diff --git a/Makefile b/Makefile
--- a/Makefile
+++ b/Makefile
@@ -133,7 +133,7 @@
 rust-tests:
 	cd $(HGROOT)/rust/hg-cpython \
 		&& $(CARGO) test --quiet --all \
-			--no-default-features --features "$(py_feature)"
+			--no-default-features --features "$(py_feature) $(HG_RUST_FEATURES)"
 
 check-code:
 	hg manifest | xargs python contrib/check-code.py
diff --git a/contrib/heptapod-ci.yml b/contrib/heptapod-ci.yml
--- a/contrib/heptapod-ci.yml
+++ b/contrib/heptapod-ci.yml
@@ -41,6 +41,12 @@
     variables:
         PYTHON: python3
 
+rust-cargo-test-py3-dirstate-tree:
+    <<: *rust_cargo_test
+    variables:
+        PYTHON: python3
+        HG_RUST_FEATURES: dirstate-tree
+
 test-py2:
     <<: *runtests
     variables:
@@ -82,6 +88,15 @@
         PYTHON: python3
         TEST_HGMODULEPOLICY: "rust+c"
 
+test-py3-rust-dirstate-tree:
+    <<: *runtests
+    variables:
+        HGWITHRUSTEXT: cpython
+        RUNTEST_ARGS: "--rust --blacklist /tmp/check-tests.txt"
+        PYTHON: python3
+        TEST_HGMODULEPOLICY: "rust+c"
+        HG_RUST_FEATURES: "dirstate-tree"
+
 test-py2-chg:
     <<: *runtests
     variables:
diff --git a/rust/README.rst b/rust/README.rst
--- a/rust/README.rst
+++ b/rust/README.rst
@@ -34,6 +34,15 @@
 One day we may use this environment variable to switch to new experimental
 binding crates like a hypothetical ``HGWITHRUSTEXT=hpy``.
 
+Special features
+================
+
+You might want to check the `features` section in ``hg-cpython/Cargo.toml``.
+It may contain features that might be interesting to try out.
+
+To use features from the Makefile, use the `HG_RUST_FEATURES` environment 
+variable: for instance `HG_RUST_FEATURES="some-feature other-feature"`
+
 Profiling
 =========
 
diff --git a/rust/hg-core/Cargo.toml b/rust/hg-core/Cargo.toml
--- a/rust/hg-core/Cargo.toml
+++ b/rust/hg-core/Cargo.toml
@@ -40,3 +40,9 @@
 clap = "*"
 pretty_assertions = "0.6.1"
 tempfile = "3.1.0"
+
+[features]
+# Use a (still unoptimized) tree for the dirstate instead of the current flat
+# dirstate. This is not yet recommended for performance reasons. A future
+# version might make it the default, or make it a runtime option.
+dirstate-tree = []
diff --git a/rust/hg-core/src/dirstate.rs b/rust/hg-core/src/dirstate.rs
--- a/rust/hg-core/src/dirstate.rs
+++ b/rust/hg-core/src/dirstate.rs
@@ -11,6 +11,7 @@
 
 pub mod dirs_multiset;
 pub mod dirstate_map;
+#[cfg(feature = "dirstate-tree")]
 pub mod dirstate_tree;
 pub mod parsers;
 pub mod status;
diff --git a/rust/hg-cpython/Cargo.toml b/rust/hg-cpython/Cargo.toml
--- a/rust/hg-cpython/Cargo.toml
+++ b/rust/hg-cpython/Cargo.toml
@@ -10,6 +10,7 @@
 
 [features]
 default = ["python27"]
+dirstate-tree = ["hg-core/dirstate-tree"]
 
 # Features to build an extension module:
 python27 = ["cpython/python27-sys", "cpython/extension-module-2-7"]