Preserve relative URL path semantics.

lib/protocol/url/path.rb

@@ -372,12 +372,25 @@ def relative(from)
 					common_length = i + 1
 				end
 
+				# Preserve the final segment when the target names the containing directory as a file:
+				if common_length > 0 && common_length == target_segments.size && target_segments.last != ""
+					common_length -= 1
+				end
+
 				# Calculate how many levels to go up
 				up_levels = from_segments.size - common_length
 
 				# Build the relative path segments
 				relative_segments = [".."] * up_levels + target_segments[common_length..-1]
 
+				# An empty reference identifies the current document, so identify the current directory explicitly:
+				if relative_segments == [""]
+					relative_segments = [".", ""]
+				elsif relative_segments.first&.include?(":")
+					# A colon in the first segment would be interpreted as a URI scheme:
+					relative_segments.unshift(".")
+				end
+
 				return Path.new(nil, relative_segments)
 			end
 

releases.md

@@ -1,5 +1,9 @@
 # Releases
 
+## Unreleased
+
+  - Preserve directory and file semantics when generating relative URL paths.
+
 ## v0.15.0
 
   - Add `Protocol::URL::Relative#relative_to` for expressing root-relative URLs relative to a base path.

test/protocol/url/path.rb

@@ -509,6 +509,22 @@
 			expect(Protocol::URL::Path.relative("/docs/", "/docs/api/reference.html")).to be == "../"
 		end
 
+		it "identifies the current directory explicitly" do
+			expect(Protocol::URL::Path.relative("/docs/", "/docs/index.html")).to be == "./"
+		end
+
+		it "calculates relative path to the root directory" do
+			expect(Protocol::URL::Path.relative("/", "/index.html")).to be == "./"
+		end
+
+		it "distinguishes a file from its containing directory" do
+			expect(Protocol::URL::Path.relative("/docs", "/docs/index.html")).to be == "../docs"
+		end
+
+		it "disambiguates a colon in the first segment" do
+			expect(Protocol::URL::Path.relative("/docs/this:that", "/docs/index.html")).to be == "./this:that"
+		end
+
 		it "calculates relative path with multiple levels up" do
 			expect(Protocol::URL::Path.relative("/a/file.txt", "/x/y/z/")).to be == "../../../a/file.txt"
 		end

test/protocol/url/relative.rb

@@ -218,6 +218,20 @@
 			expect(url.relative_to("/index").path).to be == Protocol::URL::Path["files/a%2Fb"]
 		end
 
+		it "identifies the root directory explicitly" do
+			url = Protocol::URL::Relative.new("/", "q=ruby", "examples")
+
+			expect(url.relative_to("/index").to_s).to be == "./?q=ruby#examples"
+		end
+
+		it "disambiguates a colon in the first segment" do
+			url = Protocol::URL::Relative.new("/docs/this:that")
+			relative_url = url.relative_to("/docs/index")
+
+			expect(relative_url.to_s).to be == "./this:that"
+			expect(Protocol::URL[relative_url.to_s]).to be_a(Protocol::URL::Relative)
+		end
+
 		it "returns already-relative URLs unchanged" do
 			url = Protocol::URL::Relative.new("../guide", "q=ruby", "examples")