Allow setting the delimiter used for setting config via OS env, e.g. HUGO_

Fixes #7829

hugolib/config.go

@@ -18,6 +18,8 @@ import (
 	"path/filepath"
 	"strings"
 
+	"github.com/gohugoio/hugo/common/types"
+
 	"github.com/gobwas/glob"
 	hglob "github.com/gohugoio/hugo/hugofs/glob"
 
@@ -166,45 +168,59 @@ func LoadConfig(d ConfigSourceDescriptor, doWithConfig ...func(cfg config.Provid
 		}
 	}
 
+	const delim = "__env__delim"
+
 	// Apply environment overrides
 	if len(d.Environ) > 0 {
-		// Extract all that start with the HUGO_ prefix
-		const hugoEnvPrefix = "HUGO_"
-		var hugoEnv []string
+		// Extract all that start with the HUGO prefix.
+		// The delimiter is the following rune, usually "_".
+		const hugoEnvPrefix = "HUGO"
+		var hugoEnv []types.KeyValueStr
 		for _, v := range d.Environ {
 			key, val := config.SplitEnvVar(v)
 			if strings.HasPrefix(key, hugoEnvPrefix) {
-				hugoEnv = append(hugoEnv, strings.ToLower(strings.TrimPrefix(key, hugoEnvPrefix)), val)
+				delimiterAndKey := strings.TrimPrefix(key, hugoEnvPrefix)
+				if len(delimiterAndKey) < 2 {
+					continue
+				}
+				// Allow delimiters to be case sensitive.
+				// It turns out there isn't that many allowed special
+				// chars in environment variables when used in Bash and similar,
+				// so variables on the form HUGOxPARAMSxFOO=bar is one option.
+				key := strings.ReplaceAll(delimiterAndKey[1:], delimiterAndKey[:1], delim)
+				key = strings.ToLower(key)
+				hugoEnv = append(hugoEnv, types.KeyValueStr{
+					Key:   key,
+					Value: val,
+				})
+
 			}
 		}
 
-		if len(hugoEnv) > 0 {
-			for i := 0; i < len(hugoEnv); i += 2 {
-				key, valStr := strings.ToLower(hugoEnv[i]), hugoEnv[i+1]
+		for _, env := range hugoEnv {
+			existing, nestedKey, owner, err := maps.GetNestedParamFn(env.Key, delim, v.Get)
+			if err != nil {
+				return v, configFiles, err
+			}
 
-				existing, nestedKey, owner, err := maps.GetNestedParamFn(key, "_", v.Get)
+			if existing != nil {
+				val, err := metadecoders.Default.UnmarshalStringTo(env.Value, existing)
 				if err != nil {
-					return v, configFiles, err
+					continue
 				}
 
-				if existing != nil {
-					val, err := metadecoders.Default.UnmarshalStringTo(valStr, existing)
-					if err != nil {
-						continue
-					}
-
-					if owner != nil {
-						owner[nestedKey] = val
-					} else {
-						v.Set(key, val)
-					}
-				} else if nestedKey != "" {
-					owner[nestedKey] = valStr
+				if owner != nil {
+					owner[nestedKey] = val
 				} else {
-					v.Set(key, valStr)
+					v.Set(env.Key, val)
 				}
+			} else if nestedKey != "" {
+				owner[nestedKey] = env.Value
+			} else {
+				v.Set(env.Key, env.Value)
 			}
 		}
+
 	}
 
 	// We made this a Glob pattern in Hugo 0.75, we don't need both.