pattern: "**" only acts as globstar when alone as a path element

See the parent commit for a detailed explanation of the context.

Fixes #1149.

Author: mvdan

pattern/pattern.go

@@ -81,8 +81,11 @@ writeLoop:
 		switch c := pat[i]; c {
 		case '*':
 			if mode&Filenames != 0 {
+				// "**" only acts as globstar if it is alone as a path element.
+				singleBefore := i == 0 || pat[i-1] == '/'
 				if i++; i < len(pat) && pat[i] == '*' {
-					if mode&NoGlobStar != 0 {
+					singleAfter := i == len(pat)-1 || pat[i+1] == '/'
+					if mode&NoGlobStar != 0 || !singleBefore || !singleAfter {
 						buf.WriteString("[^/]*")
 					} else if i++; i < len(pat) && pat[i] == '/' {
 						buf.WriteString("(.*/|)")

pattern/pattern_test.go

@@ -37,21 +37,19 @@ var regexpTests = []struct {
 	{pat: `/**/foo`, mode: Filenames | NoGlobStar, want: `/[^/]*/foo`},
 	{pat: `/**/à`, mode: Filenames, want: `(?s)/(.*/|)à`},
 	{
-		pat: `/**foo`, mode: Filenames, want: `(?s)/.*foo`,
+		pat: `/**foo`, mode: Filenames, want: `/[^/]*foo`,
 		// These all match because without EntireString, we match substrings.
 		mustMatch: []string{"/foo", "/prefix-foo", "/foo-suffix", "/sub/foo"},
 	},
 	{
-		pat: `/**foo`, mode: Filenames | EntireString, want: `(?s)^/.*foo$`,
-		// TODO: /sub/foo should not match; see issue 1149
-		mustMatch:    []string{"/foo", "/prefix-foo", "/sub/foo"},
-		mustNotMatch: []string{"/foo-suffix"},
+		pat: `/**foo`, mode: Filenames | EntireString, want: `^/[^/]*foo$`,
+		mustMatch:    []string{"/foo", "/prefix-foo"},
+		mustNotMatch: []string{"/foo-suffix", "/sub/foo"},
 	},
 	{
-		pat: `/foo**`, mode: Filenames | EntireString, want: `(?s)^/foo.*$`,
-		// TODO: /foo/sub should not match; see issue 1149
-		mustMatch:    []string{"/foo", "/foo-suffix", "/foo/sub"},
-		mustNotMatch: []string{"/prefix-foo"},
+		pat: `/foo**`, mode: Filenames | EntireString, want: `^/foo[^/]*$`,
+		mustMatch:    []string{"/foo", "/foo-suffix"},
+		mustNotMatch: []string{"/prefix-foo", "/foo/sub"},
 	},
 	{pat: `\*`, want: `\*`},
 	{pat: `\`, wantErr: true},