gh-37738: CI Build&Test: Show segfaults using GitHub annotations
    
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Expanding the feature
https://github.com/sagemath/sage/wiki/Sage-10.3-Release-Tour#doctest-
failures-are-shown-in-the-files-changed-tab-on-prs
to cover doctests that crash the doctest runner.

An example (https://github.com/sagemath/sage/pull/37709/files)
<img width="1078" alt="Screenshot 2024-04-03 at 11 14 05 AM"
src="https://github.com/sagemath/sage/assets/8345221/de990f1f-069c-4fcf-
ac7e-ed915687533b">


### 📝 Checklist

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- [x] The description explains in detail what this PR is about.
- [ ] I have linked a relevant issue or discussion.
- [ ] I have created tests covering the changes.
- [ ] I have updated the documentation accordingly.

### ⌛ Dependencies

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URL: #37738
Reported by: Matthias Köppe
Reviewer(s): Kwankyu Lee

Author: Release Manager

src/sage/doctest/reporting.py

@@ -41,6 +41,7 @@
 #                  https://www.gnu.org/licenses/
 # ****************************************************************************
 
+import re
 from sys import stdout
 from signal import (SIGABRT, SIGALRM, SIGBUS, SIGFPE, SIGHUP, SIGILL,
                     SIGINT, SIGKILL, SIGPIPE, SIGQUIT, SIGSEGV, SIGTERM)
@@ -218,6 +219,69 @@ def report_head(self, source, fail_msg=None):
                 cmd += f" [failed in baseline: {failed}]"
         return cmd
 
+    def _log_failure(self, source, fail_msg, event, output=None):
+        r"""
+        Report on the result of a failed doctest run.
+
+        INPUT:
+
+        - ``source`` -- a source from :mod:`sage.doctest.sources`
+
+        - ``fail_msg`` -- a string
+
+        - ``event`` -- a string
+
+        - ``output`` -- optional string
+
+        EXAMPLES::
+
+            sage: from sage.doctest.reporting import DocTestReporter
+            sage: from sage.doctest.control import DocTestController, DocTestDefaults
+            sage: from sage.doctest.sources import FileDocTestSource
+            sage: from sage.env import SAGE_SRC
+            sage: import os
+            sage: filename = os.path.join(SAGE_SRC, 'sage', 'doctest', 'reporting.py')
+            sage: DD = DocTestDefaults()
+            sage: FDS = FileDocTestSource(filename, DD)
+            sage: DC = DocTestController(DD,[filename])
+            sage: DTR = DocTestReporter(DC)
+            sage: DTR._log_failure(FDS, "Timed out", "process (pid=1234) timed out", "Output so far...")
+                Timed out
+            **********************************************************************
+            Tests run before process (pid=1234) timed out:
+            Output so far...
+            **********************************************************************
+        """
+        log = self.controller.log
+        format = self.controller.options.format
+        if format == 'sage':
+            stars = "*" * 70
+            log(f"    {fail_msg}\n{stars}\n")
+            if output:
+                log(f"Tests run before {event}:")
+                log(output)
+                log(stars)
+        elif format == 'github':
+            # https://docs.github.com/en/actions/using-workflows/workflow-commands-for-github-actions#using-workflow-commands-to-access-toolkit-functions
+            command = f'::error title={fail_msg}'
+            command += f',file={source.printpath}'
+            if output:
+                if m := re.search("## line ([0-9]+) ##\n-{40,100}\n(.*)", output, re.MULTILINE | re.DOTALL):
+                    lineno = m.group(1)
+                    message = m.group(2)
+                    command += f',line={lineno}'
+                else:
+                    message = output
+                # Urlencoding trick for multi-line annotations
+                # https://github.com/actions/starter-workflows/issues/68#issuecomment-581479448
+                message = message.replace('\n', '%0A')
+            else:
+                message = ""
+            command += f'::{message}'
+            log(command)
+        else:
+            raise ValueError(f'unknown format option: {format}')
+
     def report(self, source, timeout, return_code, results, output, pid=None):
         """
         Report on the result of running doctests on a given source.
@@ -435,9 +499,7 @@ def report(self, source, timeout, return_code, results, output, pid=None):
                         fail_msg += " (and interrupt failed)"
                     else:
                         fail_msg += " (with %s after interrupt)" % signal_name(sig)
-                log("    %s\n%s\nTests run before %s timed out:" % (fail_msg, "*"*70, process_name))
-                log(output)
-                log("*"*70)
+                self._log_failure(source, fail_msg, f"{process_name} timed out", output)
                 postscript['lines'].append(self.report_head(source, fail_msg))
                 stats[basename] = {"failed": True, "walltime": 1e6, "ntests": ntests}
                 if not baseline.get('failed', False):
@@ -449,9 +511,7 @@ def report(self, source, timeout, return_code, results, output, pid=None):
                     fail_msg = "Killed due to %s" % signal_name(-return_code)
                 if ntests > 0:
                     fail_msg += " after testing finished"
-                log("    %s\n%s\nTests run before %s failed:" % (fail_msg,"*"*70, process_name))
-                log(output)
-                log("*"*70)
+                self._log_failure(source, fail_msg, f"{process_name} failed", output)
                 postscript['lines'].append(self.report_head(source, fail_msg))
                 stats[basename] = {"failed": True, "walltime": 1e6, "ntests": ntests}
                 if not baseline.get('failed', False):
@@ -466,15 +526,11 @@ def report(self, source, timeout, return_code, results, output, pid=None):
                 else:
                     cpu = 1e6
                 if result_dict.err == 'badresult':
-                    log("    Error in doctesting framework (bad result returned)\n%s\nTests run before error:" % ("*"*70))
-                    log(output)
-                    log("*"*70)
+                    self._log_failure(source, "Error in doctesting framework (bad result returned)", "error", output)
                     postscript['lines'].append(self.report_head(source, "Testing error: bad result"))
                     self.error_status |= 64
                 elif result_dict.err == 'noresult':
-                    log("    Error in doctesting framework (no result returned)\n%s\nTests run before error:" % ("*"*70))
-                    log(output)
-                    log("*"*70)
+                    self._log_failure(source, "Error in doctesting framework (no result returned)", "error", output)
                     postscript['lines'].append(self.report_head(source, "Testing error: no result"))
                     self.error_status |= 64
                 elif result_dict.err == 'tab':
@@ -500,11 +556,7 @@ def report(self, source, timeout, return_code, results, output, pid=None):
                         else:
                             err = repr(result_dict.err)
                         fail_msg = "%s in doctesting framework" % err
-
-                    log("    %s\n%s" % (fail_msg, "*"*70))
-                    if output:
-                        log("Tests run before doctest exception:\n" + output)
-                        log("*"*70)
+                    self._log_failure(source, fail_msg, "exception", output)
                     postscript['lines'].append(self.report_head(source, fail_msg))
                     if hasattr(result_dict, 'tb'):
                         log(result_dict.tb)