[Clang importer] After stripping a prefix, lowercase initialisms as well.

Author: DougGregor

include/swift/Basic/StringExtras.h

@@ -241,6 +241,16 @@ namespace swift {
     /// unchanged.
     StringRef toLowercaseWord(StringRef string, StringScratchSpace &scratch);
 
+    /// Lowercase the first word within the given camelCase string.
+    ///
+    /// \param string The string to lowercase.
+    /// \param scratch Scratch buffer used to form the resulting string.
+    ///
+    /// \returns the string with the first word lowercased, including
+    /// initialisms.
+    StringRef toLowercaseInitialisms(StringRef string,
+                                     StringScratchSpace &scratch);
+
     /// Sentence-case the given camelCase string by turning the first
     /// letter into an uppercase letter.
     ///

lib/Basic/StringExtras.cpp

@@ -752,9 +752,8 @@ static bool isPluralSuffix(StringRef word) {
   return word == "s" || word == "es" || word == "ies";
 }
 
-/// A form of toLowercaseWord that also lowercases acronyms.
-static StringRef toLowercaseWordAndAcronym(StringRef string,
-                                           StringScratchSpace &scratch) {
+StringRef camel_case::toLowercaseInitialisms(StringRef string,
+                                             StringScratchSpace &scratch) {
   if (string.empty())
     return string;
 
@@ -765,7 +764,8 @@ static StringRef toLowercaseWordAndAcronym(StringRef string,
   // Lowercase until we hit the an uppercase letter followed by a
   // non-uppercase letter.
   llvm::SmallString<32> scratchStr;
-  for (unsigned i = 0, n = string.size(); i != n; ++i) {
+  scratchStr.push_back(clang::toLowercase(string[0]));
+  for (unsigned i = 1, n = string.size(); i != n; ++i) {
     // If the next character is not uppercase, stop.
     if (i < n - 1 && !clang::isUppercase(string[i+1])) {
       // If the next non-uppercase character was not a letter, we seem
@@ -802,14 +802,14 @@ bool swift::omitNeedlessWords(StringRef &baseName,
   /// Local function that lowercases all of the base names and
   /// argument names before returning.
   auto lowercaseAcronymsForReturn = [&] {
-    StringRef newBaseName = toLowercaseWordAndAcronym(baseName, scratch);
+    StringRef newBaseName = toLowercaseInitialisms(baseName, scratch);
     if (baseName.data() != newBaseName.data()) {
       baseName = newBaseName;
       anyChanges = true;
     }
 
     for (StringRef &argName : argNames) {
-      StringRef newArgName = toLowercaseWordAndAcronym(argName, scratch);
+      StringRef newArgName = toLowercaseInitialisms(argName, scratch);
       if (argName.data() != newArgName.data()) {
         argName = newArgName;
         anyChanges = true;

lib/ClangImporter/ClangImporter.cpp

@@ -2571,9 +2571,11 @@ auto ClangImporter::Implementation::importFullName(
         baseName = baseName.substr(prefixLen);
 
         // If the result is a value, lowercase it.
-        if (isa<clang::ValueDecl>(D) && shouldLowercaseValueName(baseName))
-          baseName = camel_case::toLowercaseWord(baseName,
-                                                 omitNeedlessWordsScratch);
+        if (isa<clang::ValueDecl>(D) && shouldLowercaseValueName(baseName)) {
+          baseName =
+            camel_case::toLowercaseInitialisms(baseName,
+                                               omitNeedlessWordsScratch);
+        }
       }
     }
   }

test/IDE/print_omit_needless_words.swift

@@ -172,6 +172,9 @@
 // Don't leave just a '_'.
 // CHECK-FOUNDATION: func NS_()
 
+// Lowercasing initialisms.
+// CHECK-FOUNDATION: let httpRequestKey: String
+
 // Lowercasing initialisms with plurals.
 // CHECK-FOUNDATION: var urlsInText: [URL] { get }
 

test/Inputs/clang-importer-sdk/usr/include/Foundation.h

@@ -996,6 +996,7 @@ extern void NS123(void);
 extern void NSYELLING(void);
 extern void NS_SCREAMING(void);
 extern void NS_(void);
+extern NSString *NSHTTPRequestKey;
 
 @interface NSString (URLExtraction)
 @property (nonnull,copy,readonly) NSArray<NSURL *> *URLsInText;