hugofs: Make node_modules a "special case" mount

For this and similar mounts in a theme:

```toml
[[module.mounts]]
source = 'node_modules/bootstrap'
target = 'assets/vendor/bootstrap'
```

We first check the theme itself, then the project root.

For backwards compatibility, we also make any `../../node_modules/...` `source` paths into `node_modules/...` paths when defined in themes/modules.

Fixes #14089

hugofs/hugofs_integration_test.go

@@ -14,6 +14,7 @@
 package hugofs_test
 
 import (
+	"strings"
 	"testing"
 
 	qt "github.com/frankban/quicktest"
@@ -44,3 +45,42 @@ All.
 	b.Assert(err, qt.IsNotNil)
 	b.Assert(err.Error(), qt.Contains, "mount source must be a local path for modules/themes")
 }
+
+// Issue 14089.
+func TestMountNodeMoudulesFromTheme(t *testing.T) {
+	filesTemplate := `
+-- hugo.toml --
+disableKinds = ["taxonomy", "term", "rss"]
+theme = "mytheme"
+-- node_modules/bootstrap/foo.txt --
+foo project.
+-- layouts/all.html --
+{{ $foo := resources.Get "vendor/bootstrap/foo.txt" }}
+Foo: {{ with $foo }}{{ .Content }}{{ else }}Fail{{ end }}
+-- themes/mytheme/hugo.toml --
+[[module.mounts]]
+source = 'NODE_MODULES_SOURCE' # tries first in theme, then in project root
+target = 'assets/vendor/bootstrap'
+
+`
+	runFiles := func(files string) *hugolib.IntegrationTestBuilder {
+		return hugolib.Test(t, files, hugolib.TestOptOsFs())
+	}
+	files := strings.ReplaceAll(filesTemplate, "NODE_MODULES_SOURCE", "node_modules/bootstrap")
+	b := runFiles(files)
+	b.AssertFileContent("public/index.html", "Foo: foo project.")
+
+	// This is for backwards compatibility. ../../node_modules/bootstrap works exactly the same as node_modules/bootstrap.
+	files = strings.ReplaceAll(filesTemplate, "NODE_MODULES_SOURCE", "../../node_modules/bootstrap")
+	b = runFiles(files)
+	b.AssertFileContent("public/index.html", "Foo: foo project.")
+
+	files = strings.ReplaceAll(filesTemplate, "NODE_MODULES_SOURCE", "node_modules/bootstrap")
+	files += `
+-- themes/mytheme/node_modules/bootstrap/foo.txt --
+foo theme.
+`
+
+	b = runFiles(files)
+	b.AssertFileContent("public/index.html", "Foo: foo theme.")
+}

modules/collect.go

@@ -695,6 +695,19 @@ func (c *collector) mountCommonJSConfig(owner *moduleAdapter, mounts []Mount) ([
 	return mounts, nil
 }
 
+func (c *collector) nodeModulesRoot(s string) string {
+	s = filepath.ToSlash(s)
+	if strings.HasPrefix(s, "node_modules/") {
+		return s
+	}
+	if strings.HasPrefix(s, "../../node_modules/") {
+		// See #14083. This was a common construct to mount node_modules from the project root.
+		// This started failing in v0.152.0 when we tightened the validation.
+		return strings.TrimPrefix(s, "../../")
+	}
+	return ""
+}
+
 func (c *collector) normalizeMounts(owner *moduleAdapter, mounts []Mount) ([]Mount, error) {
 	var out []Mount
 	dir := owner.Dir()
@@ -706,6 +719,17 @@ func (c *collector) normalizeMounts(owner *moduleAdapter, mounts []Mount) ([]Mou
 			return nil, errors.New(errMsg + ": both source and target must be set")
 		}
 
+		// Special case for node_modules imports in themes/modules.
+		// See #14089.
+		var isModuleNodeModulesImport bool
+		if !owner.projectMod {
+			nodeModulesImportSource := c.nodeModulesRoot(mnt.Source)
+			if nodeModulesImportSource != "" {
+				isModuleNodeModulesImport = true
+				mnt.Source = nodeModulesImportSource
+			}
+		}
+
 		mnt.Source = filepath.Clean(mnt.Source)
 		mnt.Target = filepath.Clean(mnt.Target)
 		var sourceDir string
@@ -741,9 +765,18 @@ func (c *collector) normalizeMounts(owner *moduleAdapter, mounts []Mount) ([]Mou
 				}
 				f.Close()
 			} else {
-				// TODO(bep) commenting out for now, as this will create to much noise.
-				// c.logger.Warnf("module %q: mount source %q does not exist", owner.Path(), sourceDir)
-				continue
+				if isModuleNodeModulesImport {
+					// A module imported a path inside node_modules, but it didn't exist.
+					// Make this a special case and also try relative to the project root.
+					sourceDir = filepath.Join(c.ccfg.WorkingDir, mnt.Source)
+					_, err := c.fs.Stat(sourceDir)
+					if err != nil {
+						continue
+					}
+					mnt.Source = sourceDir
+				} else {
+					continue
+				}
 			}
 		}