Add Hugo Modules

This commit implements Hugo Modules.

This is a broad subject, but some keywords include:

* A new `module` configuration section where you can import almost anything. You can configure both your own file mounts nd the file mounts of the modules you import. This is the new recommended way of configuring what you earlier put in `configDir`, `staticDir` etc. And it also allows you to mount folders in non-Hugo-projects, e.g. the `SCSS` folder in the Bootstrap GitHub project.
* A module consists of a set of mounts to the standard 7 component types in Hugo: `static`, `content`, `layouts`, `data`, `assets`, `i18n`, and `archetypes`. Yes, Theme Components can now include content, which should be very useful, especially in bigger multilingual projects.
* Modules not in your local file cache will be downloaded automatically and even "hot replaced" while the server is running.
* Hugo Modules supports and encourages semver versioned modules, and uses the minimal version selection algorithm to resolve versions.
* A new set of CLI commands are provided to manage all of this: `hugo mod init`,  `hugo mod get`,  `hugo mod graph`,  `hugo mod tidy`, and  `hugo mod vendor`.

All of the above is backed by Go Modules.

Fixes #5973
Fixes #5996
Fixes #6010
Fixes #5911
Fixes #5940
Fixes #6074
Fixes #6082
Fixes #6092

1 files changed, 189 insertions, 0 deletions

diff --git a/commands/mod.go b/commands/mod.go
new file mode 100644
index 000000000..861704e35
--- /dev/null
+++ b/commands/mod.go
@@ -0,0 +1,189 @@
+// Copyright 2019 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package commands
+
+import (
+	"os"
+	"strings"
+
+	"github.com/gohugoio/hugo/modules"
+	"github.com/spf13/cobra"
+)
+
+var _ cmder = (*modCmd)(nil)
+
+type modCmd struct {
+	*baseBuilderCmd
+}
+
+func (b *commandsBuilder) newModCmd() *modCmd {
+	c := &modCmd{}
+
+	const commonUsage = `
+Note that Hugo will always start out by resolving the components defined in the site
+configuration, provided by a _vendor directory (if no --ignoreVendor flag provided),
+Go Modules, or a folder inside the themes directory, in that order.
+
+See https://gohugo.io/hugo-modules/ for more information.
+
+`
+
+	cmd := &cobra.Command{
+		Use:   "mod",
+		Short: "Various Hugo Modules helpers.",
+		Long: `Various helpers to help manage the modules in your project's dependency graph.
+
+Most operations here requires a Go version installed on your system (>= Go 1.12) and the relevant VCS client (typically Git).
+This is not needed if you only operate on modules inside /themes or if you have vendored them via "hugo mod vendor".
+
+` + commonUsage,
+
+		RunE: nil,
+	}
+
+	cmd.AddCommand(
+		&cobra.Command{
+			Use:                "get",
+			DisableFlagParsing: true,
+			Short:              "Resolves dependencies in your current Hugo Project.",
+			Long: `
+Resolves dependencies in your current Hugo Project.
+
+Some examples:
+
+Install the latest version possible for a given module:
+
+    hugo mod get github.com/gohugoio/testshortcodes
+    
+Install a specific version:
+
+    hugo mod get github.com/gohugoio/[email protected]
+
+Install the latest versions of all module dependencies:
+
+    hugo mod get -u
+
+Run "go help get" for more information. All flags available for "go get" is also relevant here.
+` + commonUsage,
+			RunE: func(cmd *cobra.Command, args []string) error {
+				return c.withModsClient(false, func(c *modules.Client) error {
+					// We currently just pass on the flags we get to Go and
+					// need to do the flag handling manually.
+					if len(args) == 1 && strings.Contains(args[0], "-h") {
+						return cmd.Help()
+					}
+					return c.Get(args...)
+				})
+			},
+		},
+		&cobra.Command{
+			Use:   "graph",
+			Short: "Print a module dependency graph.",
+			Long: `Print a module dependency graph with information about module status (disabled, vendored).
+Note that for vendored modules, that is the version listed and not the one from go.mod.
+`,
+			RunE: func(cmd *cobra.Command, args []string) error {
+				return c.withModsClient(true, func(c *modules.Client) error {
+					return c.Graph(os.Stdout)
+				})
+			},
+		},
+		&cobra.Command{
+			Use:   "init",
+			Short: "Initialize this project as a Hugo Module.",
+			Long: `Initialize this project as a Hugo Module.
+It will try to guess the module path, but you may help by passing it as an argument, e.g:
+
+    hugo mod init github.com/gohugoio/testshortcodes
+
+Note that Hugo Modules supports multi-module projects, so you can initialize a Hugo Module
+inside a subfolder on GitHub, as one example.
+`,
+			RunE: func(cmd *cobra.Command, args []string) error {
+				var path string
+				if len(args) >= 1 {
+					path = args[0]
+				}
+				return c.withModsClient(false, func(c *modules.Client) error {
+					return c.Init(path)
+				})
+			},
+		},
+		&cobra.Command{
+			Use:   "vendor",
+			Short: "Vendor all module dependencies into the _vendor directory.",
+			Long: `Vendor all module dependencies into the _vendor directory.
+
+If a module is vendored, that is where Hugo will look for it's dependencies.
+`,
+			RunE: func(cmd *cobra.Command, args []string) error {
+				return c.withModsClient(true, func(c *modules.Client) error {
+					return c.Vendor()
+				})
+			},
+		},
+		&cobra.Command{
+			Use:   "tidy",
+			Short: "Remove unused entries in go.mod and go.sum.",
+			RunE: func(cmd *cobra.Command, args []string) error {
+				return c.withModsClient(true, func(c *modules.Client) error {
+					return c.Tidy()
+				})
+			},
+		},
+		&cobra.Command{
+			Use:   "clean",
+			Short: "Delete the entire Hugo Module cache.",
+			Long: `Delete the entire Hugo Module cache.
+
+Note that after you run this command, all of your dependencies will be re-downloaded next time you run "hugo".
+
+Also note that if you configure a positive maxAge for the "modules" file cache, it will also be cleaned as part of "hugo --gc".
+ 
+`,
+			RunE: func(cmd *cobra.Command, args []string) error {
+				com, err := c.initConfig(true)
+				if err != nil {
+					return err
+				}
+
+				_, err = com.hugo.FileCaches.ModulesCache().Prune(true)
+				return err
+
+			},
+		},
+	)
+
+	c.baseBuilderCmd = b.newBuilderCmd(cmd)
+
+	return c
+
+}
+
+func (c *modCmd) withModsClient(failOnMissingConfig bool, f func(*modules.Client) error) error {
+	com, err := c.initConfig(failOnMissingConfig)
+	if err != nil {
+		return err
+	}
+
+	return f(com.hugo.ModulesClient)
+}
+
+func (c *modCmd) initConfig(failOnNoConfig bool) (*commandeer, error) {
+	com, err := initializeConfig(failOnNoConfig, false, &c.hugoBuilderCommon, c, nil)
+	if err != nil {
+		return nil, err
+	}
+	return com, nil
+}