resources: Add basic @import support to resources.PostCSS

This commit also makes the HUGO_ENVIRONMENT environment variable available to Node.

Fixes #6957
Fixes #6961

5 files changed, 313 insertions, 1 deletions

diff --git a/docs/content/en/hugo-pipes/postcss.md b/docs/content/en/hugo-pipes/postcss.md
index a0a673798..a7ba097fa 100755
--- a/docs/content/en/hugo-pipes/postcss.md
+++ b/docs/content/en/hugo-pipes/postcss.md
@@ -39,6 +39,12 @@ config [string]
 noMap [bool]
 : Default is `true`. Disable the default inline sourcemaps
 
+inlineImports [bool] {{< new-in "0.66.0" >}}
+: Default is `false`. Enable inlining of @import statements. It does so recursively, but will only import a file once.
+URL imports (e.g. `@import url('https://fonts.googleapis.com/css?family=Open+Sans&display=swap');`) and imports with media queries will be ignored.
+Note that this import routine does not care about the CSS spec, so you can have @import anywhere in the file.
+Hugo will look for imports relative to the module mount and will respect theme overrides.
+
 _If no configuration file is used:_
 
 use [string]
@@ -55,4 +61,21 @@ syntax [string]
 
 ```go-html-template
 {{ $style := resources.Get "css/main.css" | resources.PostCSS (dict "config" "customPostCSS.js" "noMap" true) }}
+```
+
+## Check Hugo Environment from postcss.config.js
+
+{{< new-in "0.66.0" >}}
+
+The current Hugo environment name (set by `--environment` or in config or OS environment) is available in the Node context, which allows constructs like this:
+
+```js
+module.exports = {
+  plugins: [
+    require('autoprefixer'),
+    ...process.env.HUGO_ENVIRONMENT === 'production'
+      ? [purgecss]
+      : []
+  ]
+}
 ```
\ No newline at end of file
diff --git a/hugolib/resource_chain_test.go b/hugolib/resource_chain_test.go
index 9590fc5de..71f57f699 100644
--- a/hugolib/resource_chain_test.go
+++ b/hugolib/resource_chain_test.go
@@ -16,7 +16,10 @@ package hugolib
 import (
 	"io"
 	"os"
+	"os/exec"
 	"path/filepath"
+	"runtime"
+	"strings"
 	"testing"
 
 	"github.com/gohugoio/hugo/htesting"
@@ -694,3 +697,122 @@ Hello2: Bonjour
 `)
 
 }
+
+func TestResourceChainPostCSS(t *testing.T) {
+	if !isCI() {
+		t.Skip("skip (relative) long running modules test when running locally")
+	}
+
+	if runtime.GOOS == "windows" {
+		// TODO(bep)
+		t.Skip("skip npm test on Windows")
+	}
+
+	wd, _ := os.Getwd()
+	defer func() {
+		os.Chdir(wd)
+	}()
+
+	c := qt.New(t)
+
+	packageJSON := `{
+  "scripts": {},
+  "dependencies": {
+    "tailwindcss": "^1.2"
+  },
+  "devDependencies": {
+    "postcss-cli": "^7.1.0"
+  }
+}
+`
+
+	postcssConfig := `
+console.error("Hugo Environment:", process.env.HUGO_ENVIRONMENT );
+
+module.exports = {
+  plugins: [
+    require('tailwindcss')
+  ]
+}
+`
+
+	tailwindCss := `
+@tailwind base;
+@tailwind components;
+@tailwind utilities;
+
+@import "components/all.css";
+
+h1 {
+    @apply text-2xl font-bold;
+}
+  
+`
+
+	workDir, clean, err := htesting.CreateTempDir(hugofs.Os, "hugo-test-postcss")
+	c.Assert(err, qt.IsNil)
+	defer clean()
+
+	v := viper.New()
+	v.Set("workingDir", workDir)
+	v.Set("disableKinds", []string{"taxonomyTerm", "taxonomy", "page"})
+	b := newTestSitesBuilder(t).WithLogger(loggers.NewWarningLogger())
+	// Need to use OS fs for this.
+	b.Fs = hugofs.NewDefault(v)
+	b.WithWorkingDir(workDir)
+	b.WithViper(v)
+
+	cssDir := filepath.Join(workDir, "assets", "css", "components")
+	b.Assert(os.MkdirAll(cssDir, 0777), qt.IsNil)
+
+	b.WithContent("p1.md", "")
+	b.WithTemplates("index.html", `
+{{ $options := dict "inlineImports" true }}
+{{ $styles := resources.Get "css/styles.css" | resources.PostCSS $options }}
+Styles RelPermalink: {{ $styles.RelPermalink }}
+{{ $cssContent := $styles.Content }}
+Styles Content: Len: {{ len $styles.Content }}|
+
+`)
+	b.WithSourceFile("assets/css/styles.css", tailwindCss)
+	b.WithSourceFile("assets/css/components/all.css", `
+@import "a.css";
+@import "b.css";
+`, "assets/css/components/a.css", `
+class-in-a {
+	color: blue;
+}
+`, "assets/css/components/b.css", `
+@import "a.css";
+
+class-in-b {
+	color: blue;
+}
+`)
+
+	b.WithSourceFile("package.json", packageJSON)
+	b.WithSourceFile("postcss.config.js", postcssConfig)
+
+	b.Assert(os.Chdir(workDir), qt.IsNil)
+	_, err = exec.Command("npm", "install").CombinedOutput()
+	b.Assert(err, qt.IsNil)
+
+	out, _ := captureStderr(func() error {
+		b.Build(BuildCfg{})
+		return nil
+	})
+
+	// Make sure Node sees this.
+	b.Assert(out, qt.Contains, "Hugo Environment: production")
+
+	b.AssertFileContent("public/index.html", `
+Styles RelPermalink: /css/styles.css
+Styles Content: Len: 770878|
+`)
+
+	content := b.FileContent("public/css/styles.css")
+
+	b.Assert(strings.Contains(content, "class-in-a"), qt.Equals, true)
+	b.Assert(strings.Contains(content, "class-in-b"), qt.Equals, true)
+
+}
diff --git a/hugolib/testhelpers_test.go b/hugolib/testhelpers_test.go
index ac6fe4348..fe6f3b7e3 100644
--- a/hugolib/testhelpers_test.go
+++ b/hugolib/testhelpers_test.go
@@ -1039,3 +1039,18 @@ func skipSymlink(t *testing.T) {
 	}
 
