zaphyra's git: haumea

transformers.prependUnderscore: init

diff --git a/docs/src/api/transformers.md b/docs/src/api/transformers.md
@@ -46,3 +46,12 @@ Type: `[ String ] -> { ... } -> { ... }`
 This transformer will lift the contents of `default` into the module.
 It will fail if `default` is not an attribute set,
 or has any overlapping attributes with the module.
+
+## `transformers.prependUnderscore`
+
+Source: [`src/transformers/prependUnderscore.nix`](https://github.com/nix-community/haumea/blob/main/src/transformers/prependUnderscore.nix)
+
+Type: `[ String ] -> { ... } -> { ... }`
+
+This transformer prepnds `_` to attributes that are not valid identifiers, e.g. `42` -> `_42`.
+Attributes that are already valid identifiers (e.g. `foo`) are left unchanged.

diff --git a/src/transformers/prependUnderscore.nix b/src/transformers/prependUnderscore.nix
@@ -0,0 +1,18 @@
+{ lib }:
+
+let
+  inherit (builtins)
+    substring
+    elem
+    ;
+  inherit (lib)
+    mapAttrs'
+    stringToCharacters
+    nameValuePair
+    ;
+
+  start = stringToCharacters "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz_";
+in
+
+_: mapAttrs' (name: nameValuePair
+  (if elem (substring 0 1 name) start then name else "_${name}"))

diff --git a/tests/prependUnderscore/__fixture/'bar.nix b/tests/prependUnderscore/__fixture/'bar.nix
@@ -0,0 +1 @@
+"'bar"

diff --git a/tests/prependUnderscore/__fixture/0foo/bar.nix b/tests/prependUnderscore/__fixture/0foo/bar.nix
@@ -0,0 +1 @@
+"0foo.bar"

diff --git a/tests/prependUnderscore/__fixture/baz.nix b/tests/prependUnderscore/__fixture/baz.nix
@@ -0,0 +1 @@
+"baz"

diff --git a/tests/prependUnderscore/expected.nix b/tests/prependUnderscore/expected.nix
@@ -0,0 +1,5 @@
+{
+  _0foo.bar = "0foo.bar";
+  _'bar = "'bar";
+  baz = "baz";
+}

diff --git a/tests/prependUnderscore/expr.nix b/tests/prependUnderscore/expr.nix
@@ -0,0 +1,6 @@
+{ haumea }:
+
+haumea.load {
+  src = ./__fixture;
+  transformer = haumea.transformers.prependUnderscore;
+}