filter: Add BoundedRecursion method

This indicates that the filter set could be satisfied by a bounded
directory recursion.

fs/filter/filter.go

@@ -21,8 +21,9 @@ var Active = mustNewFilter(nil)
 
 // rule is one filter rule
 type rule struct {
-	Include bool
-	Regexp  *regexp.Regexp
+	Include          bool
+	Regexp           *regexp.Regexp
+	boundedRecursion bool
 }
 
 // Match returns true if rule matches path
@@ -46,13 +47,14 @@ type rules struct {
 }
 
 // add adds a rule if it doesn't exist already
-func (rs *rules) add(Include bool, re *regexp.Regexp) {
+func (rs *rules) add(Include bool, re *regexp.Regexp, boundedRecursion bool) {
 	if rs.existing == nil {
 		rs.existing = make(map[string]struct{})
 	}
 	newRule := rule{
-		Include: Include,
-		Regexp:  re,
+		Include:          Include,
+		Regexp:           re,
+		boundedRecursion: boundedRecursion,
 	}
 	newRuleString := newRule.String()
 	if _, ok := rs.existing[newRuleString]; ok {
@@ -73,6 +75,23 @@ func (rs *rules) len() int {
 	return len(rs.rules)
 }
 
+// boundedRecursion returns true if the set of filters would only
+// need bounded recursion to evaluate
+func (rs *rules) boundedRecursion() bool {
+	var (
+		excludeAll       = false
+		boundedRecursion = true
+	)
+	for _, rule := range rs.rules {
+		if rule.Include {
+			boundedRecursion = boundedRecursion && rule.boundedRecursion
+		} else if rule.Regexp.String() == `^.*$` {
+			excludeAll = true
+		}
+	}
+	return excludeAll && boundedRecursion
+}
+
 // FilesMap describes the map of files to transfer
 type FilesMap map[string]struct{}
 
@@ -232,7 +251,8 @@ func (f *Filter) addDirGlobs(Include bool, glob string) error {
 		if err != nil {
 			return err
 		}
-		f.dirRules.add(Include, dirRe)
+		boundedRecursion := globBoundedRecursion(dirGlob)
+		f.dirRules.add(Include, dirRe, boundedRecursion)
 	}
 	return nil
 }
@@ -248,8 +268,9 @@ func (f *Filter) Add(Include bool, glob string) error {
 	if err != nil {
 		return err
 	}
+	boundedRecursion := globBoundedRecursion(glob)
 	if isFileRule {
-		f.fileRules.add(Include, re)
+		f.fileRules.add(Include, re, boundedRecursion)
 		// If include rule work out what directories are needed to scan
 		// if exclude rule, we can't rule anything out
 		// Unless it is `*` which matches everything
@@ -262,7 +283,7 @@ func (f *Filter) Add(Include bool, glob string) error {
 		}
 	}
 	if isDirRule {
-		f.dirRules.add(Include, re)
+		f.dirRules.add(Include, re, boundedRecursion)
 	}
 	return nil
 }
@@ -343,6 +364,12 @@ func (f *Filter) InActive() bool {
 		len(f.Opt.ExcludeFile) == 0)
 }
 
+// BoundedRecursion returns true if the filter can be evaluated with
+// bounded recursion only.
+func (f *Filter) BoundedRecursion() bool {
+	return f.fileRules.boundedRecursion()
+}
+
 // includeRemote returns whether this remote passes the filter rules.
 func (f *Filter) includeRemote(remote string) bool {
 	for _, rule := range f.fileRules.rules {