operation docs: extract from doc strings

Use the class docstring plus the parameter list from the filter_func.

docs/ext/operations_user_doc.py

@@ -1,8 +1,13 @@
 # Copyright (C) 2021 ISIS Rutherford Appleton Laboratory UKRI
 # SPDX - License - Identifier: GPL-3.0-or-later
 
+from typing import List
+
 from docutils import nodes
+from docutils.nodes import Node
+from docutils.statemachine import ViewList
 from docutils.parsers.rst import Directive
+from sphinx.util.nodes import nested_parse_with_titles
 """Custom extension to add nicely formatted documentation for the operations.
 
 Use:
@@ -12,20 +17,71 @@
 """
 
 
+def make_heading(s: str, char: str) -> List[str]:
+    return [s, len(s) * char, ""]
+
+
+def split_lines(s: str) -> List[str]:
+    s = s.replace("\n\n", "DOUBLE_NEW_LINE")
+    s = s.replace("\n", " ")
+    s = s.replace("DOUBLE_NEW_LINE", "\n\n")
+    return s.split("\n")
+
+
+PARAM_SKIP_LIST = ["images", "cores", "chunksize", "progress"]
+
+
+def get_params(s: str) -> List[str]:
+    ret = []
+    for line in s.split("\n"):
+        if line.strip().startswith(":param"):
+            param_name = line.strip().split()[1].strip(':')
+            if param_name in PARAM_SKIP_LIST:
+                continue
+            ret.append(line.strip())
+        elif line.strip().startswith(":return"):
+            pass
+        elif line.strip() and ret:
+            ret[-1] = ret[-1] + " " + line.strip()
+
+    return ret
+
+
 class OperationsUserDoc(Directive):
-    def run(self):
+    def run(self) -> List[Node]:
 
-        paragraphs = []
         try:
             from mantidimaging.core.operations.loader import load_filter_packages
         except ImportError:
             raise ValueError("operations_user_doc could not import load_filter_packages")
 
+        rst_lines = []
+
         operations = load_filter_packages()
         for op in operations:
-            paragraphs.append(nodes.paragraph(text=op.filter_name))
+            # Title
+            rst_lines += make_heading(op.filter_name, "-")
+
+            # Description from class doc string
+            rst_lines += split_lines(op.__doc__)
+            rst_lines.append("")
+
+            # parameters from filter_func
+            if op.filter_func.__doc__ is not None:
+                rst_lines += get_params(op.filter_func.__doc__)
+                rst_lines.append("")
+
+        rst = ViewList()
+        for n, rst_line in enumerate(rst_lines):
+            rst.append(rst_line, "generated.rst", n)
+            print(n, ">", rst_line)
+
+        node = nodes.section()
+        node.document = self.state.document
+
+        nested_parse_with_titles(self.state, rst, node)
 
-        return paragraphs
+        return node.children
 
 
 def setup(app):