CI: verify libcurl function SYNPOSIS sections

With the .github/scripits/verify-synopsis.pl script

Closes #12402

.github/scripts/verify-synopsis.pl

@@ -0,0 +1,81 @@
+#!/usr/bin/env perl
+#***************************************************************************
+#                                  _   _ ____  _
+#  Project                     ___| | | |  _ \| |
+#                             / __| | | | |_) | |
+#                            | (__| |_| |  _ <| |___
+#                             \___|\___/|_| \_\_____|
+#
+# Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
+#
+# This software is licensed as described in the file COPYING, which
+# you should have received as part of this distribution. The terms
+# are also available at https://curl.se/docs/copyright.html.
+#
+# You may opt to use, copy, modify, merge, publish, distribute and/or sell
+# copies of the Software, and permit persons to whom the Software is
+# furnished to do so, under the terms of the COPYING file.
+#
+# This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+# KIND, either express or implied.
+#
+# SPDX-License-Identifier: curl
+#
+###########################################################################
+
+my @files = @ARGV;
+my $cfile = "test.c";
+
+if($files[0] eq "-h") {
+    print "Usage: verify-synopsis [man pages]\n";
+    exit;
+}
+
+sub testcompile {
+    my $rc = system("gcc -c test.c -DCURL_DISABLE_TYPECHECK -DCURL_ALLOW_OLD_MULTI_SOCKET -I include") >> 8;
+    return $rc;
+}
+
+
+sub extract {
+    my($f) = @_;
+    my $syn = 0;
+    my $l = 0;
+    my $iline = 0;
+    open(F, "<$f");
+    open(O, ">$cfile");
+    while(<F>) {
+        $iline++;
+        if(/^.SH SYNOPSIS/) {
+            $syn = 1
+        }
+        elsif($syn == 1) {
+            if(/^.nf/) {
+                $syn++;
+                print O "#line $iline \"$f\"\n";
+            }
+        }
+        elsif($syn == 2) {
+            if(/^.fi/) {
+                last;
+            }
+            # turn the vararg argument into vararg
+            $_ =~ s/, parameter\)\;/, ...);/;
+            print O $_;
+            $l++;
+        }
+    }
+    close(F);
+    close(O);
+
+    return 0;
+}
+
+my $error;
+for my $m (@files) {
+    print "Verify $m\n";
+    extract($m);
+    $error |= testcompile($m);
+}
+exit $error;
+

.github/workflows/synopsis.yml

@@ -0,0 +1,28 @@
+# Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
+#
+# SPDX-License-Identifier: curl
+
+name: SYNOPSIS
+
+on:
+  push:
+    branches:
+    - master
+    - '*/ci'
+    paths:
+    - 'docs/libcurl/curl_*.3'
+  pull_request:
+    branches:
+    - master
+    paths:
+    - 'docs/libcurl/curl_*.3'
+
+jobs:
+  verify:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+
+      - name: verify-synopsis
+        run: ./.github/scripts/verify-synopsis.pl docs/libcurl/curl*.3