The following situation:

build/dir/*.js: [build/out/*.js]
build/out/*.js: [src/\1.ts]

When attempting to build all build/dir/*.js artifacts, you'd specify the following command line flags:

$ build/dir/\*

which in turn finds all targets matching the above selector. Note that the exact string build/out/*.js is returned and looked up in the filesystem, producing an error, as the target build/out/*.js does not represent a file, but set of files, and hence needs to be transformed.