 'windows'
-    ANDROID = 'android'
+    LINUX = "linux"
+    MACOS = "macos"
+    WINDOWS = "windows"
+    ANDROID = "android"
 
 
 @dataclass
@@ -54,6 +56,20 @@ class JobConfig(object):
     profile: str = "release"
     unit_tests: bool = False
     wpt_tests_to_run: str = ""
+    # These are the fields that must match in between two JobConfigs for them to be able to be
+    # merged. If you modify any of the fields above, make sure to update this line as well.
+    merge_compatibility_fields: ClassVar[List[str]] = ['workflow', 'profile', 'wpt_tests_to_run']
+
+    def merge(self, other: JobConfig) -> bool:
+        """Try to merge another job with this job. Returns True if merging is successful
+           or False if not. If merging is successful this job will be modified."""
+        for field in self.merge_compatibility_fields:
+            if getattr(self, field) != getattr(other, field):
+                return False
+
+        self.wpt_layout |= other.wpt_layout
+        self.unit_tests |= other.unit_tests
+        return True
 
 
 def handle_preset(s: str) -> Optional[JobConfig]:
@@ -68,15 +84,15 @@ def handle_preset(s: str) -> Optional[JobConfig]:
     elif s in ["wpt", "linux-wpt"]:
         return JobConfig("Linux WPT", Workflow.LINUX, unit_tests=True, wpt_layout=Layout.all())
     elif s in ["wpt-2013", "linux-wpt-2013"]:
-        return JobConfig("Linux WPT legacy-layout", Workflow.LINUX, wpt_layout=Layout.layout2013)
+        return JobConfig("Linux WPT", Workflow.LINUX, wpt_layout=Layout.layout2013)
     elif s in ["wpt-2020", "linux-wpt-2020"]:
-        return JobConfig("Linux WPT layout-2020", Workflow.LINUX, wpt_layout=Layout.layout2020)
+        return JobConfig("Linux WPT", Workflow.LINUX, wpt_layout=Layout.layout2020)
     elif s in ["mac-wpt", "wpt-mac"]:
         return JobConfig("MacOS WPT", Workflow.MACOS, wpt_layout=Layout.all())
     elif s == "mac-wpt-2013":
-        return JobConfig("MacOS WPT legacy-layout", Workflow.MACOS, wpt_layout=Layout.layout2013)
+        return JobConfig("MacOS WPT", Workflow.MACOS, wpt_layout=Layout.layout2013)
     elif s == "mac-wpt-2020":
-        return JobConfig("MacOS WPT layout-2020", Workflow.MACOS, wpt_layout=Layout.layout2020)
+        return JobConfig("MacOS WPT", Workflow.MACOS, wpt_layout=Layout.layout2020)
     elif s == "android":
         return JobConfig("Android", Workflow.ANDROID)
     elif s == "webgpu":
@@ -122,11 +138,17 @@ def parse(self, input: str):
                 words.extend(["linux-wpt", "macos", "windows", "android"])
                 continue  # skip over keyword
 
-            preset = handle_preset(word)
-            if preset is None:
+            job = handle_preset(word)
+            if job is None:
                 print(f"Ignoring unknown preset {word}")
             else:
-                self.matrix.append(preset)
+                self.add_or_merge_job_to_matrix(job)
+
+    def add_or_merge_job_to_matrix(self, job: JobConfig):
+        for existing_job in self.matrix:
+            if existing_job.merge(job):
+                return
+        self.matrix.append(job)
 
     def to_json(self, **kwargs) -> str:
         return json.dumps(self, cls=Encoder, **kwargs)
@@ -192,6 +214,39 @@ def test_empty(self):
                               }
                               ]})
 
+    def test_job_merging(self):
+        self.assertDictEqual(json.loads(Config("wpt-2020 wpt-2013").to_json()),
+                             {'fail_fast': False,
+                              'matrix': [{
+                                  'name': 'Linux WPT',
+                                  'profile': 'release',
+                                  'unit_tests': False,
+                                  'workflow': 'linux',
+                                  'wpt_layout': 'all',
+                                  'wpt_tests_to_run': ''
+                              }]
+                              })
+
+        a = JobConfig("Linux", Workflow.LINUX, unit_tests=True)
+        b = JobConfig("Linux", Workflow.LINUX, unit_tests=False)
+        self.assertTrue(a.merge(b), "Should not merge jobs that have different unit test configurations.")
+        self.assertEqual(a, JobConfig("Linux", Workflow.LINUX, unit_tests=True))
+
+        a = JobConfig("Linux", Workflow.LINUX, unit_tests=True)
+        b = JobConfig("Mac", Workflow.MACOS, unit_tests=True)
+        self.assertFalse(a.merge(b), "Should not merge jobs with different workflows.")
+        self.assertEqual(a, JobConfig("Linux", Workflow.LINUX, unit_tests=True))
+
+        a = JobConfig("Linux", Workflow.LINUX, unit_tests=True)
+        b = JobConfig("Linux", Workflow.LINUX, unit_tests=True, profile="production")
+        self.assertFalse(a.merge(b), "Should not merge jobs with different profiles.")
+        self.assertEqual(a, JobConfig("Linux", Workflow.LINUX, unit_tests=True))
+
+        a = JobConfig("Linux", Workflow.LINUX, unit_tests=True)
+        b = JobConfig("Linux", Workflow.LINUX, unit_tests=True, wpt_tests_to_run="/css")
+        self.assertFalse(a.merge(b), "Should not merge jobs that run different WPT tests.")
+        self.assertEqual(a, JobConfig("Linux", Workflow.LINUX, unit_tests=True))
+
     def test_full(self):
         self.assertDictEqual(json.loads(Config("linux-wpt macos windows android").to_json()),
                              json.loads(Config("").to_json()))