[NFC] Add parsing helpers for @attr(<identifier>)

Extends the existing `parseSingleAttrOption()` helper to also be able to parse a single arbitrary `Identifier`. This simplifies the handling of `SwiftNativeObjCRuntimeBaseAttr`, `ObjCRuntimeNameAttr`, and `ProjectedValuePropertyAttr`.

Author: beccadax

include/swift/Parse/Parser.h

@@ -896,7 +896,7 @@ class Parser {
 
   /// Parse the specified expected token and return its location on success.  On failure, emit the specified
   /// error diagnostic,  a note at the specified note location, and return the location of the previous token.
-  bool parseMatchingToken(tok K, SourceLoc &TokLoc, Diag<> ErrorDiag,
+  bool parseMatchingToken(tok K, SourceLoc &TokLoc, Diagnostic ErrorDiag,
                           SourceLoc OtherLoc);
 
   /// Returns the proper location for a missing right brace, parenthesis, etc.

lib/Parse/ParseDecl.cpp

@@ -2061,7 +2061,7 @@ class LLVM_NODISCARD AttrOptionSwitch {
   bool isDeclModifier;
 
   // State:
-  StringRef exampleName;                  // empty: when() was never called
+  Diagnostic misparseDiagnostic = diag::invalid_diagnostic;
   Optional<R> result;                     // None: no when() has matched
 
 public:
@@ -2084,8 +2084,9 @@ class LLVM_NODISCARD AttrOptionSwitch {
   /// If the option has the identifier \p name, give it value \p value.
   AttrOptionSwitch<R, T> &when(StringLiteral name, T value) {
     // Save this to use in a future diagnostic, if needed.
-    if (exampleName.empty() && !name.empty())
-      exampleName = name;
+    if (misparseDiagnostic.is(diag::invalid_diagnostic) && !name.empty())
+      misparseDiagnostic = Diagnostic(diag::attr_expected_option_such_as,
+                                      attrName, name);
 
     // Does this string match?
     if (parsedName && *parsedName == name) {
@@ -2096,10 +2097,32 @@ class LLVM_NODISCARD AttrOptionSwitch {
     return *this;
   }
 
+  template<typename Body>
+  AttrOptionSwitch<R, T> &whenAny(Diagnostic misparse, Body body) {
+    if (misparseDiagnostic.is(diag::invalid_diagnostic))
+      misparseDiagnostic = misparse;
+
+    if (parsedName && !parsedName->empty()) {
+      assert(!result && "overlapping AttrOptionSwitch::whenAny()?");
+      result = std::move(body(*parsedName));
+    }
+
+    return *this;
+  }
+
+  template<typename Ret = AttrOptionSwitch<R, T>>
+  std::enable_if_t<std::is_same<T, Identifier>::value, Ret> &
+  whenAny(Diagnostic misparse) {
+    return whenAny(misparse, [&](StringRef parsed) {
+      return P.Context.getIdentifier(parsed);
+    });
+  }
+
   /// Diagnose if the option is missing or was not matched, returning either the
   /// option's value or \c None if an error was diagnosed.
   Optional<R> diagnoseWhenOmitted() {
-    assert(!exampleName.empty() && "No AttrOptionSwitch::when() calls");
+    assert(!misparseDiagnostic.is(diag::invalid_diagnostic)
+              && "No AttrOptionSwitch::when() calls");
 
     if (attrName.empty())
       // An error has already been diagnosed; nothing to do.
@@ -2108,8 +2131,7 @@ class LLVM_NODISCARD AttrOptionSwitch {
     if (!result) {
       if (!parsedName)
         // We parsed a non-identifier; diagnose it with `exampleName`.
-        P.diagnose(loc, diag::attr_expected_option_such_as, attrName,
-                   exampleName);
+        P.diagnose(loc, misparseDiagnostic);
       else if (*parsedName == "")
         // Option list was omitted; apparently this attr doesn't allow that.
         P.diagnose(loc, diag::attr_expected_lparen, attrName, isDeclModifier);
@@ -2601,29 +2623,15 @@ bool Parser::parseNewDeclAttribute(DeclAttributes &Attributes, SourceLoc AtLoc,
   }
 
   case DAK_SwiftNativeObjCRuntimeBase: {
-    if (!consumeIf(tok::l_paren)) {
-      diagnose(Loc, diag::attr_expected_lparen, AttrName,
-               DeclAttribute::isDeclModifier(DK));
-      return false;
-    }
-
-    if (Tok.isNot(tok::identifier)) {
-      diagnose(Loc, diag::swift_native_objc_runtime_base_must_be_identifier);
+    SourceRange range;
+    auto name = parseSingleAttrOption<Identifier>
+                      (*this, Loc, range, AttrName, DK)
+              .whenAny(diag::swift_native_objc_runtime_base_must_be_identifier)
+              .diagnoseWhenOmitted();
+    if (!name)
       return false;
-    }
-    
-    Identifier name;
-    consumeIdentifier(name, /*diagnoseDollarPrefix=*/false);
-
-    auto range = SourceRange(Loc, Tok.getRange().getStart());
 
