fix(internal/godocfx): use correct anchor links (#3738)

This works by pre-processing the package and generating all of the correct anchor links. Then, when converting an ID to a link, we check if the ID is listed in the map of anchors.

It's possible there will be some duplication between IDs. But, that is already an issue because there is no way to know which one is correct to link to. An alternative would be to set the anchor for any duplicated links to `""` so they don't link at all. In practice, I don't think this is an issue. So, I left it as-is and we can revisit later if needed.

Fixes #3737.

internal/godocfx/parse.go

@@ -34,6 +34,7 @@ import (
 	"log"
 	"os"
 	"path/filepath"
+	"regexp"
 	"sort"
 	"strconv"
 	"strings"
@@ -155,7 +156,7 @@ func parse(glob string, workingDir string, optionalExtraFiles []string) (*result
 	// Once the files are grouped by package, process each package
 	// independently.
 	for _, pi := range pkgInfos {
-		link := newLinker(pi.pkg.Imports, pi.importRenames)
+		link := newLinker(pi)
 		topLevelDecls := pkgsite.TopLevelDecls(pi.doc)
 		pkgItem := &item{
 			UID:      pi.doc.ImportPath,
@@ -183,7 +184,7 @@ func parse(glob string, workingDir string, optionalExtraFiles []string) (*result
 				Type:    "const",
 				Summary: c.Doc,
 				Langs:   onlyGo,
-				Syntax:  syntax{Content: pkgsite.PrintType(pi.fset, c.Decl, toURL, topLevelDecls)},
+				Syntax:  syntax{Content: pkgsite.PrintType(pi.fset, c.Decl, link.toURL, topLevelDecls)},
 			})
 		}
 		for _, v := range pi.doc.Vars {
@@ -199,7 +200,7 @@ func parse(glob string, workingDir string, optionalExtraFiles []string) (*result
 				Type:    "variable",
 				Summary: v.Doc,
 				Langs:   onlyGo,
-				Syntax:  syntax{Content: pkgsite.PrintType(pi.fset, v.Decl, toURL, topLevelDecls)},
+				Syntax:  syntax{Content: pkgsite.PrintType(pi.fset, v.Decl, link.toURL, topLevelDecls)},
 			})
 		}
 		for _, t := range pi.doc.Types {
@@ -213,7 +214,7 @@ func parse(glob string, workingDir string, optionalExtraFiles []string) (*result
 				Type:     "type",
 				Summary:  t.Doc,
 				Langs:    onlyGo,
-				Syntax:   syntax{Content: pkgsite.PrintType(pi.fset, t.Decl, toURL, topLevelDecls)},
+				Syntax:   syntax{Content: pkgsite.PrintType(pi.fset, t.Decl, link.toURL, topLevelDecls)},
 				Examples: processExamples(t.Examples, pi.fset),
 			}
 			// Note: items are added as page.Children, rather than
@@ -232,7 +233,7 @@ func parse(glob string, workingDir string, optionalExtraFiles []string) (*result
 					Type:    "const",
 					Summary: c.Doc,
 					Langs:   onlyGo,
-					Syntax:  syntax{Content: pkgsite.PrintType(pi.fset, c.Decl, toURL, topLevelDecls)},
+					Syntax:  syntax{Content: pkgsite.PrintType(pi.fset, c.Decl, link.toURL, topLevelDecls)},
 				})
 			}
 			for _, v := range t.Vars {
@@ -248,7 +249,7 @@ func parse(glob string, workingDir string, optionalExtraFiles []string) (*result
 					Type:    "variable",
 					Summary: v.Doc,
 					Langs:   onlyGo,
-					Syntax:  syntax{Content: pkgsite.PrintType(pi.fset, v.Decl, toURL, topLevelDecls)},
+					Syntax:  syntax{Content: pkgsite.PrintType(pi.fset, v.Decl, link.toURL, topLevelDecls)},
 				})
 			}
 
@@ -313,18 +314,84 @@ type linker struct {
 	// Behavior is undefined when a single import has different names in
 	// different files.
 	imports map[string]string
+
+	// idToAnchor is a map from an ID to the anchor URL for that ID.
+	idToAnchor map[string]string
 }
 
