fmt_vformat_mangle_name, fmt_vformat_mangle_format_string

Summary: So that we can use format-strings with named-args outside of the regime directly supported by `fmt::vformat`.

Reviewed By: Gownta

Differential Revision: D67320144

fbshipit-source-id: 3685d8115008d88b82deb82b774e274dea350022

folly/BUCK

@@ -568,9 +568,17 @@ cpp_library(
 
 cpp_library(
     name = "fmt_utility",
+    srcs = [
+        "FmtUtility.cpp",
+    ],
     headers = [
         "FmtUtility.h",
     ],
+    deps = [
+        ":range",
+        ":string",
+        "//folly/ssl:openssl_hash",
+    ],
     exported_deps = [
         "fbsource//third-party/fmt:fmt",
         ":cpp_attributes",

folly/FmtUtility.cpp

@@ -0,0 +1,60 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <folly/FmtUtility.h>
+
+#include <folly/Range.h>
+#include <folly/String.h>
+#include <folly/ssl/OpenSSLHash.h>
+
+namespace folly {
+
+std::string fmt_vformat_mangle_name_fn::operator()(
+    std::string_view const key) const {
+  auto& self = *this;
+  std::string out;
+  self(out, key);
+  return out;
+}
+
+void fmt_vformat_mangle_name_fn::operator()(
+    std::string& out, std::string_view const key) const {
+  auto const keyr = folly::ByteRange(folly::StringPiece(key));
+  uint8_t enc[32];
+  auto const encr = folly::MutableByteRange{std::begin(enc), std::end(enc)};
+#if FOLLY_OPENSSL_HAS_BLAKE2B
+  folly::ssl::OpenSSLHash::blake2s256(encr, keyr);
+#else
+  folly::ssl::OpenSSLHash::sha256(encr, keyr);
+#endif
+  out.push_back('_');
+  folly::hexlify(encr, out, true);
+}
+
+std::string fmt_vformat_mangle_format_string_fn::operator()(
+    std::string_view const str) const {
+  std::string out;
+  char const* pos = str.data();
+  format_string_for_each_named_arg(str, [&](auto const arg) {
+    out.append(pos, arg.data());
+    fmt_vformat_mangle_name(out, arg);
+    pos = arg.data() + arg.size();
+  });
+  out.append(pos, str.data() + str.size());
+  return out;
+}
+
+} // namespace folly

folly/FmtUtility.h

@@ -44,4 +44,27 @@ struct fmt_make_format_args_from_map_fn {
 inline constexpr fmt_make_format_args_from_map_fn
     fmt_make_format_args_from_map{};
 
+/// fmt_vformat_mangle_name_fn
+/// fmt_vformat_mangle_name
+///
+/// A helper function-object type and variable for mangling vformat named-arg
+/// names which fmt::vformat might not otherwise permit.
+struct fmt_vformat_mangle_name_fn {
+  std::string operator()(std::string_view const str) const;
+  void operator()(std::string& out, std::string_view const str) const;
+};
+inline constexpr fmt_vformat_mangle_name_fn fmt_vformat_mangle_name{};
+
+/// fmt_vformat_mangle_format_string_fn
+/// fmt_vformat_mangle_format_string
+///
+/// A helper function-object type and variable for mangling the content of
+/// vformat format-strings containing named-arg names which fmt::vformat might
+/// not otherwise permit.
+struct fmt_vformat_mangle_format_string_fn {
+  std::string operator()(std::string_view const str) const;
+};
+inline constexpr fmt_vformat_mangle_format_string_fn
+    fmt_vformat_mangle_format_string{};
+
 } // namespace folly

folly/String.h

@@ -783,7 +783,7 @@ struct format_string_for_each_named_arg_fn {
       }
       auto const arg = str.substr(beg, end - beg);
       auto const c = arg.empty() ? 0 : arg[0];
-      if (c == '_' || (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z')) {
+      if (c && !(c >= '0' && c <= '9')) {
         fn(arg);
       }
       str = str.substr(end);

folly/test/FmtUtilityTest.cpp

@@ -37,3 +37,16 @@ TEST_F(FmtUtilityTest, fmt_make_format_args_from_map_fn) {
                   {"adj"s, "silly"sv},
               })));
 }
+
+TEST_F(FmtUtilityTest, fmt_vformat_mangle) {
+  EXPECT_EQ(
+      "hello bob you silly goose",
+      fmt::vformat(
+          folly::fmt_vformat_mangle_format_string(
+              "hello {@pre-key|name} you {@pre-key|adj} goose"),
+          folly::fmt_make_format_args_from_map(
+              std::map<std::string, std::string_view>{
+                  {folly::fmt_vformat_mangle_name("@pre-key|name"), "bob"sv},
+                  {folly::fmt_vformat_mangle_name("@pre-key|adj"), "silly"sv},
+              })));
+}