handle the case where 0 or >1 allocs are enabled

In particular this fixes `cargo build --all-features`.

src/alloc/default.rs

+//! Default allocator with no special features
+
+/// Always returns the empty string
+pub(crate) fn memory_stats() -> String { Default::default() }
+
+/// Always returns the empty string
+pub(crate) fn memory_usage() -> String { Default::default() }

src/alloc/hardened.rs

-#![cfg(all(not(target_env = "msvc"), feature = "hardened_malloc", target_os = "linux", not(feature = "jemalloc")))]
-
 #[global_allocator]
 static HMALLOC: hardened_malloc_rs::HardenedMalloc = hardened_malloc_rs::HardenedMalloc;
 

src/alloc/je.rs

-#![cfg(all(not(target_env = "msvc"), feature = "jemalloc", not(feature = "hardened_malloc")))]
-#![allow(dead_code)]
-
 use std::ffi::{c_char, c_void};
 
 use tikv_jemalloc_ctl as mallctl;
@@ -10,8 +7,6 @@
 #[global_allocator]
 static JEMALLOC: jemalloc::Jemalloc = jemalloc::Jemalloc;
 
-pub(crate) fn version() -> &'static str { mallctl::version::read().expect("version string") }
-
 pub(crate) fn memory_usage() -> String {
 	use mallctl::stats;
 	let allocated = stats::allocated::read().unwrap_or_default() as f64 / 1024.0 / 1024.0;

src/alloc/mod.rs

-pub(crate) mod hardened;
-pub(crate) mod je;
-
-#[cfg(all(not(target_env = "msvc"), feature = "hardened_malloc", target_os = "linux", not(feature = "jemalloc")))]
-pub(crate) fn memory_usage() -> String { hardened::memory_usage() }
+//! Integration with allocators
 
+// jemalloc
 #[cfg(all(not(target_env = "msvc"), feature = "jemalloc", not(feature = "hardened_malloc")))]
-pub(crate) fn memory_usage() -> String { je::memory_usage() }
-
-#[cfg(any(target_env = "msvc", all(not(feature = "jemalloc"), not(feature = "hardened_malloc"))))]
-pub(crate) fn memory_usage() -> String { String::default() }
+mod je;
+#[cfg(all(not(target_env = "msvc"), feature = "jemalloc", not(feature = "hardened_malloc")))]
+pub(crate) use je::{memory_stats, memory_usage};
 
+// hardened_malloc
 #[cfg(all(not(target_env = "msvc"), feature = "hardened_malloc", target_os = "linux", not(feature = "jemalloc")))]
-pub(crate) fn memory_stats() -> String { hardened::memory_stats() }
-
-#[cfg(all(not(target_env = "msvc"), feature = "jemalloc", not(feature = "hardened_malloc")))]
-pub(crate) fn memory_stats() -> String { je::memory_stats() }
+mod hardened;
+#[cfg(all(not(target_env = "msvc"), feature = "hardened_malloc", target_os = "linux", not(feature = "jemalloc")))]
+pub(crate) use hardened::{memory_stats, memory_usage};
 
-#[cfg(any(target_env = "msvc", all(not(feature = "jemalloc"), not(feature = "hardened_malloc"))))]
-pub(crate) fn memory_stats() -> String { String::default() }
+// default, enabled when none or multiple of the above are enabled
+#[cfg(any(
+	not(any(feature = "jemalloc", feature = "hardened_malloc")),
+	all(feature = "jemalloc", feature = "hardened_malloc"),
+))]
+mod default;
+#[cfg(any(
+	not(any(feature = "jemalloc", feature = "hardened_malloc")),
+	all(feature = "jemalloc", feature = "hardened_malloc"),
+))]
+pub(crate) use default::{memory_stats, memory_usage};

src/main.rs

@@ -49,7 +49,7 @@
 	error::{Error, Result},
 };
 
-mod alloc;
+pub(crate) mod alloc;
 mod api;
 mod config;
 mod database;