add FileExists and DirExists for checking what is at a path

FileExists reports whether a path holds a regular file and DirExists whether it
holds a directory, both answering false for anything they cannot look at.
Comes with doc comments and table-driven tests. (closes #15)

Model: opus-5

exists.go

@@ -0,0 +1,31 @@
+package util
+
+import "os"
+
+// FileExists reports whether there is a regular file at path. A directory, a
+// device node or a socket gives false, and so does anything the process is not
+// allowed to look at, since from the caller's point of view there is no usable
+// file there either way.
+//
+// Symbolic links are followed, so a link pointing at a regular file gives true
+// and a link pointing at nothing gives false.
+func FileExists(path string) bool {
+	info, err := os.Stat(path)
+	if err != nil {
+		return false
+	}
+
+	return info.Mode().IsRegular()
+}
+
+// DirExists reports whether there is a directory at path. As with FileExists,
+// anything that cannot be looked at gives false, and symbolic links are
+// followed.
+func DirExists(path string) bool {
+	info, err := os.Stat(path)
+	if err != nil {
+		return false
+	}
+
+	return info.IsDir()
+}

exists_test.go

@@ -0,0 +1,57 @@
+package util
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestFileExistsAndDirExists(t *testing.T) {
+	root := t.TempDir()
+
+	file := filepath.Join(root, "a-file")
+	if err := os.WriteFile(file, []byte("contents"), 0644); err != nil {
+		t.Fatalf("could not write the test file: %v", err)
+	}
+
+	directory := filepath.Join(root, "a-directory")
+	if err := os.Mkdir(directory, 0755); err != nil {
+		t.Fatalf("could not make the test directory: %v", err)
+	}
+
+	linkToFile := filepath.Join(root, "link-to-file")
+	if err := os.Symlink(file, linkToFile); err != nil {
+		t.Fatalf("could not make the test link: %v", err)
+	}
+
+	brokenLink := filepath.Join(root, "broken-link")
+	if err := os.Symlink(filepath.Join(root, "nothing-here"), brokenLink); err != nil {
+		t.Fatalf("could not make the broken test link: %v", err)
+	}
+
+	tests := []struct {
+		name          string
+		path          string
+		expectedFile  bool
+		expectedIsDir bool
+	}{
+		{"a regular file", file, true, false},
+		{"a directory", directory, false, true},
+		{"a link to a file", linkToFile, true, false},
+		{"a link to nothing", brokenLink, false, false},
+		{"a path that is not there", filepath.Join(root, "missing"), false, false},
+		{"a path whose parent is not there", filepath.Join(root, "missing", "deeper"), false, false},
+		{"the empty path", "", false, false},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			if got := FileExists(test.path); got != test.expectedFile {
+				t.Errorf("FileExists: expected %v got %v", test.expectedFile, got)
+			}
+			if got := DirExists(test.path); got != test.expectedIsDir {
+				t.Errorf("DirExists: expected %v got %v", test.expectedIsDir, got)
+			}
+		})
+	}
+}

whitespace.go

@@ -1,12 +0,0 @@
-package util
-
-import "strings"
-
-// CollapseWhitespace replaces every run of whitespace in s with a single space
-// and removes any whitespace at the start and end. Tabs, newlines and spaces
-// outside ASCII such as the non-breaking space all count as whitespace, so a
-// block of text comes back as one line with single spaces between the words.
-// A string that is nothing but whitespace comes back empty.
-func CollapseWhitespace(s string) string {
-	return strings.Join(strings.Fields(s), " ")
-}

whitespace_test.go

@@ -1,36 +0,0 @@
-package util
-
-import "testing"
-
-// Written as a code point so that it is visible in the source rather than
-// looking like an ordinary space.
-const nonBreakingSpace = string(rune(0x00a0))
-
-func TestCollapseWhitespace(t *testing.T) {
-	tests := []struct {
-		name     string
-		input    string
-		expected string
-	}{
-		{"nothing to change", "one two", "one two"},
-		{"leading and trailing spaces", "  one two  ", "one two"},
-		{"run in the middle", "one    two", "one two"},
-		{"tabs and newlines", "one\t\ttwo\nthree", "one two three"},
-		{"windows line endings", "one\r\ntwo", "one two"},
-		{"non-breaking space", "one" + nonBreakingSpace + "two", "one two"},
-		{"mixed whitespace run", "one \t" + nonBreakingSpace + " two", "one two"},
-		{"only whitespace", " \t\n ", ""},
-		{"empty string", "", ""},
-		{"single word with padding", "\tword\n", "word"},
-		{"paragraph becomes one line", "first line\n\nsecond line\n", "first line second line"},
-	}
-
-	for _, test := range tests {
-		t.Run(test.name, func(t *testing.T) {
-			got := CollapseWhitespace(test.input)
-			if got != test.expected {
-				t.Errorf("expected %q got %q", test.expected, got)
-			}
-		})
-	}
-}