release/19.x: [ObjC] Name lookup in methods shouldn't allow shadowing types (#116683)

[AZero13]

Arguably as a bug, Clang has previously not mixed up Objective-C parameter names with types. This allows developers to write parameter names that should shadow type names, but don't. For instance:

@interface Foo
-(void)foo:(int)id bar:(id)name; // OK
@end

Commit 9778808 changed the way that parameters are parsed to bring it more in line with how C parameters are parsed, but it breaks the example above. Given an expectation that the change wouldn't introduce source breaks, this is not something we can go forward with.

9778808 did this so that late-parsed attributes could reference Objective-C parameters. This change buffers Objective-C parameter info until after all parameters are parsed and turns them into parameter declarations before realizing late-parsed attributes instead.

Radar-ID: 139996306
(cherry picked from commit 8bdf13b)

[llvmbot]

@llvm/pr-subscribers-clang

Author: Rose (AreaZR)

Changes

Arguably as a bug, Clang has previously not mixed up Objective-C parameter names with types. This allows developers to write parameter names that should shadow type names, but don't. For instance:

@<!-- -->interface Foo
-(void)foo:(int)id bar:(id)name; // OK
@<!-- -->end

Commit 9778808 changed the way that parameters are parsed to bring it more in line with how C parameters are parsed, but it breaks the example above. Given an expectation that the change wouldn't introduce source breaks, this is not something we can go forward with.

9778808 did this so that late-parsed attributes could reference Objective-C parameters. This change buffers Objective-C parameter info until after all parameters are parsed and turns them into parameter declarations before realizing late-parsed attributes instead.

Radar-ID: 139996306
(cherry picked from commit 8bdf13b)

---

Full diff: https://github.com/llvm/llvm-project/pull/116863.diff

2 Files Affected:

• (modified) clang/lib/Parse/ParseObjc.cpp (+11)
• (added) clang/test/SemaObjC/method-param-named-id.m (+7)

diff --git a/clang/lib/Parse/ParseObjc.cpp b/clang/lib/Parse/ParseObjc.cpp
index 6a2088a73c55b9..c0e2834bfb01a9 100644
--- a/clang/lib/Parse/ParseObjc.cpp
+++ b/clang/lib/Parse/ParseObjc.cpp
@@ -1554,6 +1554,17 @@ Decl *Parser::ParseObjCMethodDecl(SourceLocation mLoc,
                                                     nullptr));
   }
 
+  // Turn ArgInfos into parameters. This must happen after parsing all
+  // parameters for bug compatibility with previous versions of Clang. (For
+  // instance, if a method declares a parameter called "id", that parameter must
+  // not shadow the "id" type.)
+  SmallVector<ParmVarDecl *, 12> ObjCParamInfo;
+  for (auto &ArgInfo : ArgInfos) {
+    ParmVarDecl *Param = Actions.ObjC().ActOnMethodParmDeclaration(
+        getCurScope(), ArgInfo, ObjCParamInfo.size(), MethodDefinition);
+    ObjCParamInfo.push_back(Param);
+  }
+
   // FIXME: Add support for optional parameter list...
   // If attributes exist after the method, parse them.
   MaybeParseAttributes(PAKM_CXX11 | (getLangOpts().ObjC ? PAKM_GNU : 0),
diff --git a/clang/test/SemaObjC/method-param-named-id.m b/clang/test/SemaObjC/method-param-named-id.m
new file mode 100644
index 00000000000000..8269c31116c32d
--- /dev/null
+++ b/clang/test/SemaObjC/method-param-named-id.m
@@ -0,0 +1,7 @@
+// RUN: %clang_cc1 -fsyntax-only -verify -Wno-objc-root-class %s
+
+
+@interface Foo
+-(void)paramNamedID:(int)id usesIDType:(id)notShadowed;
+-(void)paramNamedID:(int)id, id notShadowed; // expected-warning{{use of C-style parameters in Objective-C method declarations is deprecated}}
+@end

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