add substringUnsafe roc function

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

@@ -155,6 +155,7 @@ comptime {
     exportStrFn(str.strNumberOfBytes, "number_of_bytes");
     exportStrFn(str.strFromFloatC, "from_float");
     exportStrFn(str.strEqual, "equal");
+    exportStrFn(str.substringUnsafe, "substring_unsafe");
     exportStrFn(str.strToUtf8C, "to_utf8");
     exportStrFn(str.fromUtf8C, "from_utf8");
     exportStrFn(str.fromUtf8RangeC, "from_utf8_range");

crates/compiler/builtins/roc/Str.roc

@@ -224,3 +224,9 @@ toI8 : Str -> Result I8 [InvalidNumStr]*
 
 ## Gets the byte at the given index, without performing a bounds check
 getUnsafe : Str, Nat -> U8
+
+## gives the number of string bytes
+countBytes : Str -> Nat
+
+## string slice that does not do bounds checking or utf-8 verification
+substringUnsafe : Str, Nat, Nat -> Str

crates/compiler/builtins/src/bitcode.rs

@@ -324,6 +324,7 @@ pub const STR_TO_INT: IntrinsicName = int_intrinsic!("roc_builtins.str.to_int");
 pub const STR_TO_FLOAT: IntrinsicName = float_intrinsic!("roc_builtins.str.to_float");
 pub const STR_TO_DECIMAL: &str = "roc_builtins.str.to_decimal";
 pub const STR_EQUAL: &str = "roc_builtins.str.equal";
+pub const STR_SUBSTRING_UNSAFE: &str = "roc_builtins.str.substring_unsafe";
 pub const STR_TO_UTF8: &str = "roc_builtins.str.to_utf8";
 pub const STR_FROM_UTF8: &str = "roc_builtins.str.from_utf8";
 pub const STR_FROM_UTF8_RANGE: &str = "roc_builtins.str.from_utf8_range";

crates/compiler/can/src/builtins.rs

@@ -82,6 +82,7 @@ pub fn builtin_defs_map(symbol: Symbol, var_store: &mut VarStore) -> Option<Def>
         STR_ENDS_WITH => str_ends_with,
         STR_COUNT_GRAPHEMES => str_count_graphemes,
         STR_COUNT_BYTES=> str_count_bytes,
+        STR_SUBSTRING_UNSAFE => str_substring_unsafe,
         STR_FROM_UTF8 => str_from_utf8,
         STR_FROM_UTF8_RANGE => str_from_utf8_range,
         STR_TO_UTF8 => str_to_utf8,
@@ -1731,6 +1732,11 @@ fn str_count_bytes(symbol: Symbol, var_store: &mut VarStore) -> Def {
     lowlevel_1(symbol, LowLevel::StrCountBytes, var_store)
 }
 
+/// Str.substringUnsafe : Str, Nat, Nat -> Nat
+fn str_substring_unsafe(symbol: Symbol, var_store: &mut VarStore) -> Def {
+    lowlevel_1(symbol, LowLevel::StrSubstringUnsafe, var_store)
+}
+
 /// Str.fromUtf8 : List U8 -> Result Str [BadUtf8 { byteIndex : Nat, problem : Utf8Problem  } }]*
 fn str_from_utf8(symbol: Symbol, var_store: &mut VarStore) -> Def {
     let bytes_var = var_store.fresh();

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

@@ -5347,6 +5347,15 @@ fn run_low_level<'a, 'ctx, 'env>(
             let string = load_symbol(scope, &args[0]);
             call_bitcode_fn(env, &[string], bitcode::STR_COUNT_BYTES)
         }
+        StrSubstringUnsafe => {
+            // Str.substringUnsafe : Str, Nat, Nat -> Str
+            debug_assert_eq!(args.len(), 3);
+
+            let string = load_symbol(scope, &args[0]);
+            let start = load_symbol(scope, &args[1]);
+            let length = load_symbol(scope, &args[2]);
+            call_str_bitcode_fn(env, &[string, start, length], bitcode::STR_SUBSTRING_UNSAFE)
+        }
         StrTrim => {
             // Str.trim : Str -> Str
             debug_assert_eq!(args.len(), 1);

crates/compiler/gen_wasm/src/low_level.rs

@@ -277,6 +277,9 @@ impl<'a> LowLevelCall<'a> {
             StrToUtf8 => self.load_args_and_call_zig(backend, bitcode::STR_TO_UTF8),
             StrRepeat => self.load_args_and_call_zig(backend, bitcode::STR_REPEAT),
             StrTrim => self.load_args_and_call_zig(backend, bitcode::STR_TRIM),
+            StrSubstringUnsafe => {
+                self.load_args_and_call_zig(backend, bitcode::STR_SUBSTRING_UNSAFE)
+            }
 
             // List
             ListLen => match backend.storage.get(&self.arguments[0]) {

crates/compiler/module/src/low_level.rs

@@ -26,6 +26,7 @@ pub enum LowLevel {
     StrToNum,
     StrToScalars,
     StrGetUnsafe,
+    StrSubstringUnsafe,
     ListLen,
     ListWithCapacity,
     ListGetUnsafe,

crates/compiler/module/src/symbol.rs

@@ -1192,6 +1192,7 @@ define_builtins! {
         34 STR_TO_SCALARS: "toScalars"
         35 STR_GET_UNSAFE: "getUnsafe"
         36 STR_COUNT_BYTES: "countBytes"
+        37 STR_SUBSTRING_UNSAFE: "substringUnsafe"
     }
     5 LIST: "List" => {
         0 LIST_LIST: "List" imported // the List.List type alias

crates/compiler/mono/src/borrow.rs

@@ -895,6 +895,7 @@ pub fn lowlevel_borrow_signature(arena: &Bump, op: LowLevel) -> &[bool] {
         StrGetUnsafe | ListGetUnsafe => arena.alloc_slice_copy(&[borrowed, irrelevant]),
         ListConcat => arena.alloc_slice_copy(&[owned, owned]),
         StrConcat => arena.alloc_slice_copy(&[owned, borrowed]),
+        StrSubstringUnsafe => arena.alloc_slice_copy(&[owned]),
         StrTrim => arena.alloc_slice_copy(&[owned]),
         StrTrimLeft => arena.alloc_slice_copy(&[owned]),
         StrTrimRight => arena.alloc_slice_copy(&[owned]),