Add llvm::join_items to StringExtras.

llvm::join_items is similar to llvm::join, which produces a string
by concatenating a sequence of values together separated by a
given separator.  But it differs in that the arguments to
llvm::join() are same-type members of a container, whereas the
arguments to llvm::join_items are arbitrary types passed into
a variadic template.  The only requirement on parameters to
llvm::join_items (including for the separator themselves) is
that they be implicitly convertible to std::string or have
an overload of std::string::operator+

Differential Revision: https://reviews.llvm.org/D24880

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@282502 91177308-0d34-0410-b5e6-96231b3b80d8

Author: Zachary Turner

include/llvm/ADT/StringExtras.h

@@ -155,6 +155,8 @@ static inline StringRef getOrdinalSuffix(unsigned Val) {
 /// it if it is not printable or if it is an escape char.
 void PrintEscapedString(StringRef Name, raw_ostream &Out);
 
+namespace detail {
+
 template <typename IteratorT>
 inline std::string join_impl(IteratorT Begin, IteratorT End,
                              StringRef Separator, std::input_iterator_tag) {
@@ -189,12 +191,64 @@ inline std::string join_impl(IteratorT Begin, IteratorT End,
   return S;
 }
 
+template <typename Sep>
+inline void join_items_impl(std::string &Result, Sep Separator) {}
+
+template <typename Sep, typename Arg>
+inline void join_items_impl(std::string &Result, Sep Separator,
+                            const Arg &Item) {
+  Result += Item;
+}
+
+template <typename Sep, typename Arg1, typename... Args>
+inline void join_items_impl(std::string &Result, Sep Separator, const Arg1 &A1,
+                            Args &&... Items) {
+  Result += A1;
+  Result += Separator;
+  join_items_impl(Result, Separator, std::forward<Args>(Items)...);
+}
+
+inline size_t join_one_item_size(char C) { return 1; }
+inline size_t join_one_item_size(const char *S) { return S ? ::strlen(S) : 0; }
+
+template <typename T> inline size_t join_one_item_size(const T &Str) {
+  return Str.size();
+}
+
+inline size_t join_items_size() { return 0; }
+
+template <typename A1> inline size_t join_items_size(const A1 &A) {
+  return join_one_item_size(A);
+}
+template <typename A1, typename... Args>
+inline size_t join_items_size(const A1 &A, Args &&... Items) {
+  return join_one_item_size(A) + join_items_size(std::forward<Args>(Items)...);
+}
+}
+
 /// Joins the strings in the range [Begin, End), adding Separator between
 /// the elements.
 template <typename IteratorT>
 inline std::string join(IteratorT Begin, IteratorT End, StringRef Separator) {
   typedef typename std::iterator_traits<IteratorT>::iterator_category tag;
-  return join_impl(Begin, End, Separator, tag());
+  return detail::join_impl(Begin, End, Separator, tag());
+}
+
+/// Joins the strings in the parameter pack \p Items, adding \p Separator
+/// between the elements.  All arguments must be implicitly convertible to
+/// std::string, or there should be an overload of std::string::operator+=()
+/// that accepts the argument explicitly.
+template <typename Sep, typename... Args>
+inline std::string join_items(Sep Separator, Args &&... Items) {
+  std::string Result;
+  if (sizeof...(Items) == 0)
+    return Result;
+
+  size_t NS = detail::join_one_item_size(Separator);
+  size_t NI = detail::join_items_size(std::forward<Args>(Items)...);
+  Result.reserve(NI + (sizeof...(Items) - 1) * NS + 1);
+  detail::join_items_impl(Result, Separator, std::forward<Args>(Items)...);
+  return Result;
 }
 
 } // End llvm namespace

unittests/ADT/CMakeLists.txt

@@ -53,6 +53,7 @@ set(ADTSources
   SparseBitVectorTest.cpp
   SparseMultiSetTest.cpp
   SparseSetTest.cpp
+  StringExtrasTest.cpp
   StringMapTest.cpp
   StringRefTest.cpp
   TinyPtrVectorTest.cpp

unittests/ADT/StringExtrasTest.cpp

@@ -0,0 +1,52 @@
+//===- StringExtrasTest.cpp - Unit tests for String extras ----------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/StringExtras.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+
+TEST(StringExtrasTest, Join) {
+  std::vector<std::string> Items;
+  EXPECT_EQ("", join(Items.begin(), Items.end(), " <sep> "));
+
+  Items = {"foo"};
+  EXPECT_EQ("foo", join(Items.begin(), Items.end(), " <sep> "));
+
+  Items = {"foo", "bar"};
+  EXPECT_EQ("foo <sep> bar", join(Items.begin(), Items.end(), " <sep> "));
+
+  Items = {"foo", "bar", "baz"};
+  EXPECT_EQ("foo <sep> bar <sep> baz",
+            join(Items.begin(), Items.end(), " <sep> "));
+}
+
+TEST(StringExtrasTest, JoinItems) {
+  const char *Foo = "foo";
+  std::string Bar = "bar";
+  llvm::StringRef Baz = "baz";
+  char X = 'x';
+
+  EXPECT_EQ("", join_items(" <sep> "));
+  EXPECT_EQ("", join_items('/'));
+
+  EXPECT_EQ("foo", join_items(" <sep> ", Foo));
+  EXPECT_EQ("foo", join_items('/', Foo));
+
+  EXPECT_EQ("foo <sep> bar", join_items(" <sep> ", Foo, Bar));
+  EXPECT_EQ("foo/bar", join_items('/', Foo, Bar));
+
+  EXPECT_EQ("foo <sep> bar <sep> baz", join_items(" <sep> ", Foo, Bar, Baz));
+  EXPECT_EQ("foo/bar/baz", join_items('/', Foo, Bar, Baz));
+
+  EXPECT_EQ("foo <sep> bar <sep> baz <sep> x",
+            join_items(" <sep> ", Foo, Bar, Baz, X));
+
+  EXPECT_EQ("foo/bar/baz/x", join_items('/', Foo, Bar, Baz, X));
+}