Make 'eden config' print valid TOML

Summary:
The 'eden config' command prints output naively. This leads to confusing output when using the hg.extra_hgrc option. For example, in the following output, `mode = off` is part of hg.extra_hgrc's value, but it looks like it's a separate option in Eden's config:

```
$ eden config
[clone]
default-revision=master
[rage]
reporter=pastry --title "eden rage from $(hostname)"
[hg]
extra_hgrc=[fsmonitor]
mode = off

%include /etc/mercurial/repo-specific/eden.rc
[service]
experimental_systemd=True
```

Fix this issue by making 'eden config' output valid TOML:

```
[clone]
default-revision = "master"

[rage]
reporter = "pastry --title \"eden rage from $(hostname)\""

[hg]
extra_hgrc = "[fsmonitor]\nmode = off\n\n%include /etc/mercurial/repo-specific/eden.rc\n"

[service]
experimental_systemd = "True"
```

Reviewed By: simpkins

Differential Revision: D13661229

fbshipit-source-id: 76e4fa83ad186d04451623e3d8d87a78e4b821d8

eden/cli/config.py

@@ -246,12 +246,12 @@ class EdenInstance:
             pass
         return False
 
-    def print_full_config(self) -> None:
+    def print_full_config(self, file: typing.TextIO) -> None:
         parser = self._loadConfig()
+        data: Dict[str, Dict[str, str]] = {}
         for section in parser.sections():
-            print("[%s]" % section)
-            for k, v in parser.items(section):
-                print("%s=%s" % (k, v))
+            data[section] = {k: v for k, v in parser.items(section)}
+        toml.dump(data, file)  # pyre-ignore[T39129461]
 
     def find_config_for_alias(self, alias: str) -> Optional[CheckoutConfig]:
         """Looks through the existing config files and searches for a

eden/cli/main.py

@@ -418,7 +418,7 @@ class ConfigCmd(Subcmd):
                 # mirrors `git config --get invalid`; just exit with code 1
                 return 1
         else:
-            instance.print_full_config()
+            instance.print_full_config(file=sys.stdout)
         return 0
 
 

eden/cli/test/config_test.py

@@ -9,6 +9,7 @@
 
 import abc
 import configparser
+import io
 import os
 import unittest
 from typing import Dict, List, Optional
@@ -304,6 +305,36 @@ experimental_systemd = false
         )
         self.assertFalse(self.get_config().should_use_experimental_systemd_mode())
 
+    def test_printed_config_is_valid_toml(self) -> None:
+        self.write_user_config(
+            """
+[clone]
+default-revision = "master"
+"""
+        )
+
+        printed_config = io.StringIO()
+        self.get_config().print_full_config(file=printed_config)
+        printed_config.seek(0)
+        parsed_config = toml.load(printed_config)
+
+        self.assertIn("clone", parsed_config)
+        self.assertEqual(parsed_config["clone"].get("default-revision"), "master")
+
+    def test_printed_config_expands_variables(self) -> None:
+        self.write_user_config(
+            """
+["repository fbsource"]
+type = "hg"
+path = "/data/users/${USER}/fbsource"
+"""
+        )
+
+        printed_config = io.StringIO()
+        self.get_config().print_full_config(file=printed_config)
+
+        self.assertIn("/data/users/bob/fbsource", printed_config.getvalue())
+
     def get_config(self) -> EdenInstance:
         return EdenInstance(
             self._state_dir, self._etc_eden_dir, self._home_dir, self._interpolate_dict