fix: Adapt root prefix determination

libmamba/include/mamba/core/util_os.hpp

@@ -22,6 +22,7 @@ namespace mamba
 
     bool is_admin();
     fs::u8path get_self_exe_path();
+    fs::u8path get_libmamba_path();
 
     using PID =
 #ifdef _WIN32

libmamba/src/api/configuration.cpp

@@ -635,7 +635,7 @@ namespace mamba
             if (mamba_bin_path.empty())
             {
                 return make_unexpected(
-                    "`mamba` binary not found.\nPlease set `MAMBA_ROOT_PREFIX`.",
+                    "The root prefix of your installation cannot be found.\nPlease set `MAMBA_ROOT_PREFIX`.",
                     mamba_error_code::incorrect_usage
                 );
             }
@@ -653,9 +653,9 @@ namespace mamba
                 return make_unexpected("Empty root prefix.", mamba_error_code::incorrect_usage);
             }
 
-            if (!fs::exists(prefix / "pkgs")           //
-                && !fs::exists(prefix / "conda-meta")  //
-                && !fs::exists(prefix / "envs"))
+            // TODO: consider the conjunction (i.e. &&-chaining) of the following conditions.
+            auto qualifies_as_root_prefix = (fs::exists(prefix / "pkgs") || fs::exists(prefix / "conda-meta") || fs::exists(prefix / "envs"));
+            if (!qualifies_as_root_prefix)
             {
                 return make_unexpected(
                     fmt::format(
@@ -713,51 +713,79 @@ namespace mamba
             return { fs::weakly_canonical(std::move(prefix)) };
         }
 
-        auto get_default_root_prefix(fs::u8path& prefix) -> void
+        auto get_root_prefix() -> fs::u8path
         {
-            if (util::get_env("MAMBA_DEFAULT_ROOT_PREFIX"))
+            fs::u8path root_prefix = util::get_env("MAMBA_ROOT_PREFIX").value_or("");
+
+            if (!root_prefix.empty())
+            {
+                LOG_TRACE << "Using root prefix set in `MAMBA_ROOT_PREFIX`: " << root_prefix;
+                return root_prefix;
+            }
+
+            root_prefix = util::get_env("MAMBA_DEFAULT_ROOT_PREFIX").value_or("");
+
+            if (!root_prefix.empty())
             {
-                prefix = util::get_env("MAMBA_DEFAULT_ROOT_PREFIX").value();
                 LOG_WARNING << unindent(R"(
-                                    'MAMBA_DEFAULT_ROOT_PREFIX' is meant for testing purpose.
-                                    Consider using 'MAMBA_ROOT_PREFIX' instead)");
+                                'MAMBA_DEFAULT_ROOT_PREFIX' is meant for testing purpose.
+                                Consider using 'MAMBA_ROOT_PREFIX' instead)");
+                LOG_TRACE << "Using root prefix set in `MAMBA_DEFAULT_ROOT_PREFIX`: " << root_prefix;
+                return root_prefix;
             }
-            else
+
+            // Find the location of libmamba
+            const fs::u8path libmamba_path = get_libmamba_path();
+
+            // Find the environment directory of the executable
+            const fs::u8path env_prefix = fs::weakly_canonical(
+                libmamba_path.parent_path().parent_path()
+            );
+
+            if (auto maybe_prefix = validate_existing_root_prefix(env_prefix);
+                maybe_prefix.has_value())
             {
-#ifdef MAMBA_USE_INSTALL_PREFIX_AS_BASE
-                // mamba case
-                // set the root prefix as the mamba installation path
-                get_root_prefix_from_mamba_bin(util::which("mamba"))
-                    .transform([&](fs::u8path&& p) { prefix = std::move(p); })
-                    .or_else([](mamba_error&& error) { throw std::move(error); });
-#else
-                // micromamba case
-
-                // In 1.0, only micromamba was using this location.
-                const fs::u8path default_root_prefix_v1 = fs::u8path(util::user_home_dir())
-                                                          / "micromamba";
-
-                // In 2.0, we change the default location.
-                // We unconditionally name the subfolder "mamba" for compatibility between ``mamba``
-                // and ``micromamba``, as well as consistency with ``MAMBA_`` environment variables.
-                const fs::u8path default_root_prefix_v2 = fs::u8path(util::user_data_dir()) / "mamba";
-
-                validate_existing_root_prefix(default_root_prefix_v1)
-                    .or_else([&default_root_prefix_v2](const auto& /* error */)
-                             { return validate_root_prefix(default_root_prefix_v2); })
-                    .transform([&](fs::u8path&& p) { prefix = std::move(p); })
-                    .or_else([](mamba_error&& error) { throw std::move(error); });
-#endif
+                LOG_TRACE << "Using `libmamba`'s current environment as the root prefix: "
+                          << maybe_prefix.value();
+                return maybe_prefix.value();
             }
-        }
 
