Introduce feature flag to switch between mimalloc major versions

Author: gschulze

.gitmodules

@@ -1,3 +1,6 @@
-[submodule "libmimalloc-sys/c_src/mimalloc"]
-	path = libmimalloc-sys/c_src/mimalloc
+[submodule "libmimalloc-sys/c_src/mimalloc/v2"]
+	path = libmimalloc-sys/c_src/mimalloc/v2
+	url = https://github.com/microsoft/mimalloc
+[submodule "libmimalloc-sys/c_src/mimalloc/v3"]
+	path = libmimalloc-sys/c_src/mimalloc/v3
 	url = https://github.com/microsoft/mimalloc

Cargo.toml

@@ -32,3 +32,4 @@ debug_in_debug = ["libmimalloc-sys/debug_in_debug"]
 local_dynamic_tls = ["libmimalloc-sys/local_dynamic_tls"]
 no_thp = ["libmimalloc-sys/no_thp"]
 extended = ["libmimalloc-sys/extended"]
+v3 = ["libmimalloc-sys/v3"]

libmimalloc-sys/Cargo.toml

@@ -34,6 +34,7 @@ extended = ["cty"]
 arena = []
 local_dynamic_tls = []
 no_thp = []
+v3 = []
 
 # Show `extended` on docs.rs since it's the full API surface.
 [package.metadata.docs.rs]

libmimalloc-sys/build.rs

@@ -3,9 +3,15 @@ use std::env;
 fn main() {
     let mut build = cc::Build::new();
 
-    build.include("c_src/mimalloc/include");
-    build.include("c_src/mimalloc/src");
-    build.file("c_src/mimalloc/src/static.c");
+    let version = if env::var("CARGO_FEATURE_V3").is_ok() {
+        "v3"
+    } else {
+        "v2"
+    };
+
+    build.include(format!("c_src/mimalloc/{version}/include"));
+    build.include(format!("c_src/mimalloc/{version}/src"));
+    build.file(format!("c_src/mimalloc/{version}/src/static.c"));
 
     let target_os = env::var("CARGO_CFG_TARGET_OS").expect("target_os not defined!");
     let target_family = env::var("CARGO_CFG_TARGET_FAMILY").expect("target_family not defined!");

libmimalloc-sys/c_src/mimalloc

@@ -1,9 +1,17 @@
+use std::env;
+
 fn main() {
+    let cargo_manifest_dir = env!("CARGO_MANIFEST_DIR");
+    let version = if env::var("CARGO_FEATURE_V3").is_ok() {
+        "v3"
+    } else {
+        "v2"
+    };
+
     let mut cfg = ctest2::TestGenerator::new();
     cfg.header("mimalloc.h")
-        .include(concat!(
-            env!("CARGO_MANIFEST_DIR"),
-            "/../c_src/mimalloc/include"
+        .include(format!(
+            "{cargo_manifest_dir}/../c_src/mimalloc/{version}/include"
         ))
         .cfg("feature", Some("extended"))
         .fn_cname(|rust, link_name| link_name.unwrap_or(rust).to_string())