resolve: Normalize

This means "../" components are cancelled out even after non-existent
paths or files.

(the alternative is to error out, but being able to say `path resolve
/path/to/file/../../` over `path resolve (path dirname
/path/to/file)/../../` seems worth it?)

src/builtins/path.cpp

@@ -675,6 +675,11 @@ static int path_resolve(parser_t &parser, io_streams_t &streams, int argc, const
             }
         }
 
+        // Normalize the path so "../" components are eliminated even after
+        // nonexistent or non-directory components.
+        // Otherwise `path resolve foo/../` will be `$PWD/foo/../` if foo is a file.
+        real = normalize_path(*real, false);
+
         // Return 0 if we found a realpath.
         if (opts.quiet) {
             return STATUS_CMD_OK;

tests/checks/path.fish

@@ -118,6 +118,10 @@ path resolve bin//sh | string match -r -- 'bin/bash$'
 # sh here is bash
 # CHECK: bin/bash
 
+# "../" cancels out even files.
+path resolve bin//sh/../ | string match -r -- 'bin$'
+# CHECK: bin
+
 # `path resolve` with nonexistent paths
 set -l path (path resolve foo/bar)
 string match -rq "^"(pwd -P | string escape --style=regex)'/' -- $path