i/p/patterns: disallow /./ and /../ in path patterns

interfaces/prompting/patterns/patterns_test.go

@@ -133,6 +133,12 @@ func (s *patternsSuite) TestParsePathPatternHappy(c *C) {
 		"/foo/{a,b}{c,d}{e,f}{g,h,i,j,k}{l,m,n,o,p}{q,r,s,t,u},1,2,3", // expands to 1000, with commas outside groups
 		"/" + strings.Repeat("{a,", 999) + "a" + strings.Repeat("}", 999),
 		"/" + strings.Repeat("{", 999) + "a" + strings.Repeat(",a}", 999),
+		"/foo/.../bar",
+		"/foo/...",
+		"/foo/.{bar,baz}",
+		"/foo/..{bar,baz}",
+		"/foo/{bar,baz}.",
+		"/foo/{bar,baz}..",
 	} {
 		_, err := patterns.ParsePathPattern(pattern)
 		c.Check(err, IsNil, Commentf("valid path pattern %q was incorrectly not allowed", pattern))
@@ -152,6 +158,22 @@ func (s *patternsSuite) TestParsePathPatternUnhappy(c *C) {
 			`file.txt`,
 			`invalid path pattern: pattern must start with '/': "file.txt"`,
 		},
+		{
+			`/foo/./bar`,
+			`invalid path pattern: pattern cannot contain '/./' or '/../': .*`,
+		},
+		{
+			`/foo/../bar`,
+			`invalid path pattern: pattern cannot contain '/./' or '/../': .*`,
+		},
+		{
+			`/foo/.`,
+			`invalid path pattern: pattern cannot contain '/./' or '/../': .*`,
+		},
+		{
+			`/foo/..`,
+			`invalid path pattern: pattern cannot contain '/./' or '/../': .*`,
+		},
 		{
 			`{/,/foo}`,
 			`invalid path pattern: pattern must start with '/': .*`,

interfaces/prompting/patterns/scan.go

@@ -23,6 +23,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"regexp"
 	"strings"
 )
 
@@ -59,13 +60,19 @@ type token struct {
 	text  string
 }
 
+// relpathFinder matches `/./` and `/../` along with their trailing variants `/.` and `/..` in path patterns.
+var relpathFinder = regexp.MustCompile(`/\.(\.)?(/|$)`)
+
 func scan(text string) (tokens []token, err error) {
 	if len(text) == 0 {
 		return nil, errors.New("pattern has length 0")
 	}
 	if text[0] != '/' {
 		return nil, errors.New("pattern must start with '/'")
 	}
+	if relpathFinder.MatchString(text) {
+		return nil, errors.New("pattern cannot contain '/./' or '/../'")
+	}
 
 	var runes []rune
 

interfaces/prompting/patterns/scan_internal_test.go

@@ -123,6 +123,22 @@ func (s *scanSuite) TestScanUnhappy(c *C) {
 			`foo`,
 			`pattern must start with '/'`,
 		},
+		{
+			`/foo/./bar`,
+			`pattern cannot contain '/./' or '/../'`,
+		},
+		{
+			`/foo/../bar`,
+			`pattern cannot contain '/./' or '/../'`,
+		},
+		{
+			`/foo/.`,
+			`pattern cannot contain '/./' or '/../'`,
+		},
+		{
+			`/foo/..`,
+			`pattern cannot contain '/./' or '/../'`,
+		},
 		{
 			`/foo\`,
 			`trailing unescaped '\\' character`,