When determining the start of a declaration, ignore attributes that aren't at the start

Otherwise, we get bad attribute/modifier insertion locations for 'rethrows' functions

Author: DougGregor

include/swift/AST/DeclAttr.def

@@ -429,7 +429,7 @@ CONTEXTUAL_DECL_ATTR(weak, ReferenceOwnership,
   49)
 CONTEXTUAL_DECL_ATTR_ALIAS(unowned, ReferenceOwnership)
 SIMPLE_DECL_ATTR(rethrows, Rethrows,
-  OnFunc | OnConstructor | RejectByParser | ABIBreakingToAdd | ABIBreakingToRemove | APIBreakingToAdd | APIBreakingToRemove,
+  OnFunc | OnConstructor | DeclModifier | RejectByParser | ABIBreakingToAdd | ABIBreakingToRemove | APIBreakingToAdd | APIBreakingToRemove,
   57)
 CONTEXTUAL_SIMPLE_DECL_ATTR(indirect, Indirect,
   DeclModifier | OnEnum | OnEnumElement | ABIBreakingToAdd | ABIBreakingToRemove | APIStableToAdd | APIStableToRemove,

lib/AST/Attr.cpp

@@ -861,12 +861,26 @@ void DeclAttributes::print(ASTPrinter &Printer, const PrintOptions &Options,
     DA->print(Printer, Options, D);
 }
 
+static bool attributeIsNotAtStart(const DeclAttribute *attr) {
+  switch (attr->getKind()) {
+  case DeclAttrKind::Rethrows:
+  case DeclAttrKind::Reasync:
+    return true;
+
+  default:
+    return false;
+  }
+}
+
 SourceLoc DeclAttributes::getStartLoc(bool forModifiers) const {
   if (isEmpty())
     return SourceLoc();
 
   const DeclAttribute *lastAttr = nullptr;
   for (auto attr : *this) {
+    if (attributeIsNotAtStart(attr))
+      continue;
+
     if (attr->getRangeWithAt().Start.isValid() &&
         (!forModifiers || attr->isDeclModifier()))
       lastAttr = attr;

test/Unsafe/safe.swift

@@ -7,7 +7,7 @@
 func unsafeFunction() { }
 
 @unsafe
-struct UnsafeType { } // expected-note{{unsafe struct 'UnsafeType' declared here}}
+struct UnsafeType { } // expected-note 3{{unsafe struct 'UnsafeType' declared here}}
 
 @safe(unchecked)
 func f() {
@@ -25,6 +25,14 @@ func h(_: UnsafeType) { // expected-warning{{reference to unsafe struct 'UnsafeT
   unsafeFunction()
 }
 
+// expected-note@+1 {{make global function 'rethrowing' @unsafe to indicate that its use is not memory-safe}}{{1-1=@unsafe }}
+func rethrowing(body: (UnsafeType) throws -> Void) rethrows { } // expected-warning{{reference to unsafe struct 'UnsafeType' [Unsafe]}}
+
+class HasStatics {
+  // expected-note@+1{{make static method 'f' @unsafe to indicate that its use is not memory-safe}}{{3-3=@unsafe }}
+  static func f(_: UnsafeType) { } // expected-warning{{reference to unsafe struct 'UnsafeType' [Unsafe]}}
+}
+
 // Parsing issues
 @safe // expected-error{{expected '(' in 'safe' attribute}}
 func bad1() { }