qapi/common.py: Convert comments into docstrings, and elaborate

As docstrings, they'll show up in documentation and IDE help.

The docstring style being targeted is the Sphinx documentation
style. Sphinx uses an extension of ReST with "domains". We use the
(implicit) Python domain, which supports a number of custom "info
fields". Those info fields are documented here:
https://www.sphinx-doc.org/en/master/usage/restructuredtext/domains.html#info-field-lists

Primarily, we use `:param X: descr`, `:return[s]: descr`, and `:raise[s]
Z: when`. Everything else is the Sphinx dialect of ReST.

(No, nothing checks or enforces this style that I am aware of. Sphinx
either chokes or succeeds, but does not enforce a standard of what is
otherwise inside the docstring. Pycharm does highlight when your param
fields are not aligned with the actual fields present. It does not
highlight missing return or exception statements. There is no existing
style guide I am aware of that covers a standard for a minimally
acceptable docstring. I am debating writing one.)

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
Reviewed-by: Cleber Rosa <crosa@redhat.com>
Message-Id: <20201009161558.107041-17-jsnow@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

scripts/qapi/common.py

@@ -15,15 +15,25 @@
 from typing import Optional, Sequence
 
 
+#: Magic string that gets removed along with all space to its right.
 EATSPACE = '\033EATSPACE.'
 POINTER_SUFFIX = ' *' + EATSPACE
 _C_NAME_TRANS = str.maketrans('.-', '__')
 
 
-# ENUMName -> ENUM_NAME, EnumName1 -> ENUM_NAME1
-# ENUM_NAME -> ENUM_NAME, ENUM_NAME1 -> ENUM_NAME1, ENUM_Name2 -> ENUM_NAME2
-# ENUM24_Name -> ENUM24_NAME
 def camel_to_upper(value: str) -> str:
+    """
+    Converts CamelCase to CAMEL_CASE.
+
+    Examples::
+
+        ENUMName -> ENUM_NAME
+        EnumName1 -> ENUM_NAME1
+        ENUM_NAME -> ENUM_NAME
+        ENUM_NAME1 -> ENUM_NAME1
+        ENUM_Name2 -> ENUM_NAME2
+        ENUM24_Name -> ENUM24_NAME
+    """
     c_fun_str = c_name(value, False)
     if value.isupper():
         return c_fun_str
@@ -45,21 +55,33 @@ def camel_to_upper(value: str) -> str:
 def c_enum_const(type_name: str,
                  const_name: str,
                  prefix: Optional[str] = None) -> str:
+    """
+    Generate a C enumeration constant name.
+
+    :param type_name: The name of the enumeration.
+    :param const_name: The name of this constant.
+    :param prefix: Optional, prefix that overrides the type_name.
+    """
     if prefix is not None:
         type_name = prefix
     return camel_to_upper(type_name) + '_' + c_name(const_name, False).upper()
 
 
-# Map @name to a valid C identifier.
-# If @protect, avoid returning certain ticklish identifiers (like
-# C keywords) by prepending 'q_'.
-#
-# Used for converting 'name' from a 'name':'type' qapi definition
-# into a generated struct member, as well as converting type names
-# into substrings of a generated C function name.
-# '__a.b_c' -> '__a_b_c', 'x-foo' -> 'x_foo'
-# protect=True: 'int' -> 'q_int'; protect=False: 'int' -> 'int'
 def c_name(name: str, protect: bool = True) -> str:
+    """
+    Map ``name`` to a valid C identifier.
+
+    Used for converting 'name' from a 'name':'type' qapi definition
+    into a generated struct member, as well as converting type names
+    into substrings of a generated C function name.
+
+    '__a.b_c' -> '__a_b_c', 'x-foo' -> 'x_foo'
+    protect=True: 'int' -> 'q_int'; protect=False: 'int' -> 'int'
+
+    :param name: The name to map.
+    :param protect: If true, avoid returning certain ticklish identifiers
+                    (like C keywords) by prepending ``q_``.
+    """
     # ANSI X3J11/88-090, 3.1.1
     c89_words = set(['auto', 'break', 'case', 'char', 'const', 'continue',
                      'default', 'do', 'double', 'else', 'enum', 'extern',
@@ -129,12 +151,16 @@ def decrease(self, amount: int = 4) -> None:
         self._level -= amount
 
 
+#: Global, current indent level for code generation.
 indent = Indentation()
 
 
-# Generate @code with @kwds interpolated.
-# Obey indent, and strip EATSPACE.
 def cgen(code: str, **kwds: object) -> str:
+    """
+    Generate ``code`` with ``kwds`` interpolated.
+
+    Obey `indent`, and strip `EATSPACE`.
+    """
     raw = code % kwds
     if indent:
         raw = re.sub(r'^(?!(#|$))', str(indent), raw, flags=re.MULTILINE)