Add segments config + --renderSegments flag

Named segments can be defined in `hugo.toml`.

* Eeach segment consists of zero or more `exclude` filters and zero or more `include` filters.
* Eeach filter consists of one or more field Glob matchers.
* Eeach filter in a section (`exclude` or `include`) is ORed together, each matcher in a filter is ANDed together.

The current list of fields that can be filtered are:

* path as defined in https://gohugo.io/methods/page/path/
* kind
* lang
* output (output format, e.g. html).

It is recommended to put coarse grained filters (e.g. for language and output format) in the excludes section, e.g.:

```toml
[segments.segment1]
  [[segments.segment1.excludes]]
    lang = "n*"
  [[segments.segment1.excludes]]
    no     = "en"
    output = "rss"
  [[segments.segment1.includes]]
    term = "{home,term,taxonomy}"
  [[segments.segment1.includes]]
    path = "{/docs,/docs/**}"
```

By default, Hugo will render all segments, but you can enable filters by setting the `renderSegments` option or `--renderSegments` flag, e.g:

```
hugo --renderSegments segment1,segment2
```

For segment `segment1` in the configuration above, this will:

* Skip rendering of all languages matching `n*`, e.g. `no`.
* Skip rendering of the output format `rss` for the `en` language.
* It will render all pages of kind `home`, `term` or `taxonomy`
* It will render the `/docs` section and all pages below.

Fixes #10106

2 files changed, 20 insertions, 0 deletions

diff --git a/config/allconfig/allconfig.go b/config/allconfig/allconfig.go
index 3a7908d55..f0e72dabc 100644
--- a/config/allconfig/allconfig.go
+++ b/config/allconfig/allconfig.go
@@ -39,6 +39,7 @@ import (
 	"github.com/gohugoio/hugo/config/services"
 	"github.com/gohugoio/hugo/deploy/deployconfig"
 	"github.com/gohugoio/hugo/helpers"
+	"github.com/gohugoio/hugo/hugolib/segments"
 	"github.com/gohugoio/hugo/langs"
 	"github.com/gohugoio/hugo/markup/markup_config"
 	"github.com/gohugoio/hugo/media"
@@ -139,6 +140,9 @@ type Config struct {
 	// a slice of page matcher and params to apply to those pages.
 	Cascade *config.ConfigNamespace[[]page.PageMatcherParamsConfig, map[page.PageMatcher]maps.Params] `mapstructure:"-"`
 
+	// The segments defines segments for the site. Used for partial/segmented builds.
+	Segments *config.ConfigNamespace[map[string]segments.SegmentConfig, segments.Segments] `mapstructure:"-"`
+
 	// Menu configuration.
 	// <docsmeta>{"refs": ["config:languages:menus"] }</docsmeta>
 	Menus *config.ConfigNamespace[map[string]navigation.MenuConfig, navigation.Menus] `mapstructure:"-"`
@@ -366,6 +370,7 @@ func (c *Config) CompileConfig(logger loggers.Logger) error {
 		CreateTitle:       helpers.GetTitleFunc(c.TitleCaseStyle),
 		IsUglyURLSection:  isUglyURL,
 		IgnoreFile:        ignoreFile,
+		SegmentFilter:     c.Segments.Config.Get(func(s string) { logger.Warnf("Render segment %q not found in configuration", s) }, c.RootConfig.RenderSegments...),
 		MainSections:      c.MainSections,
 		Clock:             clock,
 		transientErr:      transientErr,
@@ -402,6 +407,7 @@ type ConfigCompiled struct {
 	CreateTitle       func(s string) string
 	IsUglyURLSection  func(section string) bool
 	IgnoreFile        func(filename string) bool
+	SegmentFilter     segments.SegmentFilter
 	MainSections      []string
 	Clock             time.Time
 
@@ -474,6 +480,10 @@ type RootConfig struct {
 	// A list of languages to disable.
 	DisableLanguages []string
 
+	// The named segments to render.
+	// This needs to match the name of the segment in the segments configuration.
+	RenderSegments []string
+
 	// Disable the injection of the Hugo generator tag on the home page.
 	DisableHugoGeneratorInject bool
 
diff --git a/config/allconfig/alldecoders.go b/config/allconfig/alldecoders.go
index 5d31d5d35..7d968e4ad 100644
--- a/config/allconfig/alldecoders.go
+++ b/config/allconfig/alldecoders.go
@@ -25,11 +25,13 @@ import (
 	"github.com/gohugoio/hugo/config/security"
 	"github.com/gohugoio/hugo/config/services"
 	"github.com/gohugoio/hugo/deploy/deployconfig"
+	"github.com/gohugoio/hugo/hugolib/segments"
 	"github.com/gohugoio/hugo/langs"
 	"github.com/gohugoio/hugo/markup/markup_config"
 	"github.com/gohugoio/hugo/media"
 	"github.com/gohugoio/hugo/minifiers"
 	"github.com/gohugoio/hugo/modules"
+
 	"github.com/gohugoio/hugo/navigation"
 	"github.com/gohugoio/hugo/output"
 	"github.com/gohugoio/hugo/related"
@@ -120,6 +122,14 @@ var allDecoderSetups = map[string]decodeWeight{
 			return err
 		},
 	},
+	"segments": {
+		key: "segments",
+		decode: func(d decodeWeight, p decodeConfig) error {
+			var err error
+			p.c.Segments, err = segments.DecodeSegments(p.p.GetStringMap(d.key))
+			return err
+		},
+	},
 	"server": {
 		key: "server",
 		decode: func(d decodeWeight, p decodeConfig) error {