Support Num.toStr for dec

crates/compiler/builtins/bitcode/src/dec.zig

@@ -131,7 +131,7 @@ pub const RocDec = extern struct {
         return (c -% 48) <= 9;
     }
 
-    pub fn toStr(self: RocDec) ?RocStr {
+    pub fn toStr(self: RocDec) RocStr {
         // Special case
         if (self.num == 0) {
             return RocStr.init("0.0", 3);
@@ -1065,6 +1065,10 @@ pub fn fromStr(arg: RocStr) callconv(.C) num_.NumParseResult(i128) {
     }
 }
 
+pub fn toStr(arg: RocDec) callconv(.C) RocStr {
+    return @call(.{ .modifier = always_inline }, RocDec.toStr, .{arg});
+}
+
 pub fn fromF64C(arg: f64) callconv(.C) i128 {
     return if (@call(.{ .modifier = always_inline }, RocDec.fromF64, .{arg})) |dec| dec.num else @panic("TODO runtime exception failing convert f64 to RocDec");
 }

crates/compiler/builtins/bitcode/src/main.zig

@@ -12,6 +12,7 @@ const dec = @import("dec.zig");
 
 comptime {
     exportDecFn(dec.fromStr, "from_str");
+    exportDecFn(dec.toStr, "to_str");
     exportDecFn(dec.fromF64C, "from_f64");
     exportDecFn(dec.eqC, "eq");
     exportDecFn(dec.neqC, "neq");

crates/compiler/builtins/src/bitcode.rs

@@ -372,6 +372,7 @@ pub const LIST_APPEND_UNSAFE: &str = "roc_builtins.list.append_unsafe";
 pub const LIST_RESERVE: &str = "roc_builtins.list.reserve";
 
 pub const DEC_FROM_STR: &str = "roc_builtins.dec.from_str";
+pub const DEC_TO_STR: &str = "roc_builtins.dec.to_str";
 pub const DEC_FROM_F64: &str = "roc_builtins.dec.from_f64";
 pub const DEC_EQ: &str = "roc_builtins.dec.eq";
 pub const DEC_NEQ: &str = "roc_builtins.dec.neq";

crates/compiler/gen_llvm/src/llvm/build.rs

@@ -13,7 +13,7 @@ use crate::llvm::build_list::{
     list_replace_unsafe, list_reserve, list_sort_with, list_sublist, list_swap,
     list_symbol_to_c_abi, list_to_c_abi, list_with_capacity, pass_update_mode,
 };
-use crate::llvm::build_str::{str_from_float, str_from_int};
+use crate::llvm::build_str::{dec_to_str, str_from_float, str_from_int};
 use crate::llvm::compare::{generic_eq, generic_neq};
 use crate::llvm::convert::{
     self, argument_type_from_layout, basic_type_from_builtin, basic_type_from_layout,
@@ -5825,6 +5825,7 @@ fn run_low_level<'a, 'ctx, 'env>(
                 Layout::Builtin(Builtin::Float(float_width)) => {
                     str_from_float(env, num, *float_width)
                 }
+                Layout::Builtin(Builtin::Decimal) => dec_to_str(env, num),
                 _ => unreachable!(),
             }
         }

crates/compiler/gen_llvm/src/llvm/build_str.rs

@@ -112,10 +112,28 @@ pub fn str_from_float<'a, 'ctx, 'env>(
     call_str_bitcode_fn(env, &[float], &bitcode::STR_FROM_FLOAT[float_width])
 }
 
+/// Dec.toStr : Dec -> Str
+pub fn dec_to_str<'a, 'ctx, 'env>(
+    env: &Env<'a, 'ctx, 'env>,
+    dec: BasicValueEnum<'ctx>,
 ) -> BasicValueEnum<'ctx> {
-    let float = load_symbol(scope, &int_symbol);
+    let dec = dec.into_int_value();
 
-    call_str_bitcode_fn(env, &[float], bitcode::STR_FROM_FLOAT)
+    let int_64 = env.context.i128_type().const_int(64, false);
+    let int_64_type = env.context.i64_type();
+
+    let dec_right_shift = env
+        .builder
+        .build_right_shift(dec, int_64, false, "dec_left_bits");
+
+    let right_bits = env.builder.build_int_cast(dec, int_64_type, "");
+    let left_bits = env.builder.build_int_cast(dec_right_shift, int_64_type, "");
+
+    call_str_bitcode_fn(
+        env,
+        &[right_bits.into(), left_bits.into()],
+        bitcode::DEC_TO_STR,
+    )
 }
 
 /// Str.equal : Str, Str -> Bool

crates/compiler/test_gen/src/gen_num.rs

@@ -3102,6 +3102,30 @@ fn num_to_str_f64() {
     );
 }
 
+#[test]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
+fn num_to_str_dec() {
+    use roc_std::RocStr;
+
+    assert_evals_to!(r#"Num.toStr -10.75dec"#, RocStr::from("-10.75"), RocStr);
+    assert_evals_to!(r#"Num.toStr -1.75dec"#, RocStr::from("-1.75"), RocStr);
+    assert_evals_to!(r#"Num.toStr 0dec"#, RocStr::from("0.0"), RocStr);
+    assert_evals_to!(r#"Num.toStr 1.75dec"#, RocStr::from("1.75"), RocStr);
+    assert_evals_to!(r#"Num.toStr 10.75dec"#, RocStr::from("10.75"), RocStr);
+
+    assert_evals_to!(
+        r#"Num.toStr 170141183460469.105727dec"#,
+        RocStr::from("170141183460469.105727"),
+        RocStr
+    );
+
+    assert_evals_to!(
+        r#"Num.toStr -170141183460469.105727dec"#,
+        RocStr::from("-170141183460469.105727"),
+        RocStr
+    );
+}
+
 #[test]
 #[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn u8_addition_greater_than_i8() {