 }
+
+func captureStderr(f func() error) (string, error) {
+	old := os.Stderr
+	r, w, _ := os.Pipe()
+	os.Stderr = w
+
+	err := f()
+
+	w.Close()
+	os.Stderr = old
+
+	var buf bytes.Buffer
+	io.Copy(&buf, r)
+	return buf.String(), err
+}
diff --git a/resources/resource_transformers/postcss/postcss.go b/resources/resource_transformers/postcss/postcss.go
index f262a5c91..5085670c7 100644
--- a/resources/resource_transformers/postcss/postcss.go
+++ b/resources/resource_transformers/postcss/postcss.go
@@ -14,8 +14,18 @@
 package postcss
 
 import (
+	"crypto/sha256"
+	"encoding/hex"
 	"io"
+	"io/ioutil"
+	"path"
 	"path/filepath"
+	"regexp"
+	"strings"
+
+	"github.com/gohugoio/hugo/config"
+
+	"github.com/spf13/afero"
 
 	"github.com/gohugoio/hugo/resources/internal"
 	"github.com/spf13/cast"
@@ -33,6 +43,8 @@ import (
 	"github.com/gohugoio/hugo/resources/resource"
 )
 
+const importIdentifier = "@import"
+
 // Some of the options from https://github.com/postcss/postcss-cli
 type Options struct {
 
@@ -41,6 +53,14 @@ type Options struct {
 
 	NoMap bool // Disable the default inline sourcemaps
 
+	// Enable inlining of @import statements.
+	// Does so recursively, but currently once only per file;
+	// that is, it's not possible to import the same file in
+	// different scopes (root, media query...)
+	// Note that this import routine does not care about the CSS spec,
+	// so you can have @import anywhere in the file.
+	InlineImports bool
+
 	// Options for when not using a config file
 	Use         string // List of postcss plugins to use
 	Parser      string //  Custom postcss parser
@@ -168,15 +188,28 @@ func (t *postcssTransformation) Transform(ctx *resources.ResourceTransformationC
 
 	cmd.Stdout = ctx.To
 	cmd.Stderr = os.Stderr
+	// TODO(bep) somehow generalize this to other external helpers that may need this.
+	env := os.Environ()
+	config.SetEnvVars(&env, "HUGO_ENVIRONMENT", t.rs.Cfg.GetString("environment"))
+	cmd.Env = env
 
 	stdin, err := cmd.StdinPipe()
 	if err != nil {
 		return err
 	}
 
+	src := ctx.From
+	if t.options.InlineImports {
+		var err error
+		src, err = t.inlineImports(ctx)
+		if err != nil {
+			return err
+		}
+	}
+
 	go func() {
 		defer stdin.Close()
-		io.Copy(stdin, ctx.From)
+		io.Copy(stdin, src)
 	}()
 
 	err = cmd.Run()
@@ -187,7 +220,108 @@ func (t *postcssTransformation) Transform(ctx *resources.ResourceTransformationC
 	return nil
 }
 
