Make errnoStr return std::string instead of fbstring

Summary:
The result of `errnoStr` is often converted to `std::string` so returning `fbstring` adds an extra copy. Make it return `std::string` instead. This will also allow removing dependency between `String.h` and `FBString.h`.

(Note: this ignores all push blocking failures!)

Reviewed By: yfeldblum

Differential Revision: D20195395

fbshipit-source-id: 0dc65f1566911156be3fcb715dd105c58f2a8822

folly/String.cpp

@@ -472,7 +472,7 @@ std::string hexDump(const void* ptr, size_t size) {
 // selects proper function.
 
 FOLLY_MAYBE_UNUSED
-static fbstring invoke_strerror_r(
+static std::string invoke_strerror_r(
     int (*strerror_r)(int, char*, size_t),
     int err,
     char* buf,
@@ -482,7 +482,7 @@ static fbstring invoke_strerror_r(
 
   // OSX/FreeBSD use EINVAL and Linux uses -1 so just check for non-zero
   if (r != 0) {
-    return to<fbstring>(
+    return to<std::string>(
         "Unknown error ", err, " (strerror_r failed with error ", errno, ")");
   } else {
     return buf;
@@ -490,7 +490,7 @@ static fbstring invoke_strerror_r(
 }
 
 FOLLY_MAYBE_UNUSED
-static fbstring invoke_strerror_r(
+static std::string invoke_strerror_r(
     char* (*strerror_r)(int, char*, size_t),
     int err,
     char* buf,
@@ -499,7 +499,7 @@ static fbstring invoke_strerror_r(
   return strerror_r(err, buf, buflen);
 }
 
-fbstring errnoStr(int err) {
+std::string errnoStr(int err) {
   int savedErrno = errno;
 
   // Ensure that we reset errno upon exit.
@@ -508,7 +508,7 @@ fbstring errnoStr(int err) {
   char buf[1024];
   buf[0] = '\0';
 
-  fbstring result;
+  std::string result;
 
   // https://developer.apple.com/library/mac/documentation/Darwin/Reference/ManPages/man3/strerror_r.3.html
   // http://www.kernel.org/doc/man-pages/online/pages/man3/strerror.3.html
@@ -518,7 +518,7 @@ fbstring errnoStr(int err) {
   // with strerrorlen_s). Note strerror_r and _s have swapped args.
   int r = strerror_s(buf, sizeof(buf), err);
   if (r != 0) {
-    result = to<fbstring>(
+    result = to<std::string>(
         "Unknown error ", err, " (strerror_r failed with error ", errno, ")");
   } else {
     result.assign(buf);

folly/String.h

@@ -380,11 +380,11 @@ void hexDump(const void* ptr, size_t size, OutIt out);
 std::string hexDump(const void* ptr, size_t size);
 
 /**
- * Return a fbstring containing the description of the given errno value.
+ * Return a string containing the description of the given errno value.
  * Takes care not to overwrite the actual system errno, so calling
  * errnoStr(errno) is valid.
  */
-fbstring errnoStr(int err);
+std::string errnoStr(int err);
 
 /*
  * Split a string into a list of tokens by delimiter.

folly/experimental/test/NestedCommandLineAppExample.cpp

@@ -57,11 +57,11 @@ class Concatenator {
 
 // clang-format off
 [[noreturn]] void throwOutputError() {
-  throw OutputError(folly::errnoStr(errno).toStdString());
+  throw OutputError(folly::errnoStr(errno));
 }
 
 [[noreturn]] void throwInputError() {
-  throw InputError(folly::errnoStr(errno).toStdString());
+  throw InputError(folly::errnoStr(errno));
 }
 // clang-format on
 
@@ -146,13 +146,13 @@ void runEcho(
     const char* sep = "";
     for (auto& arg : args) {
       if (printf("%s%s", sep, arg.c_str()) < 0) {
-        throw OutputError(folly::errnoStr(errno).toStdString());
+        throw OutputError(folly::errnoStr(errno));
       }
       sep = " ";
     }
     if (!options["-n"].as<bool>()) {
       if (putchar('\n') == EOF) {
-        throw OutputError(folly::errnoStr(errno).toStdString());
+        throw OutputError(folly::errnoStr(errno));
       }
     }
   } catch (const OutputError& e) {