Add "hugo mod npm pack"

This commit also introduces a convention where these common JS config files, including `package.hugo.json`, gets mounted into:

```
assets/_jsconfig
´``

These files mapped to their real filename will be added to the environment when running PostCSS, Babel etc., so you can do `process.env.HUGO_FILE_TAILWIND_CONFIG_JS` to resolve the real filename.

But do note that `assets` is a composite/union filesystem, so if your config file is not meant to be overridden, name them something specific.

This commit also adds adds `workDir/node_modules` to `NODE_PATH` and `HUGO_WORKDIR` to the env when running the JS tools above.

Fixes #7644
Fixes #7656
Fixes #7675

3 files changed, 194 insertions, 6 deletions

diff --git a/hugolib/filesystems/basefs.go b/hugolib/filesystems/basefs.go
index 57a95a037..76d49055c 100644
--- a/hugolib/filesystems/basefs.go
+++ b/hugolib/filesystems/basefs.go
@@ -49,6 +49,9 @@ type BaseFs struct {
 	// SourceFilesystems contains the different source file systems.
 	*SourceFilesystems
 
+	// The project source.
+	SourceFs afero.Fs
+
 	// The filesystem used to publish the rendered site.
 	// This usually maps to /my-project/public.
 	PublishFs afero.Fs
@@ -100,6 +103,23 @@ func (b *BaseFs) RelContentDir(filename string) string {
 	return filename
 }
 
+// ResolveJSConfigFile resolves the JS-related config file to a absolute
+// filename. One example of such would be postcss.config.js.
+func (fs *BaseFs) ResolveJSConfigFile(name string) string {
+	// First look in assets/_jsconfig
+	fi, err := fs.Assets.Fs.Stat(filepath.Join(files.FolderJSConfig, name))
+	if err == nil {
+		return fi.(hugofs.FileMetaInfo).Meta().Filename()
+	}
+	// Fall back to the work dir.
+	fi, err = fs.Work.Stat(name)
+	if err == nil {
+		return fi.(hugofs.FileMetaInfo).Meta().Filename()
+	}
+
+	return ""
+}
+
 // SourceFilesystems contains the different source file systems. These can be
 // composite file systems (theme and project etc.), and they have all root
 // set to the source type the provides: data, i18n, static, layouts.
@@ -346,8 +366,10 @@ func NewBase(p *paths.Paths, logger *loggers.Logger, options ...func(*BaseFs) er
 	}
 
 	publishFs := hugofs.NewBaseFileDecorator(afero.NewBasePathFs(fs.Destination, p.AbsPublishDir))
+	sourceFs := hugofs.NewBaseFileDecorator(afero.NewBasePathFs(fs.Source, p.WorkingDir))
 
 	b := &BaseFs{
+		SourceFs:  sourceFs,
 		PublishFs: publishFs,
 	}
 
@@ -696,11 +718,16 @@ type filesystemsCollector struct {
 
 func (c *filesystemsCollector) addDirs(rfs *hugofs.RootMappingFs) {
 	for _, componentFolder := range files.ComponentFolders {
-		dirs, err := rfs.Dirs(componentFolder)
+		c.addDir(rfs, componentFolder)
+	}
 
-		if err == nil {
-			c.overlayDirs[componentFolder] = append(c.overlayDirs[componentFolder], dirs...)
-		}
+}
+
+func (c *filesystemsCollector) addDir(rfs *hugofs.RootMappingFs, componentFolder string) {
+	dirs, err := rfs.Dirs(componentFolder)
+
+	if err == nil {
+		c.overlayDirs[componentFolder] = append(c.overlayDirs[componentFolder], dirs...)
