Join two URL path segments without introducing double slashes.

This method is designed for joining route prefixes and paths in web frameworks. It handles the common cases of trailing/leading slashes to produce clean URLs.

Behavior:

• If parent is empty, returns child as-is
• If child is empty, returns parent as-is
• If both have slashes at the join point, one is removed
• If neither has a slash at the join point, one is added

Examples: URLPath.join("/api", "/users") # => "/api/users" URLPath.join("/api/", "/users") # => "/api/users" URLPath.join("/api", "users") # => "/api/users" URLPath.join("", "/users") # => "/users" URLPath.join("/api", "") # => "/api" URLPath.join("/api", "/") # => "/api/"

Note: This does not normalize multiple consecutive slashes within paths. For example, URLPath.join("/api//v1", "users") produces "/api//v1/users".

Join two URL path segments, collapsing every slash at the seam to exactly one.

Seven route extractors had this open-coded, byte for byte: the JVM DSL ones (http4k, JAX-RS, Micronaut, the shared lambda-DSL extractor), AdonisJS, Elysia, and the Scala Play analyzer.

It is deliberately NOT .join, and the two are not interchangeable — .join removes at most one slash and keeps a trailing one:

join("/api//", "/users") # => "/api//users" join_trimmed(...) # => "/api/users"

join("/api/", "") # => "/api/" join_trimmed("/api/", "") # => "/api"

Use this where a framework's prefix stack can contribute repeated or trailing slashes that must not survive into the emitted URL; use .join where the segments are already normalised and a trailing slash is meaningful.