go-git-gitignore: copy matcher.go, pattern.go from go-git/plumbing/format/gitignore

Files copied from
https://github.com/go-git/go-git/tree/7bc22667c9e181cc1361eccec77f1a237abee860/plumbing/format/gitignore .

Importing all of go-git pulls in a metric ton of dependencies,
so I have decided to only copy the two files we need.

https://github.com/rfjakob/gocryptfs/issues/927

4 files changed, 399 insertions, 0 deletions

diff --git a/internal/go-git-gitignore/LICENSE b/internal/go-git-gitignore/LICENSE
new file mode 100644
index 0000000..8aa3d85
--- /dev/null
+++ b/internal/go-git-gitignore/LICENSE
@@ -0,0 +1,201 @@
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diff --git a/internal/go-git-gitignore/README.md b/internal/go-git-gitignore/README.md
new file mode 100644
index 0000000..fff42bf
--- /dev/null
+++ b/internal/go-git-gitignore/README.md
@@ -0,0 +1,9 @@
+Imported from
+https://github.com/go-git/go-git - A highly extensible Git implementation in pure Go.
+using the commands below:
+
+```
+curl --remote-name-all https://raw.githubusercontent.com/go-git/go-git/refs/heads/main/LICENSE \
+ https://raw.githubusercontent.com/go-git/go-git/refs/heads/main/plumbing/format/gitignore/matcher.go \
+ https://raw.githubusercontent.com/go-git/go-git/refs/heads/main/plumbing/format/gitignore/pattern.go
+```
diff --git a/internal/go-git-gitignore/matcher.go b/internal/go-git-gitignore/matcher.go
new file mode 100644
index 0000000..bd1e9e2
--- /dev/null
+++ b/internal/go-git-gitignore/matcher.go
@@ -0,0 +1,30 @@
+package gitignore
+
+// Matcher defines a global multi-pattern matcher for gitignore patterns
+type Matcher interface {
+	// Match matches patterns in the order of priorities. As soon as an inclusion or
+	// exclusion is found, not further matching is performed.
+	Match(path []string, isDir bool) bool
+}
+
+// NewMatcher constructs a new global matcher. Patterns must be given in the order of
+// increasing priority. That is most generic settings files first, then the content of
+// the repo .gitignore, then content of .gitignore down the path or the repo and then
+// the content command line arguments.
+func NewMatcher(ps []Pattern) Matcher {
+	return &matcher{ps}
+}
+
+type matcher struct {
+	patterns []Pattern
+}
+
+func (m *matcher) Match(path []string, isDir bool) bool {
+	n := len(m.patterns)
+	for i := n - 1; i >= 0; i-- {
+		if match := m.patterns[i].Match(path, isDir); match > NoMatch {
+			return match == Exclude
+		}
+	}
+	return false
+}
diff --git a/internal/go-git-gitignore/pattern.go b/internal/go-git-gitignore/pattern.go
new file mode 100644
index 0000000..c80e841
--- /dev/null
+++ b/internal/go-git-gitignore/pattern.go
@@ -0,0 +1,159 @@
+package gitignore
+
+import (
+	"path/filepath"
+	"strings"
+)
+
+// MatchResult defines outcomes of a match, no match, exclusion or inclusion.
+type MatchResult int
+
+const (
+	// NoMatch defines the no match outcome of a match check
+	NoMatch MatchResult = iota
+	// Exclude defines an exclusion of a file as a result of a match check
+	Exclude
+	// Include defines an explicit inclusion of a file as a result of a match check
+	Include
+)
+
+const (
+	inclusionPrefix = "!"
+	zeroToManyDirs  = "**"
+	patternDirSep   = "/"
+)
+
+// Pattern defines a single gitignore pattern.
+type Pattern interface {
+	// Match matches the given path to the pattern.
+	Match(path []string, isDir bool) MatchResult
+}
+
+type pattern struct {
+	domain    []string
+	pattern   []string
+	inclusion bool
+	dirOnly   bool
+	isGlob    bool
+}
+
+// ParsePattern parses a gitignore pattern string into the Pattern structure.
+func ParsePattern(p string, domain []string) Pattern {
+	// storing domain, copy it to ensure it isn't changed externally
+	domain = append([]string(nil), domain...)
+	res := pattern{domain: domain}
+
+	if strings.HasPrefix(p, inclusionPrefix) {
+		res.inclusion = true
+		p = p[1:]
+	}
+
+	if !strings.HasSuffix(p, "\\ ") {
+		p = strings.TrimRight(p, " ")
+	}
+
+	if strings.HasSuffix(p, patternDirSep) {
+		res.dirOnly = true
+		p = p[:len(p)-1]
+	}
+
+	if strings.Contains(p, patternDirSep) {
+		res.isGlob = true
+	}
+
+	res.pattern = strings.Split(p, patternDirSep)
+	return &res
+}
+
+func (p *pattern) Match(path []string, isDir bool) MatchResult {
+	if len(path) <= len(p.domain) {
+		return NoMatch
+	}
+	for i, e := range p.domain {
+		if path[i] != e {
+			return NoMatch
+		}
+	}
+
+	path = path[len(p.domain):]
+	if p.isGlob && !p.globMatch(path, isDir) {
+		return NoMatch
+	} else if !p.isGlob && !p.simpleNameMatch(path, isDir) {
+		return NoMatch
+	}
+
+	if p.inclusion {
+		return Include
+	} else {
+		return Exclude
+	}
+}
+
+func (p *pattern) simpleNameMatch(path []string, isDir bool) bool {
+	for i, name := range path {
+		if match, err := filepath.Match(p.pattern[0], name); err != nil {
+			return false
+		} else if !match {
+			continue
+		}
+		if p.dirOnly && !isDir && i == len(path)-1 {
+			return false
+		}
+		return true
+	}
+	return false
+}
+
+func (p *pattern) globMatch(path []string, isDir bool) bool {
+	matched := false
+	canTraverse := false
+	for i, pattern := range p.pattern {
+		if pattern == "" {
+			canTraverse = false
+			continue
+		}
+		if pattern == zeroToManyDirs {
+			if i == len(p.pattern)-1 {
+				break
+			}
+			canTraverse = true
+			continue
+		}
+		if strings.Contains(pattern, zeroToManyDirs) {
+			return false
+		}
+		if len(path) == 0 {
+			return false
+		}
+		if canTraverse {
+			canTraverse = false
+			for len(path) > 0 {
+				e := path[0]
+				path = path[1:]
+				if match, err := filepath.Match(pattern, e); err != nil {
+					return false
+				} else if match {
+					matched = true
+					break
+				} else if len(path) == 0 {
+					// if nothing left then fail
+					matched = false
+				}
+			}
+		} else {
+			if match, err := filepath.Match(pattern, path[0]); err != nil || !match {
+				return false
+			}
+			matched = true
+			path = path[1:]
+			// files matching dir globs, don't match
+			if len(path) == 0 && i < len(p.pattern)-1 {
+				matched = false
+			}
+		}
+	}
+	if matched && p.dirOnly && !isDir && len(path) == 0 {
+		matched = false
+	}
+	return matched
+}