Print error when HOME is not set (#7376)

In some configurations, such as when using the runit supervisor and its
tool chpst, the HOME variable might be unset. This resulted in an
unclear error message that was hard to pin down.

src/porting.cpp

@@ -351,6 +351,21 @@ bool getCurrentExecPath(char *buf, size_t len)
 #endif
 
 
+//// Non-Windows
+#if !defined(_WIN32)
+
+const char *getHomeOrFail()
+{
+	const char *home = getenv("HOME");
+	// In rare cases the HOME environment variable may be unset
+	FATAL_ERROR_IF(!home,
+		"Required environment variable HOME is not set");
+	return home;
+}
+
+#endif
+
+
 //// Windows
 #if defined(_WIN32)
 
@@ -430,7 +445,7 @@ bool setSystemPaths()
 	}
 
 #ifndef __ANDROID__
-	path_user = std::string(getenv("HOME")) + DIR_DELIM "."
+	path_user = std::string(getHomeOrFail()) + DIR_DELIM "."
 		+ PROJECT_NAME;
 #endif
 
@@ -454,7 +469,7 @@ bool setSystemPaths()
 	}
 	CFRelease(resources_url);
 
-	path_user = std::string(getenv("HOME"))
+	path_user = std::string(getHomeOrFail())
 		+ "/Library/Application Support/"
 		+ PROJECT_NAME;
 	return true;
@@ -466,7 +481,7 @@ bool setSystemPaths()
 bool setSystemPaths()
 {
 	path_share = STATIC_SHAREDIR;
-	path_user  = std::string(getenv("HOME")) + DIR_DELIM "."
+	path_user  = std::string(getHomeOrFail()) + DIR_DELIM "."
 		+ lowercase(PROJECT_NAME);
 	return true;
 }