[QoI] Check before trying to emit fix-it to convert from array to dictionary

lib/Sema/CSDiag.cpp

@@ -7254,11 +7254,12 @@ bool FailureDiagnosis::visitArrayExpr(ArrayExpr *E) {
         }
       }
     }
-
+
+    auto numElements = E->getNumElements();
     if (!Conformance) {
       // If the contextual type conforms to ExpressibleByDictionaryLiteral and
       // this is an empty array, then they meant "[:]".
-      if (E->getNumElements() == 0 &&
+      if (numElements == 0 &&
           isDictionaryLiteralCompatible(contextualType, CS, E->getLoc())) {
         diagnose(E->getStartLoc(), diag::should_use_empty_dictionary_literal)
           .fixItInsert(E->getEndLoc(), ":");
@@ -7271,13 +7272,19 @@ bool FailureDiagnosis::visitArrayExpr(ArrayExpr *E) {
 
       // If the contextual type conforms to ExpressibleByDictionaryLiteral, then
       // they wrote "x = [1,2]" but probably meant "x = [1:2]".
-      if ((E->getElements().size() & 1) == 0 && !E->getElements().empty() &&
+      if ((numElements & 1) == 0 && numElements > 0 &&
           isDictionaryLiteralCompatible(contextualType, CS, E->getLoc())) {
         auto diag = diagnose(E->getStartLoc(), diag::meant_dictionary_lit);
 
-        // Change every other comma into a colon.
-        for (unsigned i = 0, e = E->getElements().size()/2; i != e; ++i)
-          diag.fixItReplace(E->getCommaLocs()[i*2], ":");
+        // Change every other comma into a colon, only if the number
+        // of commas present matches the number of elements, because
+        // otherwise it might a structural problem with the expression
+        // e.g. ["a""b": 1].
+        const auto commaLocs = E->getCommaLocs();
+        if (commaLocs.size() == numElements - 1) {
+          for (unsigned i = 0, e = numElements / 2; i != e; ++i)
+            diag.fixItReplace(commaLocs[i*2], ":");
+        }
       }
 
       return true;

test/Constraints/dictionary_literal.swift

@@ -97,3 +97,17 @@ func testDefaultExistentials() {
   let _ = ["a" : "hello", 17 : "string"]
   // expected-error@-1{{heterogeneous collection literal could only be inferred to 'Dictionary<AnyHashable, String>'}}
 }
+
+// SR-4952, rdar://problem/32330004 - Assertion failure during swift::ASTVisitor<::FailureDiagnosis,...>::visit
+func rdar32330004_1() -> [String: Any] {
+  return ["a""one": 1, "two": 2, "three": 3] // expected-note {{did you mean to use a dictionary literal instead?}}
+  // expected-error@-1 2 {{expected ',' separator}}
+  // expected-error@-2 {{expected expression in container literal}}
+  // expected-error@-3 {{contextual type '[String : Any]' cannot be used with array literal}}
+}
+
+func rdar32330004_2() -> [String: Any] {
+  return ["a", 0, "one", 1, "two", 2, "three", 3]
+  // expected-error@-1 {{contextual type '[String : Any]' cannot be used with array literal}}
+  // expected-note@-2 {{did you mean to use a dictionary literal instead?}} {{14-15=:}} {{24-25=:}} {{34-35=:}} {{46-47=:}}
+}