Add config extends and entry point exclusion

Profiles may inherit from another config file (extends: <path>): the
first profile of the referenced file is merged underneath (scalars from
the overlay win, slices concatenate base-first and de-duplicate, chains
resolve recursively, cycles are detected).

esbuild.excludeEntryPoints removes merged entry points by glob (** spans
path separators, * stays within a segment), applied after path
resolution so patterns and entries match in the same shape.

Lets product editions/flavors (e.g. the wmd4x Range Trader Pro edition)
build only their own entry set on top of a shared, merge-clean base
config. Includes unit tests and template docs.

config.go

@@ -38,20 +38,22 @@ func cfgToESBuildCfg(cfg options) api.BuildOptions {
 }
 
 type options struct {
+	Extends string `yaml:"extends"` // inherit from the first profile of the referenced config file
 	ESBuild struct {
-		EntryPoints      []string `yaml:"entryPoints"`
-		Outdir           string   `yaml:"outdir"`
-		Outbase          string   `yaml:"outbase"`
-		Outfile          string   `yaml:"outfile"`
-		Sourcemap        int      `yaml:"sourcemap"`
-		Format           int      `yaml:"format"`
-		Splitting        bool     `yaml:"splitting"`
-		Platform         int      `yaml:"platform"`
-		Bundle           bool     `yaml:"bundle"`
-		Write            bool     `yaml:"write"`
-		LogLevel         int      `yaml:"logLevel"`
-		Target           int      `yaml:"target"`
-		PurgeBeforeBuild bool     `yaml:"purgeBeforeBuild"`
+		EntryPoints        []string `yaml:"entryPoints"`
+		ExcludeEntryPoints []string `yaml:"excludeEntryPoints"`
+		Outdir             string   `yaml:"outdir"`
+		Outbase            string   `yaml:"outbase"`
+		Outfile            string   `yaml:"outfile"`
+		Sourcemap          int      `yaml:"sourcemap"`
+		Format             int      `yaml:"format"`
+		Splitting          bool     `yaml:"splitting"`
+		Platform           int      `yaml:"platform"`
+		Bundle             bool     `yaml:"bundle"`
+		Write              bool     `yaml:"write"`
+		LogLevel           int      `yaml:"logLevel"`
+		Target             int      `yaml:"target"`
+		PurgeBeforeBuild   bool     `yaml:"purgeBeforeBuild"`
 	} `yaml:"esbuild"`
 	Watch struct {
 		Paths            []string `yaml:"paths"`
@@ -119,6 +121,38 @@ func readCfg(cfgPath string) []options {
 		cfgPath = yamlPath
 	}
 
+	profiles := readCfgFile(cfgPath, map[string]bool{})
+
+	// Path resolution and entry point filtering run once, after all extends
+	// chains are merged, so de-duplication compares like with like and
+	// patterns match the same shape as the entries.
+	for i := range profiles {
+		processPaths(&profiles[i])
+		filterEntryPoints(&profiles[i])
+	}
+
+	return profiles
+}
+
+// readCfgFile loads a config file and resolves `extends` chains. A profile
+// may declare `extends: <path>`; the first profile of the referenced file is
+// merged underneath it (scalars: overlay wins when set, slices: concatenated
+// base-first and de-duplicated). Chains are resolved recursively; visiting
+// guards against inheritance cycles.
+func readCfgFile(cfgPath string, visiting map[string]bool) []options {
+	absPath, err := filepath.Abs(cfgPath)
+	if err != nil {
+		fmt.Printf("%+v\n", err)
+		os.Exit(1)
+	}
+
+	if visiting[absPath] {
+		fmt.Printf("extends cycle detected at %s\n", absPath)
+		os.Exit(1)
+	}
+	visiting[absPath] = true
+	defer delete(visiting, absPath)
+
 	cfgContent, err := os.ReadFile(cfgPath)
 
 	if err != nil {
@@ -140,9 +174,27 @@ func readCfg(cfgPath string) []options {
 		optsSetups = append(optsSetups, opt)
 	}
 
-	// Process all paths in each options setup
+	cfgDir := filepath.Dir(cfgPath)
+
 	for i := range optsSetups {
-		processPaths(&optsSetups[i])
+		base := strings.TrimSpace(optsSetups[i].Extends)
+
+		if base == "" {
+			continue
+		}
+
+		if !filepath.IsAbs(base) {
+			base = filepath.Join(cfgDir, base)
+		}
+
+		baseProfiles := readCfgFile(base, visiting)
+
+		if len(baseProfiles) == 0 {
+			fmt.Printf("extends target %s contains no profiles\n", base)
+			os.Exit(1)
+		}
+
+		optsSetups[i] = mergeOptions(baseProfiles[0], optsSetups[i])
 	}
 
 	return optsSetups
@@ -178,6 +230,10 @@ func processPaths(opts *options) {
 	for i, entry := range opts.ESBuild.EntryPoints {
 		opts.ESBuild.EntryPoints[i] = fsutils.ResolvePath(entry)
 	}
+
+	for i, entry := range opts.ESBuild.ExcludeEntryPoints {
+		opts.ESBuild.ExcludeEntryPoints[i] = fsutils.ResolvePath(entry)
+	}
 	opts.ESBuild.Outdir = fsutils.ResolvePath(opts.ESBuild.Outdir)
 	opts.ESBuild.Outfile = fsutils.ResolvePath(opts.ESBuild.Outfile)