-func newLinker(rawImports map[string]*packages.Package, importSyntax map[string]string) *linker {
+func newLinker(pi pkgInfo) *linker {
 	imports := map[string]string{}
-	for path, pkg := range rawImports {
+	for path, pkg := range pi.pkg.Imports {
 		name := pkg.Name
-		if rename := importSyntax[path]; rename != "" {
+		if rename := pi.importRenames[path]; rename != "" {
 			name = rename
 		}
 		imports[name] = path
 	}
-	return &linker{imports: imports}
+
+	idToAnchor := buildIDToAnchor(pi)
+
+	return &linker{imports: imports, idToAnchor: idToAnchor}
+}
+
+// nonWordRegex is based on
+// https://github.com/googleapis/doc-templates/blob/70eba5908e7b9aef5525d0f1f24194ae750f267e/third_party/docfx/templates/devsite/common.js#L27-L30.
+var nonWordRegex = regexp.MustCompile("\\W")
+
+func buildIDToAnchor(pi pkgInfo) map[string]string {
+	idToAnchor := map[string]string{}
+	idToAnchor[pi.doc.ImportPath] = pi.doc.ImportPath
+
+	for _, c := range pi.doc.Consts {
+		commaID := strings.Join(c.Names, ",")
+		uid := pi.doc.ImportPath + "." + commaID
+		for _, name := range c.Names {
+			idToAnchor[name] = uid
+		}
+	}
+	for _, v := range pi.doc.Vars {
+		commaID := strings.Join(v.Names, ",")
+		uid := pi.doc.ImportPath + "." + commaID
+		for _, name := range v.Names {
+			idToAnchor[name] = uid
+		}
+	}
+	for _, f := range pi.doc.Funcs {
+		uid := pi.doc.ImportPath + "." + f.Name
+		idToAnchor[f.Name] = uid
+	}
+	for _, t := range pi.doc.Types {
+		uid := pi.doc.ImportPath + "." + t.Name
+		idToAnchor[t.Name] = uid
+		for _, c := range t.Consts {
+			commaID := strings.Join(c.Names, ",")
+			uid := pi.doc.ImportPath + "." + commaID
+			for _, name := range c.Names {
+				idToAnchor[name] = uid
+			}
+		}
+		for _, v := range t.Vars {
+			commaID := strings.Join(v.Names, ",")
+			uid := pi.doc.ImportPath + "." + commaID
+			for _, name := range v.Names {
+				idToAnchor[name] = uid
+			}
+		}
+		for _, f := range t.Funcs {
+			uid := pi.doc.ImportPath + "." + t.Name + "." + f.Name
+			idToAnchor[f.Name] = uid
+		}
+		for _, m := range t.Methods {
+			uid := pi.doc.ImportPath + "." + t.Name + "." + m.Name
+			idToAnchor[m.Name] = uid
+		}
+	}
+
+	for id, anchor := range idToAnchor {
+		idToAnchor[id] = nonWordRegex.ReplaceAllString(anchor, "_")
+	}
+
+	return idToAnchor
 }
 
 func (l *linker) linkify(s string) string {
@@ -342,11 +409,11 @@ func (l *linker) linkify(s string) string {
 		// If s is not exported, it's probably a builtin.
 		if !token.IsExported(s) {
 			if doc.IsPredeclared(s) {
-				return href(toURL("builtin", s), s)
+				return href(l.toURL("builtin", s), s)
 			}
 			return fmt.Sprintf("%s%s", prefix, s)
 		}
-		return fmt.Sprintf("%s%s", prefix, href(toURL("", s), s))
+		return fmt.Sprintf("%s%s", prefix, href(l.toURL("", s), s))
 	}
 	// Otherwise, it's in another package.
 	split := strings.Split(s, ".")
@@ -362,14 +429,17 @@ func (l *linker) linkify(s string) string {
 		return fmt.Sprintf("%s%s", prefix, s)
 	}
 	name := split[1]
-	return fmt.Sprintf("%s%s.%s", prefix, href(toURL(pkgPath, ""), pkg), href(toURL(pkgPath, name), name))
+	return fmt.Sprintf("%s%s.%s", prefix, href(l.toURL(pkgPath, ""), pkg), href(l.toURL(pkgPath, name), name))
 }
 
 // TODO: link to the right baseURL, with the right module name and version
 // pattern.
-func toURL(pkg, name string) string {
+func (l *linker) toURL(pkg, name string) string {
 	if pkg == "" {
-		return fmt.Sprintf("#%s", strings.ToLower(name))
+		if anchor := l.idToAnchor[name]; anchor != "" {
+			name = anchor
+		}
+		return fmt.Sprintf("#%s", name)
 	}
 	baseURL := "https://pkg.go.dev"
 	if name == "" {