-        auto get_root_prefix() -> fs::u8path
-        {
-            fs::u8path root_prefix = util::get_env("MAMBA_ROOT_PREFIX").value_or("");
-            if (root_prefix.empty())
+            // From the environment directory, we might infer the root prefix.
+            const fs::u8path inferred_root_prefix = fs::weakly_canonical(
+                env_prefix.parent_path().parent_path()
+            );
+
+            if (auto maybe_prefix = validate_existing_root_prefix(env_prefix);
+                maybe_prefix.has_value())
             {
-                get_default_root_prefix(root_prefix);
+                LOG_TRACE << "Inferring and using the root prefix from `libmamba`'s current environment' as: "
+                          << maybe_prefix.value();
+                return maybe_prefix.value();
             }
+
+#ifdef MAMBA_USE_INSTALL_PREFIX_AS_BASE
+            // mamba case
+            // set the root prefix as the mamba installation path
+            get_root_prefix_from_mamba_bin(util::which("mamba"))
+                .transform([&](fs::u8path&& p) { root_prefix = std::move(p); })
+                .or_else([](mamba_error&& error) { throw std::move(error); });
+#else
+            // micromamba case
+            // In 1.0, only micromamba was using this location.
+            const fs::u8path default_root_prefix_v1 = fs::u8path(util::user_home_dir())
+                                                      / "micromamba";
+
+            // In 2.0, we change the default location.
+            // We unconditionally name the subfolder "mamba" for compatibility between ``mamba``
+            // and ``micromamba``, as well as consistency with ``MAMBA_`` environment variables.
+            const fs::u8path default_root_prefix_v2 = fs::u8path(util::user_data_dir()) / "mamba";
+
+            validate_existing_root_prefix(default_root_prefix_v1)
+                .or_else([&default_root_prefix_v2](const auto& /* error */)
+                         { return validate_root_prefix(default_root_prefix_v2); })
+                .transform([&](fs::u8path&& p) { root_prefix = std::move(p); })
+                .or_else([](mamba_error&& error) { throw std::move(error); });
+#endif
             return root_prefix;
         }
 

libmamba/src/core/util_os.cpp

@@ -3,7 +3,8 @@
 
 #ifndef _WIN32
 #include <clocale>
-
+// To find the path of `libmamba`'s library.
+#include <dlfcn.h>
 #include <sys/ioctl.h>
 #include <sys/utsname.h>
 #include <unistd.h>
@@ -32,6 +33,7 @@
 #include <fmt/ostream.h>
 #include <reproc++/run.hpp>
 
+#include "mamba/core/error_handling.hpp"
 #include "mamba/core/output.hpp"
 #include "mamba/core/util_os.hpp"
 #include "mamba/util/build.hpp"
@@ -89,6 +91,60 @@ namespace mamba
 #endif
     }
 
+    fs::u8path get_libmamba_path()
+    {
+#ifdef _WIN32
+        HMODULE hModule = NULL;
+        BOOL ret_code = GetModuleHandleExW(
+            GET_MODULE_HANDLE_EX_FLAG_FROM_ADDRESS | GET_MODULE_HANDLE_EX_FLAG_UNCHANGED_REFCOUNT,
+            (LPCWSTR) get_libmamba_path,
+            &hModule
+        );
+        if (!ret_code)
+        {
+            throw mamba::mamba_error(
+                "Could find libmamba's module handle. (GetModuleHandleExW failed)",
+                mamba_error_code::internal_failure
+            );
+        }
+        std::wstring buffer(MAX_PATH, '\0');
+        DWORD new_size = MAX_PATH;
+        DWORD size = 0;
+        while (true)
+        {
+            size = GetModuleFileNameW(hModule, buffer.data(), static_cast<DWORD>(buffer.size()));
+            if (size == 0)
+            {
+                throw mamba::mamba_error(
+                    "Could find the filename of the libmamba's module handle. (GetModuleFileNameW failed)",
+                    mamba_error_code::internal_failure
+                );
+            }
+            if (size < new_size)
+            {
+                break;
+            }
+
+            new_size *= 2;
+            buffer.resize(new_size);
+        }
+        buffer.resize(size);
+        return fs::absolute(buffer);
+#else
+        fs::u8path libmamba_path;
+        Dl_info dl_info;
+        if (!dladdr(reinterpret_cast<void*>(get_libmamba_path), &dl_info))
+        {
+            throw mamba_error(
+                "Could not find libmamba's path. (dladdr failed)",
+                mamba_error_code::internal_failure
+            );
+        }
+        libmamba_path = dl_info.dli_fname;
+        return libmamba_path;
+#endif
+    }
+
     bool is_admin()
     {
 #ifdef _WIN32

libmamba/src/download/downloader.cpp

@@ -86,8 +86,6 @@ namespace mamba::download
                 {
                     // Use the CA certificates from `conda-forge::ca-certificates` installed in the
                     // root prefix or the system CA certificates if the certificate is not present.
-                    fs::u8path libmamba_library_path;
-
                     fs::u8path root_prefix = detail::get_root_prefix();
                     fs::u8path env_prefix_conda_cert = root_prefix / "ssl" / "cacert.pem";
 

micromamba/etc/profile.d/mamba.sh.in

@@ -1,4 +1,10 @@
-export MAMBA_ROOT_PREFIX="@CMAKE_INSTALL_PREFIX@"
+if [ -z "${MAMBA_ROOT_PREFIX}" ]; then
+    echo "WARNING: MAMBA_ROOT_PREFIX is not set."
+    echo "WARNING: Please set `MAMBA_ROOT_PREFIX` to the root of your installation."
+    echo "WARNING: For now continuing with `MAMBA_ROOT_PREFIX` set to `@CMAKE_INSTALL_PREFIX@`."
+    export MAMBA_ROOT_PREFIX="@CMAKE_INSTALL_PREFIX@"
+fi
+
 __mamba_setup="$("@CMAKE_INSTALL_PREFIX@/@CMAKE_INSTALL_BINDIR@/mamba" shell hook --shell posix 2> /dev/null)"
 if [ $? -eq 0 ]; then
     eval "$__mamba_setup"