Lesson 15 · Ignoring by basename - Build a Glob and Gitignore Matcher

Ignoring by basename

The core question is finally answerable: does a rule-set ignore a path? A plain pattern with no slash floats - it matches the file's basename at any depth. Today Ignored answers for these floating patterns.

The goal

Make a slash-free pattern match a path's basename at any depth.

Start here - the target

TO DO

Scenario: A floating pattern matches the basename anywhere

Givena rule-set with a slash-free pattern

WhenIgnored is asked about a path

Thena floating pattern matches the basename at any depth: Compile("*.log").Ignored("a.log", false) is true and Compile("*.log").Ignored("dir/a.log", false) is true

Andit matches the basename only, not other segments: Compile("*.log").Ignored("a.txt", false) is false and Compile("foo").Ignored("x/y/foo", false) is true

Background

Now the payoff: Ignored(path, isDir) reports whether the rule-set ignores a given path. The simplest and most common gitignore rule is a pattern with no slash in it, like *.log or build. Such a pattern floats: it matches the path’s basename - the last segment - no matter how deep the path is. So *.log ignores a.log and dir/a.log and x/y/z.log alike, because in each the final segment ends in .log.

Because a floating pattern only ever looks at one segment, you match it with matchSegment - the single-segment engine from the first two chapters, reused untouched. Pull the basename off the path and test each rule against it; ignored if any rule matches. The isDir argument is here from the start because a coming lesson needs it, but today it is unused. This is the whole engine in miniature; anchoring, directories, and negation each refine how a rule matches from here.

Make it work

func (g *Gitignore) Ignored(path string, isDir bool) bool {
  base := path
  if i := strings.LastIndex(path, "/"); i >= 0 {
    base = path[i+1:]         // the final path segment
  }
  for _, r := range g.rules {
    if matchSegment(r.Pattern, base) { return true }
  }
  return false
}

CheckpointDONE

A floating pattern ignores a path by matching its basename. Commit and stop here.