hugolib: Refactor/-work the permalink/target path logic

This is a pretty fundamental change in Hugo, but absolutely needed if we should have any hope of getting "multiple outputs" done.

This commit's goal is to say:

* Every file target path is created by `createTargetPath`, i.e. one function for all.
* That function takes every page and site parameter into account, to avoid fragile string parsing to uglify etc. later on.
* The path creation logic has full test coverage.
* All permalinks, paginator URLs etc. are then built on top of that same logic.

Fixes #1252
Fixes #2110
Closes #2374
Fixes #1885
Fixes #3102
Fixes #3179
Fixes #1641
Fixes #1989

helpers/pathspec.go

@@ -22,6 +22,8 @@ import (
 
 // PathSpec holds methods that decides how paths in URLs and files in Hugo should look like.
 type PathSpec struct {
+	BaseURL
+
 	disablePathToLower bool
 	removePathAccents  bool
 	uglyURLs           bool
@@ -32,8 +34,7 @@ type PathSpec struct {
 	// pagination path handling
 	paginatePath string
 
-	baseURL string
-	theme   string
+	theme string
 
 	// Directories
 	themesDir  string
@@ -61,6 +62,9 @@ func (p PathSpec) String() string {
 // NewPathSpec creats a new PathSpec from the given filesystems and Language.
 func NewPathSpec(fs *hugofs.Fs, cfg config.Provider) *PathSpec {
 
+	// TODO(bep) output error handling
+	baseURL, _ := newBaseURLFromString(cfg.GetString("baseURL"))
+
 	ps := &PathSpec{
 		fs:                             fs,
 		disablePathToLower:             cfg.GetBool("disablePathToLower"),
@@ -71,7 +75,7 @@ func NewPathSpec(fs *hugofs.Fs, cfg config.Provider) *PathSpec {
 		defaultContentLanguageInSubdir: cfg.GetBool("defaultContentLanguageInSubdir"),
 		defaultContentLanguage:         cfg.GetString("defaultContentLanguage"),
 		paginatePath:                   cfg.GetString("paginatePath"),
-		baseURL:                        cfg.GetString("baseURL"),
+		BaseURL:                        baseURL,
 		themesDir:                      cfg.GetString("themesDir"),
 		layoutDir:                      cfg.GetString("layoutDir"),
 		workingDir:                     cfg.GetString("workingDir"),