 	}
 }
 
diff --git a/hugolib/hugo_modules_test.go b/hugolib/hugo_modules_test.go
index 0ed4fceb0..c3358a0c2 100644
--- a/hugolib/hugo_modules_test.go
+++ b/hugolib/hugo_modules_test.go
@@ -22,6 +22,8 @@ import (
 	"testing"
 	"time"
 
+	"github.com/gohugoio/hugo/modules/npm"
+
 	"github.com/gohugoio/hugo/common/loggers"
 
 	"github.com/spf13/afero"
@@ -38,7 +40,6 @@ import (
 	"github.com/spf13/viper"
 )
 
-// https://github.com/gohugoio/hugo/issues/6730
 func TestHugoModulesVariants(t *testing.T) {
 	if !isCI() {
 		t.Skip("skip (relative) long running modules test when running locally")
@@ -60,8 +61,10 @@ path="github.com/gohugoio/hugoTestModule2"
 
 	newTestBuilder := func(t testing.TB, moduleOpts string) (*sitesBuilder, func()) {
 		b := newTestSitesBuilder(t)
-		workingDir, clean, err := htesting.CreateTempDir(hugofs.Os, "hugo-modules-variants")
+		tempDir, clean, err := htesting.CreateTempDir(hugofs.Os, "hugo-modules-variants")
 		b.Assert(err, qt.IsNil)
+		workingDir := filepath.Join(tempDir, "myhugosite")
+		b.Assert(os.MkdirAll(workingDir, 0777), qt.IsNil)
 		b.Fs = hugofs.NewDefault(viper.New())
 		b.WithWorkingDir(workingDir).WithConfigFile("toml", createConfig(workingDir, moduleOpts))
 		b.WithTemplates(
@@ -129,6 +132,158 @@ JS imported in module: |
 `)
 	})
 
+	t.Run("Create package.json", func(t *testing.T) {
+
+		b, clean := newTestBuilder(t, "")
+		defer clean()
+
+		b.WithSourceFile("package.json", `{
+		"name": "mypack",
+		"version": "1.2.3",
+        "scripts": {},
+          "dependencies": {
+        	"nonon": "error"
+        	}
+}`)
+
+		b.WithSourceFile("package.hugo.json", `{
+		"name": "mypack",
+		"version": "1.2.3",
+        "scripts": {},
+          "dependencies": {
+        	"foo": "1.2.3"
+        	},
+        "devDependencies": {
+                "postcss-cli": "7.8.0",
+                "tailwindcss": "1.8.0"
+ 
+        }
+}`)
+
+		b.Build(BuildCfg{})
+		b.Assert(npm.Pack(b.H.BaseFs.SourceFs, b.H.BaseFs.Assets.Dirs), qt.IsNil)
+
+		b.AssertFileContentFn("package.json", func(s string) bool {
+			return s == `{
+ "comments": {
+  "dependencies": {
+   "foo": "project",
+   "react-dom": "github.com/gohugoio/hugoTestModule2"
+  },
+  "devDependencies": {
+   "@babel/cli": "github.com/gohugoio/hugoTestModule2",
+   "@babel/core": "github.com/gohugoio/hugoTestModule2",
+   "@babel/preset-env": "github.com/gohugoio/hugoTestModule2",
+   "postcss-cli": "project",
+   "tailwindcss": "project"
+  }
+ },
+ "dependencies": {
+  "foo": "1.2.3",
+  "react-dom": "^16.13.1"
+ },
+ "devDependencies": {
+  "@babel/cli": "7.8.4",
+  "@babel/core": "7.9.0",
+  "@babel/preset-env": "7.9.5",
+  "postcss-cli": "7.8.0",
+  "tailwindcss": "1.8.0"
+ },
+ "name": "mypack",
+ "scripts": {},
+ "version": "1.2.3"
+}`
+		})
+	})
+
+	t.Run("Create package.json, no default", func(t *testing.T) {
+
+		b, clean := newTestBuilder(t, "")
+		defer clean()
+
+		b.WithSourceFile("package.json", `{
+		"name": "mypack",
+		"version": "1.2.3",
+        "scripts": {},
+          "dependencies": {
+           "moo": "1.2.3"
