[PATCH 09/37] qapi/common.py: Add indent manager

[John Snow]

Code style tools really dislike the use of global keywords, because it
generally involves re-binding the name at runtime which can have strange
effects depending on when and how that global name is referenced in
other modules.

Make a little indent level manager instead.

Signed-off-by: John Snow <jsnow@redhat.com>
---
 scripts/qapi/common.py | 50 +++++++++++++++++++++++++++++-------------
 scripts/qapi/visit.py  |  7 +++---
 2 files changed, 38 insertions(+), 19 deletions(-)

diff --git a/scripts/qapi/common.py b/scripts/qapi/common.py
index 4fb265a8bf..87d87b95e5 100644
--- a/scripts/qapi/common.py
+++ b/scripts/qapi/common.py
@@ -93,33 +93,53 @@ def c_name(name, protect=True):
 pointer_suffix = ' *' + eatspace
 
 
-def genindent(count):
-    ret = ''
-    for _ in range(count):
-        ret += ' '
-    return ret
+class Indent:
+    """
+    Indent-level management.
 
+    :param initial: Initial value, default 0.
+    """
+    def __init__(self, initial: int = 0) -> None:
+        self._level = initial
 
-indent_level = 0
+    def __int__(self) -> int:
+        """Return the indent as an integer."""
+        return self._level
 
+    def __repr__(self) -> str:
+        return "{}({:d})".format(type(self).__name__, self._level)
 
-def push_indent(indent_amount=4):
-    global indent_level
-    indent_level += indent_amount
+    def __str__(self) -> str:
+        """Return the indent as a string."""
+        return ' ' * self._level
 
+    def __bool__(self) -> bool:
+        """True when there is a non-zero indent."""
+        return bool(self._level)
 
-def pop_indent(indent_amount=4):
-    global indent_level
-    indent_level -= indent_amount
+    def push(self, amount: int = 4) -> int:
+        """Push `amount` spaces onto the indent, default four."""
+        self._level += amount
+        return self._level
+
+    def pop(self, amount: int = 4) -> int:
+        """Pop `amount` spaces off of the indent, default four."""
+        if self._level < amount:
+            raise ArithmeticError(
+                "Can't pop {:d} spaces from {:s}".format(amount, repr(self)))
+        self._level -= amount
+        return self._level
+
+
+INDENT = Indent(0)
 
 
 # Generate @code with @kwds interpolated.
 # Obey indent_level, and strip eatspace.
 def cgen(code, **kwds):
     raw = code % kwds
-    if indent_level:
-        indent = genindent(indent_level)
-        raw, _ = re.subn(r'^(?!(#|$))', indent, raw, flags=re.MULTILINE)
+    if INDENT:
+        raw, _ = re.subn(r'^(?!(#|$))', str(INDENT), raw, flags=re.MULTILINE)
     return re.sub(re.escape(eatspace) + r' *', '', raw)
 
 
diff --git a/scripts/qapi/visit.py b/scripts/qapi/visit.py
index 31bf46e7f7..66ce3dc52e 100644
--- a/scripts/qapi/visit.py
+++ b/scripts/qapi/visit.py
@@ -19,8 +19,7 @@
     gen_endif,
     gen_if,
     mcgen,
-    pop_indent,
-    push_indent,
+    INDENT,
 )
 from .gen import QAPISchemaModularCVisitor, ifcontext
 from .schema import QAPISchemaObjectType
@@ -68,7 +67,7 @@ def gen_visit_object_members(name, base, members, variants):
     if (visit_optional(v, "%(name)s", &obj->has_%(c_name)s)) {
 ''',
                          name=memb.name, c_name=c_name(memb.name))
-            push_indent()
+            INDENT.push()
         ret += mcgen('''
     if (!visit_type_%(c_type)s(v, "%(name)s", &obj->%(c_name)s, errp)) {
         return false;
@@ -77,7 +76,7 @@ def gen_visit_object_members(name, base, members, variants):
                      c_type=memb.type.c_name(), name=memb.name,
                      c_name=c_name(memb.name))
         if memb.optional:
-            pop_indent()
+            INDENT.pop()
             ret += mcgen('''
     }
 ''')
-- 
2.26.2