fs: split overgrown fs.go (#5405)

Nothing is added or removed and no package is renamed by this change.
Just rearrange definitions between source files in the fs directory.

New source files:
- types.go      Filesystem types and interfaces
- features.go   Features and optional interfaces
- registry.go   Filesystem registry and backend options
- newfs.go      NewFs and its helpers
- configmap.go  Getters and Setters for ConfigMap
- pacer.go      Pacer with logging and calculator
The final fs.go contains what is left.

Also rename options.go to open_options.go
to dissociate from registry options.

fs/configmap.go

@@ -0,0 +1,128 @@
+// Getters and Setters for ConfigMap
+
+package fs
+
+import (
+	"os"
+	"strings"
+
+	"github.com/rclone/rclone/fs/config/configmap"
+)
+
+// A configmap.Getter to read from the environment RCLONE_CONFIG_backend_option_name
+type configEnvVars string
+
+// Get a config item from the environment variables if possible
+func (configName configEnvVars) Get(key string) (value string, ok bool) {
+	return os.LookupEnv(ConfigToEnv(string(configName), key))
+}
+
+// A configmap.Getter to read from the environment RCLONE_option_name
+type optionEnvVars struct {
+	fsInfo *RegInfo
+}
+
+// Get a config item from the option environment variables if possible
+func (oev optionEnvVars) Get(key string) (value string, ok bool) {
+	opt := oev.fsInfo.Options.Get(key)
+	if opt == nil {
+		return "", false
+	}
+	// For options with NoPrefix set, check without prefix too
+	if opt.NoPrefix {
+		value, ok = os.LookupEnv(OptionToEnv(key))
+		if ok {
+			return value, ok
+		}
+	}
+	return os.LookupEnv(OptionToEnv(oev.fsInfo.Prefix + "-" + key))
+}
+
+// A configmap.Getter to read either the default value or the set
+// value from the RegInfo.Options
+type regInfoValues struct {
+	fsInfo     *RegInfo
+	useDefault bool
+}
+
+// override the values in configMap with the either the flag values or
+// the default values
+func (r *regInfoValues) Get(key string) (value string, ok bool) {
+	opt := r.fsInfo.Options.Get(key)
+	if opt != nil && (r.useDefault || opt.Value != nil) {
+		return opt.String(), true
+	}
+	return "", false
+}
+
+// A configmap.Setter to read from the config file
+type setConfigFile string
+
+// Set a config item into the config file
+func (section setConfigFile) Set(key, value string) {
+	if strings.HasPrefix(string(section), ":") {
+		Logf(nil, "Can't save config %q = %q for on the fly backend %q", key, value, section)
+		return
+	}
+	Debugf(nil, "Saving config %q = %q in section %q of the config file", key, value, section)
+	err := ConfigFileSet(string(section), key, value)
+	if err != nil {
+		Errorf(nil, "Failed saving config %q = %q in section %q of the config file: %v", key, value, section, err)
+	}
+}
+
+// A configmap.Getter to read from the config file
+type getConfigFile string
+
+// Get a config item from the config file
+func (section getConfigFile) Get(key string) (value string, ok bool) {
+	value, ok = ConfigFileGet(string(section), key)
+	// Ignore empty lines in the config file
+	if value == "" {
+		ok = false
+	}
+	return value, ok
+}
+
+// ConfigMap creates a configmap.Map from the *RegInfo and the
+// configName passed in. If connectionStringConfig has any entries (it may be nil),
+// then it will be added to the lookup with the highest priority.
+//
+// If fsInfo is nil then the returned configmap.Map should only be
+// used for reading non backend specific parameters, such as "type".
+func ConfigMap(fsInfo *RegInfo, configName string, connectionStringConfig configmap.Simple) (config *configmap.Map) {
+	// Create the config
+	config = configmap.New()
+
+	// Read the config, more specific to least specific
+
+	// Config from connection string
+	if len(connectionStringConfig) > 0 {
+		config.AddGetter(connectionStringConfig, configmap.PriorityNormal)
+	}
+
+	// flag values
+	if fsInfo != nil {
+		config.AddGetter(&regInfoValues{fsInfo, false}, configmap.PriorityNormal)
+	}
+
+	// remote specific environment vars
+	config.AddGetter(configEnvVars(configName), configmap.PriorityNormal)
+
+	// backend specific environment vars
+	if fsInfo != nil {
+		config.AddGetter(optionEnvVars{fsInfo: fsInfo}, configmap.PriorityNormal)
+	}
+
+	// config file
+	config.AddGetter(getConfigFile(configName), configmap.PriorityConfig)
+
+	// default values
+	if fsInfo != nil {
+		config.AddGetter(&regInfoValues{fsInfo, true}, configmap.PriorityDefault)
+	}
+
+	// Set Config
+	config.AddSetter(setConfigFile(configName))
+	return config
+}