Merge pull request #75584 from Infinisil/settings-formats

Configuration file formats for JSON, INI, YAML and TOML

lib/generators.nix

@@ -48,8 +48,10 @@ rec {
     else if isAttrs    v then err "attrsets" v
     # functions can’t be printed of course
     else if isFunction v then err "functions" v
-    # let’s not talk about floats. There is no sensible `toString` for them.
-    else if isFloat    v then err "floats" v
+    # Floats currently can't be converted to precise strings,
+    # condition warning on nix version once this isn't a problem anymore
+    # See https://github.com/NixOS/nix/pull/3480
+    else if isFloat    v then libStr.floatToString v
     else err "this value is" (toString v);
 
 

lib/strings.nix

@@ -612,6 +612,22 @@ rec {
   */
   fixedWidthNumber = width: n: fixedWidthString width "0" (toString n);
 
+  /* Convert a float to a string, but emit a warning when precision is lost
+     during the conversion
+
+     Example:
+       floatToString 0.000001
+       => "0.000001"
+       floatToString 0.0000001
+       => trace: warning: Imprecise conversion from float to string 0.000000
+          "0.000000"
+  */
+  floatToString = float: let
+    result = toString float;
+    precise = float == builtins.fromJSON result;
+  in if precise then result
+    else lib.warn "Imprecise conversion from float to string ${result}" result;
+
   /* Check whether a value can be coerced to a string */
   isCoercibleToString = x:
     builtins.elem (builtins.typeOf x) [ "path" "string" "null" "int" "float" "bool" ] ||