[PATCH v2 21/21] qapi: remove "Example" doc section

[John Snow <jsnow@redhat.com>]

Fully eliminate the "Example" sections in QAPI doc blocks now that they
have all been converted to arbitrary rST syntax using the
".. qmp-example::" directive. Update tests to match.

Migrating to the new syntax
---------------------------

The old "Example:" or "Examples:" section syntax is now caught as an
error, but "Example::" is stil permitted as explicit rST syntax for an
un-lexed, generic preformatted text block.

('Example' is not special in this case, any sentence that ends with "::"
will start an indented code block in rST.)

Arbitrary rST for Examples are now possible, but it's strongly
recommended that documentation authors use the ".. qmp-example::"
directive for consistent visual formatting in rendered HTML docs. The
":title:" directive option may be used to add extra information into the
title bar for the example. The ":annotated:" option can be used to write
arbitrary rST instead, with nested "::" blocks applying QMP formatting
where desired.

Other choices available are ".. code-block:: QMP" which will not create
an "Example:" box, or the short-form "::" code-block syntax which will
not apply QMP highlighting when used outside of the qmp-example
directive.

Why?
----

This patch has several benefits:

1. Example sections can now be written more arbitrarily, mixing
   explanatory paragraphs and code blocks however desired.

2. Example sections can now use fully arbitrary rST.

3. All code blocks are now lexed and validated as QMP; increasing
   usability of the docs and ensuring validity of example snippets.

   (To some extent - This patch only gaurantees it lexes correctly, not
   that it's valid under the JSON or QMP grammars. It will catch most
   small mistakes, however.)

4. Each qmp-example can be titled or annotated independently without
   bypassing the QMP lexer/validator.

   (i.e. code blocks are now for *code* only, so we don't have to
   sacrifice exposition for having lexically valid examples.)

NOTE: As with the "Notes" conversion patch, this patch (and those
      preceding) may change the rendering order for Examples in the
      current generator. The forthcoming qapidoc rewrite will fix this
      by always generating documentation in source order.

Signed-off-by: John Snow <jsnow@redhat.com>
---
 docs/devel/qapi-code-gen.rst    | 15 +++++++--------
 scripts/qapi/parser.py          | 10 +++++++++-
 tests/qapi-schema/doc-good.json | 19 ++++++++++++-------
 tests/qapi-schema/doc-good.out  | 26 ++++++++++++++++++--------
 tests/qapi-schema/doc-good.txt  | 23 ++++++++++-------------
 5 files changed, 56 insertions(+), 37 deletions(-)

diff --git a/docs/devel/qapi-code-gen.rst b/docs/devel/qapi-code-gen.rst
index ae97b335cbf..493e2b8f8df 100644
--- a/docs/devel/qapi-code-gen.rst
+++ b/docs/devel/qapi-code-gen.rst
@@ -995,8 +995,8 @@ line "Features:", like this::
   # @feature: Description text
 
 A tagged section begins with a paragraph that starts with one of the
-following words: "Since:", "Example:"/"Examples:", "Returns:",
-"Errors:", "TODO:".  It ends with the start of a new section.
+following words: "Since:", "Returns:", "Errors:", "TODO:".  It ends with
+the start of a new section.
 
 The second and subsequent lines of tagged sections must be indented
 like this::
@@ -1020,10 +1020,9 @@ detailing a relevant error condition. For example::
 A "Since: x.y.z" tagged section lists the release that introduced the
 definition.
 
-An "Example" or "Examples" section is rendered entirely
-as literal fixed-width text.  "TODO" sections are not rendered at all
-(they are for developers, not users of QMP).  In other sections, the
-text is formatted, and rST markup can be used.
+"TODO" sections are not rendered at all (they are for developers, not
+users of QMP).  In other sections, the text is formatted, and rST markup
+can be used.
 
 For example::
 
@@ -1058,11 +1057,11 @@ For example::
  #
  # Since: 0.14
  #
- # Example:
+ # .. qmp-example::
  #
  #     -> { "execute": "query-blockstats" }
  #     <- {
- #          ... lots of output ...
+ #          ...
  #        }
  ##
  { 'command': 'query-blockstats',
diff --git a/scripts/qapi/parser.py b/scripts/qapi/parser.py
index 6ad5663e545..adc85b5b394 100644
--- a/scripts/qapi/parser.py
+++ b/scripts/qapi/parser.py
@@ -553,7 +553,7 @@ def get_doc(self) -> 'QAPIDoc':
                     # Note: "sections" with two colons are left alone as
                     # rST markup and not interpreted as a section heading.
 
