ci: Add a way to run libm tests that would otherwise be skipped

As part of this, commonize the way to get a `PrInfo` object from
environment variables.

Author: tgross35

ci/ci-util.py

@@ -59,6 +59,8 @@
 # accidentally spending huge amounts of CI time.
 ALLOW_MANY_EXTENSIVE_DIRECTIVE = "ci: allow-many-extensive"
 MANY_EXTENSIVE_THRESHOLD = 20
+# Require tests for `libm`
+TEST_LIBM_DIRECTIVE = "ci: test-libm"
 
 # Don't run exhaustive tests if these files change, even if they contaiin a function
 # definition.
@@ -90,8 +92,17 @@ class PrInfo:
     number: int
 
     @classmethod
-    def load(cls, pr_number: int | str) -> Self:
-        """For a given PR number, query the body and commit list"""
+    def from_env(cls) -> Self | None:
+        """Create a PR object from the PR_NUMBER environment if set, `None` otherwise."""
+        pr_env = os.environ.get("PR_NUMBER")
+        if pr_env is not None and len(pr_env) > 0:
+            return cls.from_pr(pr_env)
+
+        return None
+
+    @classmethod
+    def from_pr(cls, pr_number: int | str) -> Self:
+        """For a given PR number, query the body and commit list."""
         pr_info = sp.check_output(
             [
                 "gh",
@@ -207,22 +218,31 @@ def may_skip_libm_ci(self) -> bool:
         """If this is a PR and no libm files were changed, allow skipping libm
         jobs."""
 
-        if self.is_pr():
-            return all(not re.match(TRIGGER_LIBM_PR_CI, str(f)) for f in self.changed)
+        # Always run on merge CI
+        if not self.is_pr():
+            return False
+
+        pr = PrInfo.from_env()
+        if pr is None:
+            eprint("Is a PR but couldn't load PrInfo")
+            exit(1)
+
+        # Allow opting in to libm tests
+        if pr.contains_directive(TEST_LIBM_DIRECTIVE):
+            return True
 
-        return False
+        return all(not re.match(TRIGGER_LIBM_PR_CI, str(f)) for f in self.changed)
 
     def emit_workflow_output(self):
         """Create a JSON object a list items for each type's changed files, if any
         did change, and the routines that were affected by the change.
         """
 
-        pr_number = os.environ.get("PR_NUMBER")
         skip_tests = False
         error_on_many_tests = False
 
-        if pr_number is not None and len(pr_number) > 0:
-            pr = PrInfo.load(pr_number)
+        pr = PrInfo.from_env()
+        if pr is not None:
             skip_tests = pr.contains_directive(SKIP_EXTENSIVE_DIRECTIVE)
             error_on_many_tests = not pr.contains_directive(
                 ALLOW_MANY_EXTENSIVE_DIRECTIVE
@@ -371,7 +391,7 @@ def handle_bench_regressions(args: list[str]):
             eprint(USAGE)
             exit(1)
 
-    pr = PrInfo.load(pr_number)
+    pr = PrInfo.from_pr(pr_number)
     if pr.contains_directive(REGRESSION_DIRECTIVE):
         eprint("PR allows regressions")
         return