doc/sphinx/hxtool.py: add optional label argument to SRST directive

We can't just embed labels directly into files like qemu-options.hx which
are included from multiple top-level rST files, because Sphinx sees the
labels as duplicate: https://github.com/sphinx-doc/sphinx/issues/9707

So add an optional argument to the SRST directive which causes a label
of the form '.. _DOCNAME-HXFILE-LABEL:' to be emitted, where 'DOCNAME'
is the name of the top level rST file, 'HXFILE' is the filename of the
.hx file, and 'LABEL' is the text provided within the 'SRST()' directive.
Using the DOCNAME of the top-level rST document means that it is unique
even when the .hx file is included from two different documents, as is
the case for qemu-options.hx

Now where the Xen PV documentation refers to the documentation for the
-initrd command line option, it can emit a link directly to it as
'<system/invocation-qemu-options-initrd>'.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20240130190348.682912-1-dwmw2@infradead.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

docs/sphinx/hxtool.py

@@ -78,6 +78,14 @@ def parse_archheading(file, lnum, line):
         serror(file, lnum, "Invalid ARCHHEADING line")
     return match.group(1)
 
+def parse_srst(file, lnum, line):
+    """Handle an SRST directive"""
+    # The input should be either "SRST", or "SRST(label)".
+    match = re.match(r'SRST(\((.*?)\))?', line)
+    if match is None:
+        serror(file, lnum, "Invalid SRST line")
+    return match.group(2)
+
 class HxtoolDocDirective(Directive):
     """Extract rST fragments from the specified .hx file"""
     required_argument = 1
@@ -113,6 +121,14 @@ class HxtoolDocDirective(Directive):
                         serror(hxfile, lnum, 'expected ERST, found SRST')
                     else:
                         state = HxState.RST
+                        label = parse_srst(hxfile, lnum, line)
+                        if label:
+                            rstlist.append("", hxfile, lnum - 1)
+                            # Build label as _DOCNAME-HXNAME-LABEL
+                            hx = os.path.splitext(os.path.basename(hxfile))[0]
+                            refline = ".. _" + env.docname + "-" + hx + \
+                                "-" + label + ":"
+                            rstlist.append(refline, hxfile, lnum - 1)
                 elif directive == 'ERST':
                     if state == HxState.CTEXT:
                         serror(hxfile, lnum, 'expected SRST, found ERST')