Change wrealpath to return a maybe_t

Simplify the wrealpath interface and avoid manual invocations of free() by
changing wrealpath to return a maybe_t<wcstring>.

src/builtin_realpath.cpp

@@ -37,10 +37,8 @@ int builtin_realpath(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
         return STATUS_INVALID_ARGS;
     }
 
-    wchar_t *real_path = wrealpath(argv[optind], NULL);
+    if (auto real_path = wrealpath(argv[optind])) {
-    if (real_path) {
+        streams.out.append(*real_path);
-        streams.out.append(real_path);
-        free((void *)real_path);
     } else {
         // We don't actually know why it failed. We should check errno.
         streams.err.append_format(_(L"%ls: Invalid path: %ls\n"), cmd, argv[optind]);

src/expand.cpp

@@ -1182,13 +1182,15 @@ static void expand_home_directory(wcstring &input) {
             }
         }
 
-        const wchar_t *realhome = home ? wrealpath(home->as_string(), NULL) : nullptr;
+        maybe_t<wcstring> realhome;
+        if (home)
+            realhome = wrealpath(home->as_string());
+
         if (realhome) {
-            input.replace(input.begin(), input.begin() + tail_idx, realhome);
+            input.replace(input.begin(), input.begin() + tail_idx, *realhome);
         } else {
             input[0] = L'~';
         }
-        free((void *)realhome);
     }
 }
 

src/wutil.cpp

@@ -338,10 +338,10 @@ void safe_perror(const char *message) {
     errno = err;
 }
 
-wchar_t *wrealpath(const wcstring &pathname, wchar_t *resolved_path) {
+maybe_t<wcstring> wrealpath(const wcstring &pathname) {
-    if (pathname.size() == 0) return NULL;
+    if (pathname.empty()) return none();
 
-    cstring real_path("");
+    cstring real_path;
     cstring narrow_path = wcs2string(pathname);
 
     // Strip trailing slashes. This is needed to be bug-for-bug compatible with GNU realpath which
@@ -370,7 +370,7 @@ wchar_t *wrealpath(const wcstring &pathname, wchar_t *resolved_path) {
             } else {
                 // Only call realpath() on the portion up to the last component.
                 narrow_res = realpath(narrow_path.substr(0, pathsep_idx).c_str(), tmpbuff);
-                if (!narrow_res) return NULL;
+                if (!narrow_res) return none();
                 pathsep_idx++;
             }
             real_path.append(narrow_res);
@@ -379,12 +379,7 @@ wchar_t *wrealpath(const wcstring &pathname, wchar_t *resolved_path) {
             real_path.append(narrow_path.substr(pathsep_idx, cstring::npos));
         }
     }
-    wcstring wreal_path = str2wcstring(real_path);
+    return str2wcstring(real_path);
-    if (resolved_path) {
-        wcslcpy(resolved_path, wreal_path.c_str(), PATH_MAX);
-        return resolved_path;
-    }
-    return wcsdup(wreal_path.c_str());
 }
 
 wcstring wdirname(const wcstring &path) {

src/wutil.h

@@ -10,6 +10,7 @@
 #include <string>
 
 #include "common.h"
+#include "maybe.h"
 
 /// Wide character version of fopen(). This sets CLO_EXEC.
 FILE *wfopen(const wcstring &path, const char *mode);
@@ -58,10 +59,9 @@ const wcstring wgetcwd();
 /// Wide character version of chdir().
 int wchdir(const wcstring &dir);
 
-/// Wide character version of realpath function. Just like the GNU version of realpath, wrealpath
+/// Wide character version of realpath function.
-/// will accept 0 as the value for the second argument, in which case the result will be allocated
+/// \returns the canonicalized path, or none if the path is invalid.
-/// using malloc, and must be free'd by the user.
+maybe_t<wcstring> wrealpath(const wcstring &pathname);
-wchar_t *wrealpath(const wcstring &pathname, wchar_t *resolved_path);
 
 /// Wide character version of readdir().
 bool wreaddir(DIR *dir, wcstring &out_name);