Make inline declarations into a warning.

This fixes the regression at #1706 and will become an error with #1736.

Cython/Compiler/Parsing.py

@@ -2963,11 +2963,15 @@ def p_c_arg_decl(s, ctx, in_pyfunc, cmethod_flag = 0, nonempty = 0,
         annotation = p_test(s)
     if s.sy == '=':
         s.next()
-        if 'pxd' in ctx.level and 'inline' not in ctx.modifiers:
-            if s.sy not in ['*', '?']:
-                error(pos, "default values cannot be specified in pxd files, use ? or *")
-            default = ExprNodes.BoolNode(1)
+        if 'pxd' in ctx.level:
+            if s.sy in ['*', '?']:
+                # TODO(github/1736): Make this an error for inline declarations.
+                default = ExprNodes.NoneNode(pos)
                 s.next()
+            elif 'inline' in ctx.modifiers:
+                default = p_test(s)
+            else:
+                error(pos, "default values cannot be specified in pxd files, use ? or *")
         else:
             default = p_test(s)
     return Nodes.CArgDeclNode(pos,

Cython/Compiler/Symtab.py

@@ -1319,6 +1319,9 @@ class ModuleScope(Scope):
     def declare_cfunction(self, name, type, pos,
                           cname=None, visibility='private', api=0, in_pxd=0,
                           defining=0, modifiers=(), utility_code=None, overridable=False):
+        if not defining and 'inline' in modifiers:
+            # TODO(github/1736): Make this an error.
+            warning(pos, "Declarations should not be declared inline.", 1)
         # Add an entry for a C function.
         if not cname:
             if visibility == 'extern' or (visibility == 'public' and defining):