Merge pull request #7918 from zimbatm/fix-empty-nix-store-env

treat empty NIX_STORE_DIR env vars as unset

src/libstore/build/local-derivation-goal.cc

@@ -2062,7 +2062,7 @@ void LocalDerivationGoal::runChild()
 
             /* The tmpDir in scope points at the temporary build directory for our derivation. Some packages try different mechanisms
                to find temporary directories, so we want to open up a broader place for them to dump their files, if needed. */
-            Path globalTmpDir = canonPath(getEnv("TMPDIR").value_or("/tmp"), true);
+            Path globalTmpDir = canonPath(getEnvNonEmpty("TMPDIR").value_or("/tmp"), true);
 
             /* They don't like trailing slashes on subpath directives */
             if (globalTmpDir.back() == '/') globalTmpDir.pop_back();

src/libstore/globals.cc

@@ -30,15 +30,15 @@ static GlobalConfig::Register rSettings(&settings);
 
 Settings::Settings()
     : nixPrefix(NIX_PREFIX)
-    , nixStore(canonPath(getEnv("NIX_STORE_DIR").value_or(getEnv("NIX_STORE").value_or(NIX_STORE_DIR))))
-    , nixDataDir(canonPath(getEnv("NIX_DATA_DIR").value_or(NIX_DATA_DIR)))
-    , nixLogDir(canonPath(getEnv("NIX_LOG_DIR").value_or(NIX_LOG_DIR)))
-    , nixStateDir(canonPath(getEnv("NIX_STATE_DIR").value_or(NIX_STATE_DIR)))
-    , nixConfDir(canonPath(getEnv("NIX_CONF_DIR").value_or(NIX_CONF_DIR)))
+    , nixStore(canonPath(getEnvNonEmpty("NIX_STORE_DIR").value_or(getEnvNonEmpty("NIX_STORE").value_or(NIX_STORE_DIR))))
+    , nixDataDir(canonPath(getEnvNonEmpty("NIX_DATA_DIR").value_or(NIX_DATA_DIR)))
+    , nixLogDir(canonPath(getEnvNonEmpty("NIX_LOG_DIR").value_or(NIX_LOG_DIR)))
+    , nixStateDir(canonPath(getEnvNonEmpty("NIX_STATE_DIR").value_or(NIX_STATE_DIR)))
+    , nixConfDir(canonPath(getEnvNonEmpty("NIX_CONF_DIR").value_or(NIX_CONF_DIR)))
     , nixUserConfFiles(getUserConfigFiles())
-    , nixBinDir(canonPath(getEnv("NIX_BIN_DIR").value_or(NIX_BIN_DIR)))
+    , nixBinDir(canonPath(getEnvNonEmpty("NIX_BIN_DIR").value_or(NIX_BIN_DIR)))
     , nixManDir(canonPath(NIX_MAN_DIR))
-    , nixDaemonSocketFile(canonPath(getEnv("NIX_DAEMON_SOCKET_PATH").value_or(nixStateDir + DEFAULT_SOCKET_PATH)))
+    , nixDaemonSocketFile(canonPath(getEnvNonEmpty("NIX_DAEMON_SOCKET_PATH").value_or(nixStateDir + DEFAULT_SOCKET_PATH)))
 {
     buildUsersGroup = getuid() == 0 ? "nixbld" : "";
     lockCPU = getEnv("NIX_AFFINITY_HACK") == "1";

src/libutil/util.cc

@@ -54,6 +54,11 @@ std::optional<std::string> getEnv(const std::string & key)
     return std::string(value);
 }
 
+std::optional<std::string> getEnvNonEmpty(const std::string & key) {
+    auto value = getEnv(key);
+    if (value == "") return {};
+    return value;
+}
 
 std::map<std::string, std::string> getEnv()
 {

src/libutil/util.hh

@@ -39,6 +39,10 @@ extern const std::string nativeSystem;
 /* Return an environment variable. */
 std::optional<std::string> getEnv(const std::string & key);
 
+/* Return a non empty environment variable. Returns nullopt if the env
+variable is set to "" */
+std::optional<std::string> getEnvNonEmpty(const std::string & key);
+
 /* Get the entire environment. */
 std::map<std::string, std::string> getEnv();