deps.edn support — design notes

How Jolt loads pure-Clojure libraries from a deps.edn, and why it's built the way it is. For how to use it, see building-and-deps.md.

Scope, decided up front:

git + local deps only — no Maven/~/.m2 resolution.
pure clj/cljc — anything needing the JVM won't load or run; expected.
no classpath abstraction — require just needs to find a dep's namespaces; "the classpath" is an ordered list of source directories.
own resolver, own reader — deps.edn is read by jolt's own reader, and git fetch/cache is a thin shell-out to git; no external package manager.
deps-agnostic runtime core — resolution is a CLI front-end concern, not a runtime one. The runtime knows nothing about deps.edn; it only consumes a list of source roots. The CLI resolves a deps.edn into those roots before running.

How resolution works

jolt.deps (jolt-core/jolt/deps.clj) reads deps.edn (jolt's own reader parses the EDN), then walks :deps:

:git/url + :git/sha (+ optional :deps/root) → clone the sha into the git cache and contribute the checkout (or its :deps/root subdir);
:local/root → the path as-is;
:mvn/* → skipped with a warning;
anything else → ignored.

git resolution shells out to git through jolt.host/sh — git init + remote add + fetch + reset at the requested sha. Clones land in a global, sha-immutable cache ($JOLT_GITLIBS, else ~/.jolt/gitlibs) shared across projects, the tools.gitlibs ~/.gitlibs model.

Each resolved dependency contributes its own :paths (default ["src"]) as source roots; the walk is breadth-first so every top-level coordinate registers before any transitive one — a top-level pin always wins, matching tools.deps. The result is a de-duplicated, ordered list of directories.

Two tools.deps features are mirrored in reduced form. Aliases: :aliases entries supply :extra-paths/:extra-deps (accumulate across the aliases selected with -A:a:b) and :main-opts (last-wins, run with -M:alias). Tasks: the honest subset of babashka's — a string task is a shell command, a map task is {:main-opts […]}; bare Clojure expressions aren't a separate task form.

How the CLI ties it together

jolt.main (jolt-core/jolt/main.clj) is the CLI dispatch. Driven by cli.ss, it resolves the project (jolt.deps/resolve-project), prepends the resolved roots, and de-sugars the argv into a run:

run -m NS args → load NS, call its -main;
run FILE → load the file;
-M:alias → run the alias's :main-opts;
-A:alias → add the alias's paths/deps, then run the rest;
repl → a line REPL;
path → print the resolved roots;
build -m NS [-o OUT] [--opt|--dev] → AOT-compile the app into a standalone binary;
<task> → run a deps.edn :tasks entry.

The resolver lives in the overlay alongside the runtime, but the runtime's only dependency interface is the list of source roots it's handed.

Native libraries

A library that binds C declares the shared objects it needs under :jolt/native, so jolt.main loads them before the namespace is required and its foreign-fn bindings resolve. Each entry is a map — {:name "sqlite3" :darwin ["libsqlite3.0.dylib" …] :linux ["libsqlite3.so.0" …]} — with optional :optional true (absence is fine, a feature-gated dep) and :process true (use the running process's own symbols, e.g. libc sockets, no external file). A project inherits its dependencies' :jolt/native.

Standalone binaries

joltc build -m NS compiles the app and every library into one executable (the runtime + compiler are baked in). It loads the resolved :jolt/native libs at startup, so an FFI app — sockets, SQLite — runs with no jolt or Chez on the path.

Output goes under the project's target/, cargo-style: target/release/<project> by default and with --opt, target/debug/<project> with --dev (the <name>.build scratch dir sits beside it). -o PATH overrides — absolute as-is, relative against the project dir. Paths resolve against the project (JOLT_PWD), not the CLI's cwd, since bin/joltc runs from the jolt repo.

:jolt/build {:embed ["resources" …]} bakes those directories' files into the binary; io/resource serves them from the image with no files on disk. Resources not embedded resolve at runtime against JOLT_PWD (or the cwd), so the ship-the-binary-with-its-resources/-dir model also works. Files read through io/file (e.g. a config.edn a config library loads) stay external by design — edit them without rebuilding.

A standalone build needs Chez's kernel dev files (libkernel.a, scheme.h) and a C compiler; JOLT_CHEZ_CSV overrides the auto-detected csv<ver>/<machine> dir. --opt turns on the inference/flatten/scalar-replace passes; the default release mode is const-fold only.

release and --opt are closed-world: a call between the app's own functions binds to its target directly, skipping the var lookup and generic dispatch a runtime call pays. That assumes app vars are final — mark one ^:redef (or ^:dynamic) to keep it redefinable and indirect. --dev keeps everything indirect/open. Calls into clojure.core stay indirect in every mode.

Limitations

Pure clj/cljc only — JVM interop, host classes, and unimplemented clojure.core corners fail. Coverage is per-function: a namespace can load with most functions working and a few not.
Source only; compiled .class files in a git dep are ignored.
git :git/sha must be a full SHA (git fetch can't resolve a short one).

Conformance

The known-working libraries (see libraries.md) and the examples exercise real pure-cljc git libraries end to end — resolving them from git, loading their namespaces, and running sample calls. A library fails when it relies on something Jolt doesn't provide — JVM interop, or a regex feature like Unicode property classes (\p{…}).

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