tools.build "No such var" / "Wrong number of args" in CI

A build.clj using tools.build referenced a var that is not defined in the required namespace, or called a build function with the wrong number of arguments. The compiler or runtime rejects the call before the build runs.

What this error means

A clojure -T:build run fails with "Syntax error compiling ... No such var: b/copy-dir" or "Execution error ... Wrong number of args (N) passed to ...".

clj

Syntax error compiling at (build.clj:18:3).
No such var: b/uber
Execution error (ArityException) Wrong number of args (1) passed to: clojure.tools.build.api/compile-clj

Common causes

A misspelled or wrong tools.build var

The alias points at clojure.tools.build.api, but the function name is wrong or belongs to a different version of the API.

A call with the wrong argument shape

tools.build functions take a single options map; passing positional args or the wrong keys raises an arity or key error.

How to fix it

Call the real function with an options map

Require the tools.build api with a stable alias.
Use the correct function name and pass a single options map.
Run clojure -T:build <fn> to confirm.

build.clj

(require '[clojure.tools.build.api :as b])
(b/compile-clj {:basis basis :class-dir class-dir :src-dirs ["src"]})
(b/uber {:class-dir class-dir :uber-file "target/app.jar" :basis basis})

Pin the tools.build version

Pin the git coordinate so the API surface your build.clj uses is stable across runs.

deps.edn

{:build {:deps {io.github.clojure/tools.build {:git/tag "v0.10.5" :git/sha "2a21b7a"}}
         :ns-default build}}

How to prevent it

Pin tools.build to a known version and match its API.
Pass a single options map to each build function.
Run the build task locally before relying on it in CI.