+        	}
+}`)
+
+		b.Build(BuildCfg{})
+		b.Assert(npm.Pack(b.H.BaseFs.SourceFs, b.H.BaseFs.Assets.Dirs), qt.IsNil)
+
+		b.AssertFileContentFn("package.json", func(s string) bool {
+			return s == `{
+ "comments": {
+  "dependencies": {
+   "moo": "project",
+   "react-dom": "github.com/gohugoio/hugoTestModule2"
+  },
+  "devDependencies": {
+   "@babel/cli": "github.com/gohugoio/hugoTestModule2",
+   "@babel/core": "github.com/gohugoio/hugoTestModule2",
+   "@babel/preset-env": "github.com/gohugoio/hugoTestModule2",
+   "postcss-cli": "github.com/gohugoio/hugoTestModule2",
+   "tailwindcss": "github.com/gohugoio/hugoTestModule2"
+  }
+ },
+ "dependencies": {
+  "moo": "1.2.3",
+  "react-dom": "^16.13.1"
+ },
+ "devDependencies": {
+  "@babel/cli": "7.8.4",
+  "@babel/core": "7.9.0",
+  "@babel/preset-env": "7.9.5",
+  "postcss-cli": "7.1.0",
+  "tailwindcss": "1.2.0"
+ },
+ "name": "mypack",
+ "scripts": {},
+ "version": "1.2.3"
+}`
+		})
+	})
+
+	t.Run("Create package.json, no default, no package.json", func(t *testing.T) {
+
+		b, clean := newTestBuilder(t, "")
+		defer clean()
+
+		b.Build(BuildCfg{})
+		b.Assert(npm.Pack(b.H.BaseFs.SourceFs, b.H.BaseFs.Assets.Dirs), qt.IsNil)
+
+		b.AssertFileContentFn("package.json", func(s string) bool {
+			return s == `{
+ "comments": {
+  "dependencies": {
+   "react-dom": "github.com/gohugoio/hugoTestModule2"
+  },
+  "devDependencies": {
+   "@babel/cli": "github.com/gohugoio/hugoTestModule2",
+   "@babel/core": "github.com/gohugoio/hugoTestModule2",
+   "@babel/preset-env": "github.com/gohugoio/hugoTestModule2",
+   "postcss-cli": "github.com/gohugoio/hugoTestModule2",
+   "tailwindcss": "github.com/gohugoio/hugoTestModule2"
+  }
+ },
+ "dependencies": {
+  "react-dom": "^16.13.1"
+ },
+ "devDependencies": {
+  "@babel/cli": "7.8.4",
+  "@babel/core": "7.9.0",
+  "@babel/preset-env": "7.9.5",
+  "postcss-cli": "7.1.0",
+  "tailwindcss": "1.2.0"
+ },
+ "name": "myhugosite",
+ "version": "0.1.0"
+}`
+		})
+	})
+
 }
 
 // TODO(bep) this fails when testmodBuilder is also building ...
diff --git a/hugolib/resource_chain_test.go b/hugolib/resource_chain_test.go
index 64484f1f4..7573199aa 100644
--- a/hugolib/resource_chain_test.go
+++ b/hugolib/resource_chain_test.go
@@ -873,6 +873,10 @@ func TestResourceChainPostCSS(t *testing.T) {
 
 	postcssConfig := `
 console.error("Hugo Environment:", process.env.HUGO_ENVIRONMENT );
+// https://github.com/gohugoio/hugo/issues/7656
+console.error("package.json:", process.env.HUGO_FILE_PACKAGE_JSON );
+console.error("PostCSS Config File:", process.env.HUGO_FILE_POSTCSS_CONFIG_JS );
+
 
 module.exports = {
   plugins: [
@@ -954,6 +958,8 @@ class-in-b {
 
 	// Make sure Node sees this.
 	b.Assert(logBuf.String(), qt.Contains, "Hugo Environment: production")
+	b.Assert(logBuf.String(), qt.Contains, fmt.Sprintf("PostCSS Config File: %s/postcss.config.js", workDir))
+	b.Assert(logBuf.String(), qt.Contains, fmt.Sprintf("package.json: %s/package.json", workDir))
 
 	b.AssertFileContent("public/index.html", `
 Styles RelPermalink: /css/styles.css