Add a devenv dev shell via nix-gradle-wrapper

.gitignore

@@ -2,3 +2,4 @@
 build
 .kotlin
 .idea
+.devenv

devenv.lock

@@ -0,0 +1,82 @@
+{
+  "nodes": {
+    "devenv": {
+      "locked": {
+        "dir": "src/modules",
+        "lastModified": 1789991752,
+        "narHash": "sha256-SiH+H00IutELZBg7BBNo6r5DU6E+DG7DjrbeX5+QLa0=",
+        "owner": "cachix",
+        "repo": "devenv",
+        "rev": "1c57b5dea0d400af97053fdd1a536fca17378f73",
+        "type": "github"
+      },
+      "original": {
+        "dir": "src/modules",
+        "owner": "cachix",
+        "repo": "devenv",
+        "type": "github"
+      }
+    },
+    "nix-gradle-wrapper": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1790095744,
+        "narHash": "sha256-hzVOn9BrB1fbjQ32bbNIPal0yiTb6C46ZZaz4FsFgOU=",
+        "owner": "devinrsmith",
+        "repo": "nix-gradle-wrapper",
+        "rev": "bdaa336f22df5501834ab4e4d359a2c0dca63167",
+        "type": "github"
+      },
+      "original": {
+        "owner": "devinrsmith",
+        "repo": "nix-gradle-wrapper",
+        "type": "github"
+      }
+    },
+    "nixpkgs": {
+      "inputs": {
+        "nixpkgs-src": "nixpkgs-src"
+      },
+      "locked": {
+        "lastModified": 1789506231,
+        "narHash": "sha256-vNkJbtmqyBfFhn/HnzQo4ROuoyYWuy/allqTfJb4kMY=",
+        "owner": "cachix",
+        "repo": "devenv-nixpkgs",
+        "rev": "c2f38fe7f9e04d9aadd354d380f2bd40531d9737",
+        "type": "github"
+      },
+      "original": {
+        "owner": "cachix",
+        "ref": "rolling",
+        "repo": "devenv-nixpkgs",
+        "type": "github"
+      }
+    },
+    "nixpkgs-src": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1789370336,
+        "narHash": "sha256-6RSEDHIWQtesQKWSu5qRai8L2h4KgCgMEfJHstW99G4=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "c7def046b9a883d46974757852106483d741586f",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixpkgs-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "devenv": "devenv",
+        "nix-gradle-wrapper": "nix-gradle-wrapper",
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

devenv.nix

@@ -0,0 +1,57 @@
+{ pkgs, inputs, ... }:
+let
+  # seqlock/build.gradle.kts's multiRelease { targetVersions(8, 11) } (the
+  # me.champeau.mrjar plugin) needs both a Java 8 and a Java 11 toolchain --
+  # the base source set plus the java11 override/java11Test source sets.
+  # gradle-wrapper.nix's isolatedHomeHook disables Gradle's own toolchain
+  # auto-detect/auto-download, so all of these have to be registered
+  # explicitly via extraJdkHomes below rather than relying on scanning.
+  jdk8 = pkgs.jdk8;
+  jdk11 = pkgs.jdk11;
+
+  # One of the extra LTS runtimes build.gradle.kts's java17/21/25Test tasks
+  # exercise the java11 override classes against (see there) -- otherwise
+  # unrelated to running Gradle itself, unlike jdk25 below.
+  jdk17 = pkgs.jdk17;
+  jdk21 = pkgs.jdk21;
+
+  # Runs the Gradle 9 wrapper/daemon itself (Java Compatibility table:
+  # https://docs.gradle.org/current/userguide/compatibility.html -- Java 25
+  # supported for running Gradle since 9.1.0, we're on 9.7.1), independent of
+  # whatever JDK version(s) the project's own toolchains target. Also one of
+  # the extra LTS runtimes build.gradle.kts's java17/21/25Test tasks exercise
+  # the java11 override classes against.
+  jdk25 = pkgs.jdk25;
+
+  # On Linux a JDK package's .home is already the toolchain-detectable home;
+  # on Darwin, nixpkgs' JDK outputs are a symlink farm and the real home is
+  # nested at ${pkg.bundle}/Contents/Home (per nix-gradle-wrapper's own
+  # README -- passing the top-level .home there lists the same JDK twice).
+  jdkHome = pkg: if pkg ? bundle then "${pkg.bundle}/Contents/Home" else pkg.home;
+
+  gradleWrapper = import "${inputs.nix-gradle-wrapper}/gradle-wrapper.nix" {
+    inherit pkgs;
+    wrapperPropertiesFile = ./gradle/wrapper/gradle-wrapper.properties;
+    name = "seqlock";
+    # This is a tiny single-module library (no per-task -Xmx override in
+    # seqlock/build.gradle.kts), so the 4 GiB default per-worker assumption
+    # is a big overestimate -- it collapses org.gradle.workers.max to 1 on
+    # an 8 GiB machine. 512 MiB is generous for this project's tests/compile.
+    perWorkerMemBytes = 512 * 1024 * 1024;
+    extraJdkHomes = [ (jdkHome jdk8) (jdkHome jdk11) (jdkHome jdk17) (jdkHome jdk21) (jdkHome jdk25) ];
+    # Pins the daemon JVM explicitly (org.gradle.java.home) instead of
+    # relying on languages.java.jdk.package below having put jdk25 first on
+    # JAVA_HOME/PATH by the time ./gradlew starts the daemon.
+    javaHome = jdkHome jdk25;
+  };
+in
+{
+  languages.java.enable = true;
+  languages.java.jdk.package = jdk25;
+
+  packages = gradleWrapper.extraBuildInputs ++ [ jdk8 jdk11 jdk17 jdk21 ];
+
+  enterShell = gradleWrapper.isolatedHomeHook + gradleWrapper.warmupHook + ''
+    echo "seqlock dev shell ready"
+  '';
+}

devenv.yaml

@@ -0,0 +1,6 @@
+inputs:
+  nixpkgs:
+    url: github:cachix/devenv-nixpkgs/rolling
+  nix-gradle-wrapper:
+    url: github:devinrsmith/nix-gradle-wrapper
+    flake: false