Dicts passed to set_cfg_constructor stage0 callback should not be sorted

The commands below show that the dict passed to the `package_modifiers` argument of the set_cfg_constructor stage0 was sorted. This reordering is a problem because it causes `cfg.conditional` modifiers to resolve in an unexpected manner.

For example: I would expect the below modifier to leave the configuration unchanged if "cfg//c:y" and "cfg//a:y" were both set, but the sorting behaviour breaks this.

```bzl
set_cfg_modifers(modifiers = [
modifiers.conditional({
"cfg//c:y": None,
"cfg//b:y": None,
"cfg//a:y": "cfg//ftr_foo:y",
})
])
```

## Minimal example

```
timorland-local@DUS-MXL3312NDR:/tmp/modifiers-problem$ git format-patch -1 --stdout
.buckconfig | 2 ++
.buckroot | 0
.gitignore | 1 +
BUCK | 3 +++
PACKAGE | 18 ++++++++++++++++++
defs.bzl | 28 ++++++++++++++++++++++++++++
6 files changed, 52 insertions(+)
create mode 100644 .buckconfig
create mode 100644 .buckroot
create mode 100644 .gitignore
create mode 100644 BUCK
create mode 100644 PACKAGE
create mode 100644 defs.bzl

diff --git a/.buckconfig b/.buckconfig
new file mode 100644
index 0000000..82ff4e5
--- /dev/null
+++ b/.buckconfig
@@ -0,0 +1,2 @@
+[cells]
+ root = .
diff --git a/.buckroot b/.buckroot
new file mode 100644
index 0000000..e69de29
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..d60c5d2
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+buck-out
diff --git a/BUCK b/BUCK
new file mode 100644
index 0000000..3cf47b4
--- /dev/null
+++ b/BUCK
@@ -0,0 +1,3 @@
+load(":defs.bzl", "nothing")
+
+nothing(name = "top")
diff --git a/PACKAGE b/PACKAGE
new file mode 100644
index 0000000..975e8d0
--- /dev/null
+++ b/PACKAGE
@@ -0,0 +1,18 @@
+load(":defs.bzl", "stage0", "stage1")
+
+set_cfg_constructor(
+ stage0 = stage0,
+ stage1 = stage1,
+ key = "buck.modifiers",
+ aliases = struct(),
+)
+
+write_package_value(
+ "buck.modifiers",
+ [
+ {
+ "b": "This should be first",
+ "a": "This should be second",
+ },
+ ],
+)
diff --git a/defs.bzl b/defs.bzl
new file mode 100644
index 0000000..b1bf623
--- /dev/null
+++ b/defs.bzl
@@ -0,0 +1,28 @@
+nothing = rule(
+ impl = lambda ctx: [DefaultInfo()],
+ attrs = {},
+)
+
+def stage0(*, legacy_platform, package_modifiers, target_modifiers, cli_modifiers, rule_name, aliases, **_kwargs):
+ print(
+ "stage0_args =",
+ pstr({
+ "legacy_platform": legacy_platform,
+ "package_modifiers": package_modifiers,
+ "target_modifiers": target_modifiers,
+ "cli_modifiers": cli_modifiers,
+ "rule_name": rule_name,
+ "aliases": aliases,
+ }),
+ )
+
+ return ([], None)
+
+def stage1(*, refs, params) -> PlatformInfo:
+ return PlatformInfo(
+ label = "",
+ configuration = ConfigurationInfo(
+ constraints = {},
+ values = {},
+ ),
+ )
--
2.45.GIT

timorland-local@DUS-MXL3312NDR:/tmp/modifiers-problem$ buck2 build :
Could not connect to buck2 daemon (buck2 daemon is not running), starting a new one...
Connected to new buck2 daemon.
stage0_args = {
"legacy_platform": None,
"package_modifiers": [ {
"a": "This should be second",
"b": "This should be first"
} ],
"target_modifiers": None,
"cli_modifiers": [],
"rule_name": "nothing",
"aliases": struct()
}
Build ID: 1db24b5a-121c-4d48-ac22-bfb6d3783b2d
Jobs completed: 5. Time elapsed: 0.0s.
BUILD SUCCEEDED
```