[clang] [Clang] Fix a number of issues involving expansion statements (PR #217110)

[Ambrose Leeb via cfe-commits]

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@@ -2188,6 +2188,30 @@ class DeclContext {
     }
   }
 
+  /// Test whether we're directly inside a function or method, but ignoring
+  /// any intervening expansion statements.
+  bool isInsideFunctionOrMethod() const {
+    return getEnclosingNonExpansionStatementContext()->isFunctionOrMethod();
+  }
+
+  /// Cast this to a FunctionDecl if it is one, ignoring any intervening
+  /// expansion statements. Returns nullptr if this is not a function.
+  FunctionDecl *getAsFunctionDecl() {
+    return dyn_cast<FunctionDecl>(getEnclosingNonExpansionStatementContext());
+  }
+
+  const FunctionDecl *getAsFunctionDecl() const {
+    return dyn_cast<FunctionDecl>(getEnclosingNonExpansionStatementContext());
+  }
+
+  FunctionDecl *castAsFunctionDecl() {
+    return cast<FunctionDecl>(getEnclosingNonExpansionStatementContext());
+  }
+
+  const FunctionDecl *castAsFunctionDecl() const {
+    return cast<FunctionDecl>(getEnclosingNonExpansionStatementContext());
+  }
----------------
Sirraide wrote:

See it’s hard to come up w/ a good name for these imo: I considered `getEnclosingFuctionDecl()`, but the issue with that is that it doesn’t always do that (e.g. if we’re inside a local class, we wouldn’t want this to return the function containing the local class since this helper is used to determine whether we’re currently directly inside a function, which we’re not if we’re in a class). 

`getEnclosingContextAsFunctionDecl()` would also be somewhat incorrect since there may be multiple nested expansion statement context, in which case the immediately enclosing context would still be an expansion statement, not a function, but if you think this still clearer than `getAsFunctionDecl()` then I’d be fine w/ switching to this

https://github.com/llvm/llvm-project/pull/217110