From a681d354e717a549595e9b687567dc7d05eaf29d Mon Sep 17 00:00:00 2001
From: Robert Hensing <robert@roberthensing.nl>
Date: Fri, 12 Jul 2024 23:02:08 +0200
Subject: [PATCH] Add fresh concatStringsSep without bug

The buggy version was previously renamed to
dropEmptyInitThenConcatStringsSep
---
 src/libutil/meson.build       |  3 ++
 src/libutil/strings-inline.hh | 31 +++++++++++++
 src/libutil/strings.cc        | 12 +++++
 src/libutil/strings.hh        | 21 +++++++++
 tests/unit/libutil/strings.cc | 83 +++++++++++++++++++++++++++++++++++
 5 files changed, 150 insertions(+)
 create mode 100644 src/libutil/strings-inline.hh
 create mode 100644 src/libutil/strings.cc
 create mode 100644 src/libutil/strings.hh
 create mode 100644 tests/unit/libutil/strings.cc

diff --git a/src/libutil/meson.build b/src/libutil/meson.build
index ac2b83536..fbfcbe67c 100644
--- a/src/libutil/meson.build
+++ b/src/libutil/meson.build
@@ -148,6 +148,7 @@ sources = files(
   'signature/signer.cc',
   'source-accessor.cc',
   'source-path.cc',
+  'strings.cc',
   'suggestions.cc',
   'tarfile.cc',
   'terminal.cc',
@@ -215,6 +216,8 @@ headers = [config_h] + files(
   'source-accessor.hh',
   'source-path.hh',
   'split.hh',
+  'strings.hh',
+  'strings-inline.hh',
   'suggestions.hh',
   'sync.hh',
   'tarfile.hh',
diff --git a/src/libutil/strings-inline.hh b/src/libutil/strings-inline.hh
new file mode 100644
index 000000000..10c1b19e6
--- /dev/null
+++ b/src/libutil/strings-inline.hh
@@ -0,0 +1,31 @@
+#pragma once
+
+#include "strings.hh"
+
+namespace nix {
+
+template<class C>
+std::string concatStringsSep(const std::string_view sep, const C & ss)
+{
+    size_t size = 0;
+    bool tail = false;
+    // need a cast to string_view since this is also called with Symbols
+    for (const auto & s : ss) {
+        if (tail)
+            size += sep.size();
+        size += std::string_view(s).size();
+        tail = true;
+    }
+    std::string s;
+    s.reserve(size);
+    tail = false;
+    for (auto & i : ss) {
+        if (tail)
+            s += sep;
+        s += i;
+        tail = true;
+    }
+    return s;
+}
+
+} // namespace nix
diff --git a/src/libutil/strings.cc b/src/libutil/strings.cc
new file mode 100644
index 000000000..15937d415
--- /dev/null
+++ b/src/libutil/strings.cc
@@ -0,0 +1,12 @@
+#include <string>
+
+#include "strings-inline.hh"
+#include "util.hh"
+
+namespace nix {
+
+template std::string concatStringsSep(std::string_view, const Strings &);
+template std::string concatStringsSep(std::string_view, const StringSet &);
+template std::string concatStringsSep(std::string_view, const std::vector<std::string> &);
+
+} // namespace nix
diff --git a/src/libutil/strings.hh b/src/libutil/strings.hh
new file mode 100644
index 000000000..3b112c409
--- /dev/null
+++ b/src/libutil/strings.hh
@@ -0,0 +1,21 @@
+#pragma once
+
+#include <list>
+#include <set>
+#include <string_view>
+#include <string>
+#include <vector>
+
+namespace nix {
+
+/**
+ * Concatenate the given strings with a separator between the elements.
+ */
+template<class C>
+std::string concatStringsSep(const std::string_view sep, const C & ss);
+
+extern template std::string concatStringsSep(std::string_view, const std::list<std::string> &);
+extern template std::string concatStringsSep(std::string_view, const std::set<std::string> &);
+extern template std::string concatStringsSep(std::string_view, const std::vector<std::string> &);
+
+}
diff --git a/tests/unit/libutil/strings.cc b/tests/unit/libutil/strings.cc
new file mode 100644
index 000000000..47a20770e
--- /dev/null
+++ b/tests/unit/libutil/strings.cc
@@ -0,0 +1,83 @@
+#include <gtest/gtest.h>
+
+#include "strings.hh"
+
+namespace nix {
+
+using Strings = std::vector<std::string>;
+
+/* ----------------------------------------------------------------------------
+ * concatStringsSep
+ * --------------------------------------------------------------------------*/
+
+TEST(concatStringsSep, empty)
+{
+    Strings strings;
+
+    ASSERT_EQ(concatStringsSep(",", strings), "");
+}
+
+TEST(concatStringsSep, justOne)
+{
+    Strings strings;
+    strings.push_back("this");
+
+    ASSERT_EQ(concatStringsSep(",", strings), "this");
+}
+
+TEST(concatStringsSep, emptyString)
+{
+    Strings strings;
+    strings.push_back("");
+
+    ASSERT_EQ(concatStringsSep(",", strings), "");
+}
+
+TEST(concatStringsSep, emptyStrings)
+{
+    Strings strings;
+    strings.push_back("");
+    strings.push_back("");
+
+    ASSERT_EQ(concatStringsSep(",", strings), ",");
+}
+
+TEST(concatStringsSep, threeEmptyStrings)
+{
+    Strings strings;
+    strings.push_back("");
+    strings.push_back("");
+    strings.push_back("");
+
+    ASSERT_EQ(concatStringsSep(",", strings), ",,");
+}
+
+TEST(concatStringsSep, buildCommaSeparatedString)
+{
+    Strings strings;
+    strings.push_back("this");
+    strings.push_back("is");
+    strings.push_back("great");
+
+    ASSERT_EQ(concatStringsSep(",", strings), "this,is,great");
+}
+
+TEST(concatStringsSep, buildStringWithEmptySeparator)
+{
+    Strings strings;
+    strings.push_back("this");
+    strings.push_back("is");
+    strings.push_back("great");
+
+    ASSERT_EQ(concatStringsSep("", strings), "thisisgreat");
+}
+
+TEST(concatStringsSep, buildSingleString)
+{
+    Strings strings;
+    strings.push_back("this");
+
+    ASSERT_EQ(concatStringsSep(",", strings), "this");
+}
+
+} // namespace nix