Throw an exception if you try to use composite :provided profile.

This is as close to a fix as we're likely to get for #2687

doc/PROFILES.md

@@ -230,6 +230,12 @@ This can be used to avoid duplication:
 It is not recommended to make a composite profile which contains both
 keywords and maps; they should either be all keywords or all maps.
 
+Composite profiles also cannot have certain types of metadata
+propagated, which makes them incompatible with the `:provided`
+profile. If you get the error "Composite profiles are incompatible with :provided."
+consider adding `^{:pom-scope :provided}` metadata to the profile map
+which contains the dependencies instead.
+
 ## Dynamic Eval
 
 Often you want to read an environment variable or execute a function to capture

leiningen-core/src/leiningen/core/project.clj

@@ -633,6 +633,9 @@
                                   :production :system :repl}
                                 profile))
             (warn "Warning: profile" profile "not found."))
+          (when (and (= :provided profile) (composite-profile? result))
+            (throw (Exception.
+                    "Composite profiles are incompatible with :provided.")))
           (lookup-profile* profiles result))
 
         (composite-profile? profile)