Expand relative paths in shell.MakeDirectories

This function needed defined behavior for relative paths. For example,
the default log directory for Postgres is just "log" which it interprets
relative to the data directory.

Issue: PGO-2558

Author: cbandy

internal/shell/paths.go

@@ -36,6 +36,8 @@ func CleanFileName(path string) string {
 // exists. It creates every directory leading to path from (but not including)
 // base and sets their permissions for Kubernetes, regardless of umask.
 //
+// Relative paths are expanded relative to base.
+//
 // See:
 //   - https://pubs.opengroup.org/onlinepubs/9799919799/utilities/chmod.html
 //   - https://pubs.opengroup.org/onlinepubs/9799919799/utilities/mkdir.html
@@ -47,8 +49,17 @@ func MakeDirectories(base string, paths ...string) string {
 		return `test -d ` + QuoteWord(base)
 	}
 
-	allPaths := slices.Clone(paths)
-	for _, p := range paths {
+	// Expand each path relative to the base path.
+	expandedPaths := slices.Clone(paths)
+	for i, p := range expandedPaths {
+		if !filepath.IsAbs(p) {
+			expandedPaths[i] = filepath.Join(base, p)
+		}
+	}
+
+	// Gather parent directories of each path.
+	allPaths := slices.Clone(expandedPaths)
+	for _, p := range expandedPaths {
 		if r, err := filepath.Rel(base, p); err == nil && filepath.IsLocal(r) {
 			// The result of [filepath.Rel] is a shorter representation of the full path; skip it.
 			r = filepath.Dir(r)
@@ -72,7 +83,7 @@ func MakeDirectories(base string, paths ...string) string {
 
 	return `` +
 		// Create all the paths and any missing parents.
-		`mkdir -p ` + strings.Join(QuoteWords(paths...), " ") +
+		`mkdir -p ` + strings.Join(QuoteWords(expandedPaths...), " ") +
 
 		// Try to set the permissions of every path and each parent.
 		// This swallows the exit status of `chmod` because not all filesystems

internal/shell/paths_test.go

@@ -94,6 +94,38 @@ func TestMakeDirectories(t *testing.T) {
 		})
 	})
 
+	t.Run("Relative", func(t *testing.T) {
+		assert.Equal(t,
+			MakeDirectories("/x", "one", "two/three"),
+			`mkdir -p '/x/one' '/x/two/three' && { chmod 0775 '/x/one' '/x/two/three' '/x/two' || :; }`,
+			"expected paths relative to base")
+
+		assert.Equal(t,
+			MakeDirectories("/x/y/z", "../one", "./two", "../../../../three"),
+			`mkdir -p '/x/y/one' '/x/y/z/two' '/three' && { chmod 0775 '/x/y/one' '/x/y/z/two' '/three' || :; }`,
+			"expected paths relative to base")
+
+		script := MakeDirectories("x/y", "../one", "./two", "../../../../three")
+		assert.Equal(t, script,
+			`mkdir -p 'x/one' 'x/y/two' '../../three' && { chmod 0775 'x/one' 'x/y/two' '../../three' || :; }`,
+			"expected paths relative to base")
+
+		// Calling `mkdir -p '../..'` works, but run it by ShellCheck as a precaution.
+		t.Run("ShellCheckPOSIX", func(t *testing.T) {
+			shellcheck := require.ShellCheck(t)
+
+			dir := t.TempDir()
+			file := filepath.Join(dir, "script.sh")
+			assert.NilError(t, os.WriteFile(file, []byte(script), 0o600))
+
+			// Expect ShellCheck for "sh" to be happy.
+			// - https://www.shellcheck.net/wiki/SC2148
+			cmd := exec.CommandContext(t.Context(), shellcheck, "--enable=all", "--shell=sh", file)
+			output, err := cmd.CombinedOutput()
+			assert.NilError(t, err, "%q\n%s", cmd.Args, output)
+		})
+	})
+
 	t.Run("Unrelated", func(t *testing.T) {
 		assert.Equal(t,
 			MakeDirectories("/one", "/two/three/four"),