Start Tazelish with its command line and version files

Tazelish installs Tazel and chooses which version of it runs, for those
who use Tazel alone. This first part holds everything that needs no
download:

- Versions: MAJOR.SEMIMAJOR.MINOR.PATCH without leading zeros,
  unstable, nightly, and YYYY-MM-DD-unstable or -nightly with a date
  the calendar has.
- The command line, read by hand into a typed command: install, use
  and default with --force before or after the version, self
  update|remove|purge, and help with or without a command. A wrong
  command line ends with exit code 2.
- tazelish.txt and config.txt: the nearest tazelish.txt in the current
  folder or above it comes first, then $HOME/.tazelish/config.txt or
  %USERPROFILE%\.tazelish\config.txt. use and default refuse to write
  over a file that exists unless --force is given.

install and self download from static.tazel.net, which this build does
not do; they say so and end with exit code 1.

C++17 with fmt, tested with Catch3, built by Bazel (clang-cl on
Windows, with the rules_cc patch the Tala repository carries). The code
throws no exceptions and builds with warnings as errors; the tests
leave out -Wconversion, which the headers of Catch3 do not pass. CI
tests on Linux, macOS and Windows.

1 files changed, 125 insertions, 0 deletions

diff --git a/Tests/VersionFilesTest.cpp b/Tests/VersionFilesTest.cpp
new file mode 100644
index 0000000..c7d8cfe
--- /dev/null
+++ b/Tests/VersionFilesTest.cpp
@@ -0,0 +1,125 @@
+// SPDX-FileCopyrightText: 2026 Progmasoft <support@progmasoft.com>
+// SPDX-License-Identifier: MPL-2.0 WITH AdditionRef-Progmasoft-Exception-2.0
+
+#include <Progmasoft/Catch3.hpp>
+#include <cstdlib>
+#include <fstream>
+#include <string>
+
+#include "Progmasoft/Tazelish/VersionFiles.hpp"
+
+namespace fs = std::filesystem;
+namespace tazelish = Progmasoft::Tazelish;
+
+namespace
+{
+
+    // A folder of its own below the temporary folder of the test, emptied
+    // first.
+    fs::path
+    Scratch(const std::string &name)
+    {
+        const char *root = std::getenv("TEST_TMPDIR"); // NOLINT
+        const fs::path folder
+            = (root != nullptr ? fs::path(root) : fs::temp_directory_path())
+              / ("tazelish-" + name);
+        fs::remove_all(folder);
+        fs::create_directories(folder);
+        return folder;
+    }
+
+    void
+    WriteText(const fs::path &file, const std::string &text)
+    {
+        fs::create_directories(file.parent_path());
+        std::ofstream(file, std::ios::binary) << text;
+    }
+
+    tazelish::Version
+    Nightly()
+    {
+        return tazelish::Newest{ tazelish::Channel::kNightly };
+    }
+
+    std::string
+    Selected(const fs::path &directory, const fs::path &home)
+    {
+        const auto selected = tazelish::SelectVersion(directory, home);
+        REQUIRE(std::holds_alternative<tazelish::Selection>(selected));
+        return tazelish::FormatVersion(
+            std::get<tazelish::Selection>(selected).version);
+    }
+
+} // namespace
+
+TEST_CASE("The nearest tazelish.txt comes before config.txt", "[files]")
+{
+    const fs::path root = Scratch("nearest");
+    const fs::path home = root / "home";
+    const fs::path project = root / "project";
+    const fs::path nested = project / "Sources" / "Deep";
+    fs::create_directories(nested);
+
+    CHECK(std::holds_alternative<tazelish::NoSelection>(
+        tazelish::SelectVersion(nested, home)));
+
+    WriteText(tazelish::ConfigFile(home), "nightly\n");
+    auto selected = tazelish::SelectVersion(nested, home);
+    REQUIRE(std::holds_alternative<tazelish::Selection>(selected));
+    CHECK(std::get<tazelish::Selection>(selected).source
+          == tazelish::VersionSource::kUser);
+
+    WriteText(project / "tazelish.txt", "\xEF\xBB\xBF 0.4.0.3\r\n");
+    selected = tazelish::SelectVersion(nested, home);
+    REQUIRE(std::holds_alternative<tazelish::Selection>(selected));
+    const auto &selection = std::get<tazelish::Selection>(selected);
+    CHECK(selection.source == tazelish::VersionSource::kProject);
+    CHECK(selection.file == project / "tazelish.txt");
+    CHECK(Selected(nested, home) == "0.4.0.3");
+
+    WriteText(project / "Sources" / "tazelish.txt", "2026-11-05-unstable");
+    CHECK(Selected(nested, home) == "2026-11-05-unstable");
+}
+
+TEST_CASE("A file that names no version is an error", "[files]")
+{
+    const fs::path root = Scratch("invalid");
+    WriteText(root / "tazelish.txt", "latest\n");
+    auto selected = tazelish::SelectVersion(root, std::nullopt);
+    REQUIRE(std::holds_alternative<tazelish::FileError>(selected));
+    CHECK(std::get<tazelish::FileError>(selected).message.find("'latest'")
+          != std::string::npos);
+
+    WriteText(root / "tazelish.txt", std::string(200, '1'));
+    selected = tazelish::SelectVersion(root, std::nullopt);
+    REQUIRE(std::holds_alternative<tazelish::FileError>(selected));
+    CHECK(std::get<tazelish::FileError>(selected).message
+          == "holds more than a version");
+
+    fs::remove(root / "tazelish.txt");
+    fs::create_directory(root / "tazelish.txt");
+    CHECK(std::holds_alternative<tazelish::FileError>(
+        tazelish::ReadVersionFile(root / "tazelish.txt")));
+}
+
+TEST_CASE("Writing over a version file needs --force", "[files]")
+{
+    const fs::path root = Scratch("force");
+    const fs::path config = tazelish::ConfigFile(root / "home");
+
+    CHECK_FALSE(tazelish::WriteVersionFile(config, Nightly(), false));
+    auto read = tazelish::ReadVersionFile(config);
+    REQUIRE(std::holds_alternative<tazelish::Version>(read));
+    CHECK(std::get<tazelish::Version>(read) == Nightly());
+
+    const tazelish::Version release = tazelish::Release{ 0, 4, 0, 3 };
+    const auto refused = tazelish::WriteVersionFile(config, release, false);
+    REQUIRE(refused.has_value());
+    CHECK(refused->message.find("--force") != std::string::npos);
+    CHECK(std::get<tazelish::Version>(tazelish::ReadVersionFile(config))
+          == Nightly());
+
+    CHECK_FALSE(tazelish::WriteVersionFile(config, release, true));
+    CHECK(std::get<tazelish::Version>(tazelish::ReadVersionFile(config))
+          == release);
+}