Move `IsReadmeFile*` from `modules/markup/` to `modules/util` (#22877)

These functions don't examine contents, just filenames, so they don't
fit in well in a markup module.

This was originally part of
https://github.com/go-gitea/gitea/pull/22177.

Signed-off-by: Nick Guenther <nick.guenther@polymtl.ca>

2 files changed, 120 insertions, 0 deletions

diff --git a/modules/util/path.go b/modules/util/path.go
index e060b527f3..74acb7a85f 100644
--- a/modules/util/path.go
+++ b/modules/util/path.go
@@ -11,6 +11,7 @@ import (
 	"path/filepath"
 	"regexp"
 	"runtime"
+	"strings"
 )
 
 // EnsureAbsolutePath ensure that a path is absolute, making it
@@ -201,3 +202,41 @@ func CommonSkip(name string) bool {
 
 	return false
 }
+
+// IsReadmeFileName reports whether name looks like a README file
+// based on its name.
+func IsReadmeFileName(name string) bool {
+	name = strings.ToLower(name)
+	if len(name) < 6 {
+		return false
+	} else if len(name) == 6 {
+		return name == "readme"
+	}
+	return name[:7] == "readme."
+}
+
+// IsReadmeFileExtension reports whether name looks like a README file
+// based on its name. It will look through the provided extensions and check if the file matches
+// one of the extensions and provide the index in the extension list.
+// If the filename is `readme.` with an unmatched extension it will match with the index equaling
+// the length of the provided extension list.
+// Note that the '.' should be provided in ext, e.g ".md"
+func IsReadmeFileExtension(name string, ext ...string) (int, bool) {
+	name = strings.ToLower(name)
+	if len(name) < 6 || name[:6] != "readme" {
+		return 0, false
+	}
+
+	for i, extension := range ext {
+		extension = strings.ToLower(extension)
+		if name[6:] == extension {
+			return i, true
+		}
+	}
+
+	if name[6] == '.' {
+		return len(ext), true
+	}
+
+	return 0, false
+}
diff --git a/modules/util/path_test.go b/modules/util/path_test.go
index 5794df1ebf..93f4f67cf6 100644
--- a/modules/util/path_test.go
+++ b/modules/util/path_test.go
@@ -55,3 +55,84 @@ func TestFileURLToPath(t *testing.T) {
 		}
 	}
 }
+
+func TestMisc_IsReadmeFileName(t *testing.T) {
+	trueTestCases := []string{
+		"readme",
+		"README",
+		"readME.mdown",
+		"README.md",
+		"readme.i18n.md",
+	}
+	falseTestCases := []string{
+		"test.md",
+		"wow.MARKDOWN",
+		"LOL.mDoWn",
+		"test",
+		"abcdefg",
+		"abcdefghijklmnopqrstuvwxyz",
+		"test.md.test",
+		"readmf",
+	}
+
+	for _, testCase := range trueTestCases {
+		assert.True(t, IsReadmeFileName(testCase))
+	}
+	for _, testCase := range falseTestCases {
+		assert.False(t, IsReadmeFileName(testCase))
+	}
+
+	type extensionTestcase struct {
+		name     string
+		expected bool
+		idx      int
+	}
+
+	exts := []string{".md", ".txt", ""}
+	testCasesExtensions := []extensionTestcase{
+		{
+			name:     "readme",
+			expected: true,
+			idx:      2,
+		},
+		{
+			name:     "readme.md",
+			expected: true,
+			idx:      0,
+		},
+		{
+			name:     "README.md",
+			expected: true,
+			idx:      0,
+		},
+		{
+			name:     "ReAdMe.Md",
+			expected: true,
+			idx:      0,
+		},
+		{
+			name:     "readme.txt",
+			expected: true,
+			idx:      1,
+		},
+		{
+			name:     "readme.doc",
+			expected: true,
+			idx:      3,
+		},
+		{
+			name: "readmee.md",
+		},
+		{
+			name:     "readme..",
+			expected: true,
+			idx:      3,
+		},
+	}
+
+	for _, testCase := range testCasesExtensions {
+		idx, ok := IsReadmeFileExtension(testCase.name, exts...)
+		assert.Equal(t, testCase.expected, ok)
+		assert.Equal(t, testCase.idx, idx)
+	}
+}