[clang] [Parser][ObjC] Add -Wobjc-prefix-length warning option. (PR #97597)

[Timm Baeder via cfe-commits]

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@@ -204,6 +204,89 @@ void Parser::CheckNestedObjCContexts(SourceLocation AtLoc)
     Diag(Decl->getBeginLoc(), diag::note_objc_container_start) << (int)ock;
 }
 
+/// An Objective-C public name (a class name or protocol name) is
+/// expected to have a prefix as all names are in a single global
+/// namespace.
+///
+/// If the `-Wobjc-prefix=<list>` option is active, it specifies a list
+/// of permitted prefixes; classes and protocols must start with a
+/// prefix from that list.  Note that in this case, we check that
+/// the name matches <prefix>(<upper-case><not-upper-case>?)?, so e.g.
+/// if you specify `-Wobjc-prefix=NS`, then `NSURL` would not be valid;
+/// you would want to specify `-Wobjc-prefix=NS,NSURL` in that case.
+///
+/// If the -Wobjc-prefix-length is set to N, the name must start
+/// with N+1 capital letters, which must be followed by a character
+/// that is not a capital letter.
+///
+/// For instance, for N set to 2, the following are valid:
+///
+///          NSString
+///          NSArray
+///
+///      but these are not:
+///
+///          MyString
+///          NSKString
+///          NSnotAString
+///
+/// We make a special exception for NSCF things when the prefix is set
+/// to length 2, because that's an unusual special case in the implementation
+/// of the Cocoa frameworks.
+///
+/// Names that start with underscores are exempt from this check, but
+/// are reserved for the system and should not be used by user code.
+bool Parser::isObjCPublicNamePrefixAllowed(StringRef name) {
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tbaederr wrote:

Newly introduced  parameters and variables should start with an uppercase letter.

https://github.com/llvm/llvm-project/pull/97597