Improve diagnostics in failed binop lookup by detecting previously

emitted errors and doing the right thing.

Author: lattner

lib/Sema/TypeCheckExpr.cpp

@@ -182,8 +182,12 @@ static InfixData getInfixData(TypeChecker &TC, DeclContext *DC, Expr *E) {
                                                         E->getLoc()))
       return op->getInfixData();
   }
-  
-  TC.diagnose(E->getLoc(), diag::unknown_binop);
+
+  // If E is already an ErrorExpr, then we've diagnosed it as invalid already,
+  // otherwise emit an error.
+  if (!isa<ErrorExpr>(E))
+    TC.diagnose(E->getLoc(), diag::unknown_binop);
+
   // Recover with an infinite-precedence left-associative operator.
   return InfixData((unsigned char)~0U, Associativity::Left,
                    /*assignment*/ false);

test/decl/operators.swift

@@ -174,10 +174,8 @@ func ??= <T>(inout result : T?, rhs : Int) {  // ok
 
 
 _ = n*-4       // expected-error {{use of unresolved operator '*-'}}
-// expected-error @-1 2 {{operator is not a known binary operator}}
 
 if n==-1 {}    // expected-error {{use of unresolved operator '==-'}}
-// expected-error @-1 {{operator is not a known binary operator}}
 
 prefix operator ☃⃠ {}
 prefix func☃⃠(a : Int) -> Int { return a }
@@ -187,9 +185,7 @@ postfix func☃⃠(a : Int) -> Int { return a }
 _ = n☃⃠ ☃⃠ n   // Ok.
 _ = n ☃⃠ ☃⃠n   // Ok.
 _ = n☃⃠☃⃠n     // expected-error {{use of unresolved operator '☃⃠☃⃠'}}
-// expected-error @-1 2 {{operator is not a known binary operator}}
 _ = n ☃⃠☃⃠ n   // expected-error {{use of unresolved operator '☃⃠☃⃠'}}
-// expected-error @-1 2 {{operator is not a known binary operator}}