[CodeCompletion] Swap the exact-match if one is a better case-sensitive match

Instead of just taking the first one, consider whether there is a better
result because of case-sensitivity.

rdar://problem/25994202

Author: benlangmuir

test/SourceKit/CodeComplete/complete_sort_order.swift

@@ -183,3 +183,24 @@ func test6() {
 // VOID_1_RAW-NEXT: key.context: source.codecompletion.context.thismodule,
 // VOID_1_RAW-NEXT: key.num_bytes_to_erase: 0,
 // VOID_1_RAW-NEXT: key.not_recommended: 1,
+
+
+
+// RUN: %complete-test -tok=CASE_0 %s | FileCheck %s -check-prefix=CASE_0
+func test7() {
+  struct CaseSensitiveCheck {
+    var member: Int = 0
+  }
+  let caseSensitiveCheck = CaseSensitiveCheck()
+  #^CASE_0,caseSensitiveCheck,CaseSensitiveCheck^#
+}
+// CASE_0: Results for filterText: caseSensitiveCheck [
+// CASE_0: caseSensitiveCheck
+// CASE_0: CaseSensitiveCheck
+// CASE_0: caseSensitiveCheck.
+// CASE_0: ]
+// CASE_0: Results for filterText: CaseSensitiveCheck [
+// CASE_0: caseSensitiveCheck
+// CASE_0: CaseSensitiveCheck
+// CASE_0: CaseSensitiveCheck(
+// CASE_0: ]

tools/SourceKit/lib/SwiftLang/CodeCompletionOrganizer.cpp

@@ -586,8 +586,17 @@ void CodeCompletionOrganizer::Impl::addCompletionsWithFilter(
     bool isExactMatch = match && completion->getName().equals_lower(filterText);
 
     if (isExactMatch) {
-      if (!exactMatch)
+      if (!exactMatch) { // first match
         exactMatch = completion;
+      } else if (completion->getName() != exactMatch->getName()) {
+        if (completion->getName() == filterText && // first case-sensitive match
+            exactMatch->getName() != filterText)
+          exactMatch = completion;
+        else if (pattern.scoreCandidate(completion->getName()) > // better match
+                 pattern.scoreCandidate(exactMatch->getName()))
+          exactMatch = completion;
+      }
+
       match = (options.addInnerResults || options.addInnerOperators)
                   ? options.includeExactMatch
                   : true;