Add filesystem func to transform a path to a URI

In a few places across Base and the stdlib, we emit paths that we like
people to be able to click on in their terminal and editor. Up to this
point, we have relied on auto-filepath detection, but this does not
allow for alternative link text, such as contracted paths.

Doing so (via OSC 8 terminal links for example) requires filepath URI
encoding.

This functionality was previously part of a PR modifying stacktrace
printing, but after that became held up for unrelated reasons and
another PR appeared that would benefit from this utility, I've split out
this functionality so it can be used before the stacktrace printing PR
is resolved.

base/path.jl

@@ -613,3 +613,23 @@ relpath(path::AbstractString, startpath::AbstractString) =
 for f in (:isdirpath, :splitdir, :splitdrive, :splitext, :normpath, :abspath)
     @eval $f(path::AbstractString) = $f(String(path))
 end
+
+"""
+    uripath(path::AbstractString)
+
+Encode `path` as a URI as per [RFC1738](https://www.rfc-editor.org/rfc/rfc1738),
+[RFC3986](https://www.rfc-editor.org/rfc/rfc3986), and the [Freedesktop File URI
+spec](https://www.freedesktop.org/wiki/Specifications/file-uri-spec/).
+"""
+function uripath(path::String)
+    percent_escape(s) =
+        '%' * join(map(b -> string(b, base=16), codeunits(s)), '%')
+    encode_uri_component(s) =
+        replace(s, r"[^A-Za-z0-9\-_.~]+" => percent_escape)
+    string("file://", gethostname(), '/',
+           join(map(encode_uri_component,
+                    split(abspath(path), path_separator_re, keepempty=false)),
+                '/'))
+end
+
+uripath(path::AbstractString) = uripath(String(path))

test/path.jl

@@ -311,6 +311,18 @@
         test_relpath()
     end
 
+    @testset "uripath" begin
+        host = gethostname()
+        absprefix = if Sys.iswindows() "C:$sep" else "$sep" end
+        @test Base.Filesystem.uripath("$(absprefix)some$(sep)file.txt") == "file://$host/some/file.txt"
+        @test Base.Filesystem.uripath("$(absprefix)another$(sep)$(sep)folder$(sep)file.md") == "file://$host/another/folder/file.md"
+        @test Base.Filesystem.uripath("$(absprefix)some file with ^odd% chars") == "file://$host/some%20file%20with%20%5eodd%25%20chars"
+        @test Base.Filesystem.uripath("$(absprefix)weird chars like @#&()[]{}") == "file://$host/weird%20chars%20like%20%40%23%26%28%29%5b%5d%7b%7d"
+        @test Base.Filesystem.uripath("$absprefix") == "file://$host/"
+        @test Base.Filesystem.uripath(".") == Base.Filesystem.uripath(pwd())
+        @test Base.Filesystem.uripath("$(absprefix)unicode$(sep)Δεδομένα") == "file://$host/unicode/%ce%94%ce%b5%ce%b4%ce%bf%ce%bc%ce%ad%ce%bd%ce%b1"
+    end
+
     if Sys.iswindows()
         @testset "issue #23646" begin
             @test lowercase(relpath("E:\\a\\b", "C:\\c")) == "e:\\a\\b"