+func (t *postcssTransformation) inlineImports(ctx *resources.ResourceTransformationCtx) (io.Reader, error) {
+
+	const importIdentifier = "@import"
+
+	// Set of content hashes.
+	contentSeen := make(map[string]bool)
+
+	content, err := ioutil.ReadAll(ctx.From)
+	if err != nil {
+		return nil, err
+	}
+
+	contents := string(content)
+
+	newContent, err := t.importRecursive(contentSeen, contents, ctx.InPath)
+	if err != nil {
+		return nil, err
+	}
+
+	return strings.NewReader(newContent), nil
+
+}
+
+func (t *postcssTransformation) importRecursive(
+	contentSeen map[string]bool,
+	content string,
+	inPath string) (string, error) {
+
+	basePath := path.Dir(inPath)
+
+	var replacements []string
+	lines := strings.Split(content, "\n")
+
+	for _, line := range lines {
+		line = strings.TrimSpace(line)
+		if shouldImport(line) {
+			path := strings.Trim(strings.TrimPrefix(line, importIdentifier), " \"';")
+			filename := filepath.Join(basePath, path)
+			importContent, hash := t.contentHash(filename)
+			if importContent == nil {
+				t.rs.Logger.WARN.Printf("postcss: Failed to resolve CSS @import in %q for path %q", inPath, filename)
+				continue
+			}
+
+			if contentSeen[hash] {
+				// Just replace the line with an empty string.
+				replacements = append(replacements, []string{line, ""}...)
+				continue
+			}
+
+			contentSeen[hash] = true
+
+			// Handle recursive imports.
+			nested, err := t.importRecursive(contentSeen, string(importContent), filepath.ToSlash(filename))
+			if err != nil {
+				return "", err
+			}
+			importContent = []byte(nested)
+
+			replacements = append(replacements, []string{line, string(importContent)}...)
+		}
+	}
+
+	if len(replacements) > 0 {
+		repl := strings.NewReplacer(replacements...)
+		content = repl.Replace(content)
+	}
+
+	return content, nil
+}
+
+func (t *postcssTransformation) contentHash(filename string) ([]byte, string) {
+	b, err := afero.ReadFile(t.rs.Assets.Fs, filename)
+	if err != nil {
+		return nil, ""
+	}
+	h := sha256.New()
+	h.Write(b)
+	return b, hex.EncodeToString(h.Sum(nil))
+}
+
 // Process transforms the given Resource with the PostCSS processor.
 func (c *Client) Process(res resources.ResourceTransformer, options Options) (resource.Resource, error) {
 	return res.Transform(&postcssTransformation{rs: c.rs, options: options})
 }
+
+var shouldImportRe = regexp.MustCompile(`^@import ["'].*["'];?\s*(/\*.*\*/)?$`)
+
+// See https://www.w3schools.com/cssref/pr_import_rule.asp
+// We currently only support simple file imports, no urls, no media queries.
+// So this is OK:
+//     @import "navigation.css";
+// This is not:
+//     @import url("navigation.css");
+//     @import "mobstyle.css" screen and (max-width: 768px);
+func shouldImport(s string) bool {
+	if !strings.HasPrefix(s, importIdentifier) {
+		return false
+	}
+	if strings.Contains(s, "url(") {
+		return false
+	}
+
+	return shouldImportRe.MatchString(s)
+}
diff --git a/resources/resource_transformers/postcss/postcss_test.go b/resources/resource_transformers/postcss/postcss_test.go
index 39936d6b4..02c0ecb55 100644
--- a/resources/resource_transformers/postcss/postcss_test.go
+++ b/resources/resource_transformers/postcss/postcss_test.go
@@ -37,3 +37,21 @@ func TestDecodeOptions(t *testing.T) {
 	c.Assert(opts2.NoMap, qt.Equals, true)
 
 }
+
+func TestShouldImport(t *testing.T) {
+	c := qt.New(t)
+
+	for _, test := range []struct {
+		input  string
+		expect bool
+	}{
+		{input: `@import "navigation.css";`, expect: true},
+		{input: `@import "navigation.css"; /* Using a string */`, expect: true},
+		{input: `@import "navigation.css"`, expect: true},
+		{input: `@import 'navigation.css';`, expect: true},
+		{input: `@import url("navigation.css");`, expect: false},
+		{input: `@import url('https://fonts.googleapis.com/css?family=Open+Sans:400,400i,800,800i&display=swap');`, expect: false},
+	} {
+		c.Assert(shouldImport(test.input), qt.Equals, test.expect)
+	}
+}