-                    # TODO: Remove this error sometime in 2025 or so
+                    # TODO: Remove these errors sometime in 2025 or so
                     # after we've fully transitioned to the new qapidoc
                     # generator.
 
@@ -567,6 +567,14 @@ def get_doc(self) -> 'QAPIDoc':
                         )
                         raise QAPIParseError(self, emsg)
 
+                    if 'Example' in match.group(1):
+                        emsg = (
+                            f"The '{match.group(1)}' section is no longer "
+                            "supported. Please use the '.. qmp-example::' "
+                            "directive, or other suitable markup instead."
+                        )
+                        raise QAPIParseError(self, emsg)
+
                     doc.new_tagged_section(self.info, match.group(1))
                     text = line[match.end():]
                     if text:
diff --git a/tests/qapi-schema/doc-good.json b/tests/qapi-schema/doc-good.json
index 107123f8a8d..c71d65cd51f 100644
--- a/tests/qapi-schema/doc-good.json
+++ b/tests/qapi-schema/doc-good.json
@@ -172,12 +172,17 @@
 #
 #  Duis aute irure dolor
 #
-# Example:
+# .. qmp-example::
+#    :title: Ideal fast-food burger situation
 #
-#  -> in
-#  <- out
+#    -> "in"
+#    <- "out"
 #
-# Examples:
+# Examples::
+#
+#  - Not a QMP code block
+#  - Merely a preformatted code block literal
+#  It isn't even an rST list.
 #  - *verbatim*
 #  - {braces}
 #
@@ -199,11 +204,11 @@
 # @cmd-feat1: a feature
 # @cmd-feat2: another feature
 #
-# Example:
+# .. qmp-example::
 #
-#  -> in
+#    -> "this example"
 #
-#  <- out
+#    <- "has no title"
 ##
 { 'command': 'cmd-boxed', 'boxed': true,
   'data': 'Object',
diff --git a/tests/qapi-schema/doc-good.out b/tests/qapi-schema/doc-good.out
index bd876b6542d..eee18cd436a 100644
--- a/tests/qapi-schema/doc-good.out
+++ b/tests/qapi-schema/doc-good.out
@@ -184,13 +184,21 @@ frobnicate
  - Ut enim ad minim veniam
 
  Duis aute irure dolor
-    section=Example
- -> in
- <- out
-    section=Examples
+
+.. qmp-example::
+   :title: Ideal fast-food burger situation
+
+   -> "in"
+   <- "out"
+
+Examples::
+
+ - Not a QMP code block
+ - Merely a preformatted code block literal
+ It isn't even an rST list.
  - *verbatim*
  - {braces}
-    section=None
+
 Note::
    Ceci n'est pas une note
     section=Since
@@ -202,10 +210,12 @@ If you're bored enough to read this, go see a video of boxed cats
 a feature
     feature=cmd-feat2
 another feature
-    section=Example
- -> in
+    section=None
+.. qmp-example::
 
- <- out
+   -> "this example"
+
+   <- "has no title"
 doc symbol=EVT_BOXED
     body=
 
diff --git a/tests/qapi-schema/doc-good.txt b/tests/qapi-schema/doc-good.txt
index 30d457e5488..cb37db606a6 100644
--- a/tests/qapi-schema/doc-good.txt
+++ b/tests/qapi-schema/doc-good.txt
@@ -217,17 +217,16 @@ Notes:
 
 Duis aute irure dolor
 
+Example: Ideal fast-food burger situation:
 
-Example
-~~~~~~~
+   -> "in"
+   <- "out"
 
-   -> in
-   <- out
-
-
-Examples
-~~~~~~~~
+Examples:
 
+   - Not a QMP code block
+   - Merely a preformatted code block literal
+   It isn't even an rST list.
    - *verbatim*
    - {braces}
 
@@ -261,13 +260,11 @@ Features
 "cmd-feat2"
    another feature
 
+Example::
 
-Example
-~~~~~~~
+   -> "this example"
 
-   -> in
-
-   <- out
+   <- "has no title"
 
 
 "EVT_BOXED" (Event)
-- 
2.45.0