cmd-diff: support cd strategy for diff_cmd_outputs

This strategy simply changes directory into the given path before
running the provided command rather than replacing a templated `{}`
with the path.

Useful for commands that operate more cleanly when operated on in
the directory where you want the operation to occur.

Author: dustymabe

src/cmd-diff

@@ -401,16 +401,21 @@ def diff_metal(diff_from, diff_to):
         shutdown_process(p_to)
 
 
-def diff_cmd_outputs(cmd, path_from, path_to):
+def diff_cmd_outputs(cmd, path_from, path_to, strategy='template'):
+    workingdir = os.getcwd()
     with tempfile.NamedTemporaryFile(prefix=cmd[0] + '-') as from_output, \
          tempfile.NamedTemporaryFile(prefix=cmd[0] + '-') as to_output:
         for path, output in (path_from, from_output), (path_to, to_output):
             c = list(cmd)
-            if '{}' not in c:
-                c += ['{}']
-            idx = c.index('{}')
-            c[idx] = path
-            subprocess.run(c, check=True, stdout=output).stdout
+            if strategy == 'template':
+                if '{}' not in c:
+                    c += ['{}']
+                idx = c.index('{}')
+                c[idx] = path
+            else:
+                assert strategy == 'cd'
+                workingdir = path
+            subprocess.run(c, cwd=workingdir, check=True, stdout=output).stdout
         git_diff(from_output.name, to_output.name)