-    if (!consumeIf(tok::r_paren)) {
-      diagnose(Loc, diag::attr_expected_rparen, AttrName,
-               DeclAttribute::isDeclModifier(DK));
-      return false;
-    }
-    
-    Attributes.add(new (Context) SwiftNativeObjCRuntimeBaseAttr(name,
+    Attributes.add(new (Context) SwiftNativeObjCRuntimeBaseAttr(*name,
                                             AtLoc, range, /*implicit*/ false));
     break;
   }
@@ -2864,30 +2872,15 @@ bool Parser::parseNewDeclAttribute(DeclAttributes &Attributes, SourceLoc AtLoc,
     break;
   }
   case DAK_ObjCRuntimeName: {
-    if (!consumeIf(tok::l_paren)) {
-      diagnose(Loc, diag::attr_expected_lparen, AttrName,
-               DeclAttribute::isDeclModifier(DK));
-      return false;
-    }
-
-    if (Tok.isNot(tok::identifier)) {
-      diagnose(Loc, diag::objc_runtime_name_must_be_identifier);
-      return false;
-    }
-
-    auto name = Tok.getText();
-
-    consumeToken(tok::identifier);
-
-    auto range = SourceRange(Loc, Tok.getRange().getStart());
-
-    if (!consumeIf(tok::r_paren)) {
-      diagnose(Loc, diag::attr_expected_rparen, AttrName,
-               DeclAttribute::isDeclModifier(DK));
+    SourceRange range;
+    auto name = parseSingleAttrOption<Identifier>
+                            (*this, Loc, range, AttrName, DK)
+                    .whenAny(diag::objc_runtime_name_must_be_identifier)
+                    .diagnoseWhenOmitted();
+    if (!name)
       return false;
-    }
 
-    Attributes.add(new (Context) ObjCRuntimeNameAttr(name, AtLoc, range,
+    Attributes.add(new (Context) ObjCRuntimeNameAttr(name->str(), AtLoc, range,
                                                      /*implicit*/ false));
     break;
   }
@@ -3032,30 +3025,16 @@ bool Parser::parseNewDeclAttribute(DeclAttributes &Attributes, SourceLoc AtLoc,
   }
 
   case DAK_ProjectedValueProperty: {
-    if (!consumeIf(tok::l_paren)) {
-      diagnose(Loc, diag::attr_expected_lparen, AttrName,
-               DeclAttribute::isDeclModifier(DK));
-      return false;
-    }
-
-    if (Tok.isNot(tok::identifier)) {
-      diagnose(Loc, diag::projection_value_property_not_identifier);
-      return false;
-    }
-
-    Identifier name;
-    consumeIdentifier(name, /*diagnoseDollarPrefix=*/false);
-
-    auto range = SourceRange(Loc, Tok.getRange().getStart());
-
-    if (!consumeIf(tok::r_paren)) {
-      diagnose(Loc, diag::attr_expected_rparen, AttrName,
-               DeclAttribute::isDeclModifier(DK));
+    SourceRange range;
+    auto name = parseSingleAttrOption<Identifier>
+                            (*this, Loc, range, AttrName, DK)
+                    .whenAny(diag::projection_value_property_not_identifier)
+                    .diagnoseWhenOmitted();
+    if (!name)
       return false;
-    }
 
     Attributes.add(new (Context) ProjectedValuePropertyAttr(
-        name, AtLoc, range, /*implicit*/ false));
+        *name, AtLoc, range, /*implicit*/ false));
     break;
   }
   case DAK_TypeSequence: {

lib/Parse/Parser.cpp

@@ -975,7 +975,7 @@ bool Parser::parseToken(tok K, SourceLoc &TokLoc, const Diagnostic &D) {
   return true;
 }
 
-bool Parser::parseMatchingToken(tok K, SourceLoc &TokLoc, Diag<> ErrorDiag,
+bool Parser::parseMatchingToken(tok K, SourceLoc &TokLoc, Diagnostic ErrorDiag,
                                 SourceLoc OtherLoc) {
   Diag<> OtherNote;
   switch (K) {