Allow anchor <doc:#heading> within same article (#652)

Author: natikgadzhi

Sources/SwiftDocC/Infrastructure/Link Resolution/PathHierarchy.swift

@@ -764,10 +764,16 @@ extension PathHierarchy {
         let isAbsolute = path.first == "/"
             || String(components.first ?? "") == NodeURLGenerator.Path.documentationFolderName
             || String(components.first ?? "") == NodeURLGenerator.Path.tutorialsFolderName
-       
+
+        // If there is a # character in the last component, split that into two components
         if let hashIndex = components.last?.firstIndex(of: "#") {
             let last = components.removeLast()
-            components.append(last[..<hashIndex])
+            // Allow anrhor-only links where there's nothing before #.
+            // In case the pre-# part is empty, and we're omitting empty components, don't add it in.
+            let pathName = last[..<hashIndex]
+            if !pathName.isEmpty || !omittingEmptyComponents {
+                components.append(pathName)
+            }
 
             let fragment = String(last[hashIndex...].dropFirst())
             return (components.map(Self.parse(pathComponent:)) + [PathComponent(full: fragment, name: fragment, kind: nil, hash: nil)], isAbsolute)

Tests/SwiftDocCTests/Infrastructure/PathHierarchyTests.swift

@@ -1133,6 +1133,30 @@ class PathHierarchyTests: XCTestCase {
         XCTAssertNil(articleNode.symbol, "General documentation link find the article")
     }
 
+    func testArticleSelfAnchorLinks() throws {
+        try XCTSkipUnless(LinkResolutionMigrationConfiguration.shouldUseHierarchyBasedLinkResolver)
+        let (_, _, context) = try testBundleAndContext(copying: "MixedLanguageFramework") { url in
+            try """
+            # ArticleWithHeading
+
+            ## TestTargetHeading
+
+            This article has the same path as a symbol. See also:
+            - <doc:TestTargetHeading>
+            - <doc:#TestTargetHeading>
+
+            """.write(to: url.appendingPathComponent("ArticleWithHeading.md"), atomically: true, encoding: .utf8)
+        }
+
+        let tree = try XCTUnwrap(context.hierarchyBasedLinkResolver?.pathHierarchy)
+        let articleNode = try tree.findNode(path: "/MixedLanguageFramework/ArticleWithHeading", onlyFindSymbols: false)
+
+        let linkNode = try tree.find(path: "TestTargetHeading", parent: articleNode.identifier, onlyFindSymbols: false)
+        let anchorLinkNode = try tree.find(path: "#TestTargetHeading", parent: articleNode.identifier, onlyFindSymbols: false)
+        XCTAssertNotNil(linkNode)
+        XCTAssertNotNil(anchorLinkNode)
+    }
+
     func testOverloadedSymbols() throws {
         try XCTSkipUnless(LinkResolutionMigrationConfiguration.shouldUseHierarchyBasedLinkResolver)
         let (_, context) = try testBundleAndContext(named: "OverloadedSymbols")
@@ -1555,6 +1579,7 @@ class PathHierarchyTests: XCTestCase {
         assertParsedPathComponents("first/", [("first", nil, nil)])
         assertParsedPathComponents("first//second", [("first", nil, nil), ("second", nil, nil)])
         assertParsedPathComponents("first/second#third", [("first", nil, nil), ("second", nil, nil), ("third", nil, nil)])
+        assertParsedPathComponents("#first", [("first", nil, nil)])
 
         // Check disambiguation
         assertParsedPathComponents("path-hash", [("path", nil, "hash")])