Hmm, trying to run a boot project with clojure 1.9.0 there's a conflict.

Classpath conflict: org.clojure/clojure version 1.8.0 already loaded, NOT loading version 1.9.0
java.lang.RuntimeException: Unable to resolve var: *print-namespace-maps* in this context
clojure.lang.ExceptionInfo: Unable to resolve var: *print-namespace-maps* in this context

boot.properties has already been defined with:

BOOT_CLOJURE_VERSION=1.9.0
BOOT_VERSION=2.8.1
BOOT_EMIT_TARGET=no

Running boot --version returns

BOOT_CLOJURE_NAME=org.clojure/clojure
BOOT_CLOJURE_VERSION=1.8.0
BOOT_VERSION=2.8.2

I've already tried to upgrade boot with boot -u, but the boot clojure version remains the same

Okay, found the error, there was a stray BOOT_CLOJURE_VERSION env setting that was causing the error