CI: skip qemu matrix for documentation-only pull requests

Add a new "docs" CI type, selected when every file modified by a
pull request matches a documentation pattern (man pages, .md,
AUTHORS, COPYRIGHT, LICENSE, NOTICE, .gitignore). For this type the
os_selection is empty and the qemu matrix runs no jobs.

This affects only pull requests whose entire diff is documentation.
Any change touching a non-documentation file continues to be
classified as full, quick, linux, or freebsd by the existing
file-path rules, and a manual ZFS-CI-Type commit tag still overrides
that classification.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Christos Longros <chris.longros@gmail.com>
Closes #18518

.github/workflows/scripts/generate-ci-type.py

@@ -6,6 +6,9 @@
 Output format: "<type> <source>" where source is "manual" (from
 ZFS-CI-Type commit tag) or "auto" (from file change heuristics).
 
+Prints "docs auto" if every changed file is documentation; the qemu
+matrix is skipped in that case.
+
 Prints "quick manual" if:
 - the *last* commit message contains 'ZFS-CI-Type: quick'
 or "quick auto" if (heuristics):
@@ -28,6 +31,19 @@
     r'.*\.gitignore'
 ]))
 
+"""
+Patterns of files that are documentation only.
+"""
+DOCS_ONLY_REGEX = list(map(re.compile, [
+    r'man/.*',
+    r'.*\.md',
+    r'AUTHORS',
+    r'COPYRIGHT',
+    r'LICENSE',
+    r'NOTICE',
+    r'\.gitignore',
+]))
+
 """
 Patterns of files that are considered to trigger full CI.
 """
@@ -116,6 +132,12 @@ def output_type(type, source, reason):
                         f'changed file "{f}" matches pattern "{r.pattern}"'
                         )
 
+    if changed_files and all(
+            any(r.match(f) for r in DOCS_ONLY_REGEX)
+            for f in changed_files):
+        output_type('docs', 'auto',
+                    'all changed files are documentation')
+
     # catch-all
     output_type('quick', 'auto',
                 'no changed file matches full CI patterns')

.github/workflows/zfs-qemu.yml

@@ -45,6 +45,9 @@ jobs:
           fi
 
           case "$ci_type" in
+          docs)
+            os_selection='[]'
+            ;;
           quick)
             os_selection='["almalinux8", "almalinux9", "almalinux10", "debian12", "fedora42", "freebsd15-1s", "ubuntu24"]'
             ;;
@@ -91,6 +94,7 @@ jobs:
   qemu-vm:
     name: qemu-x86
     needs: [ test-config ]
+    if: needs.test-config.outputs.ci_type != 'docs'
     strategy:
       fail-fast: false
       matrix: