Str.reserve

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

@@ -157,6 +157,7 @@ comptime {
     exportStrFn(str.strEqual, "equal");
     exportStrFn(str.substringUnsafe, "substring_unsafe");
     exportStrFn(str.getUnsafe, "get_unsafe");
+    exportStrFn(str.reserve, "reserve");
     exportStrFn(str.strToUtf8C, "to_utf8");
     exportStrFn(str.fromUtf8C, "from_utf8");
     exportStrFn(str.fromUtf8RangeC, "from_utf8_range");

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

@@ -2446,3 +2446,11 @@ test "appendScalar: big 😀" {
 
     try expect(actual.eq(expected));
 }
+
+pub fn reserve(string: RocStr, capacity: usize) callconv(.C) RocStr {
+    if (capacity > string.capacity()) {
+        return string.reallocate(capacity);
+    } else {
+        return string;
+    }
+}

crates/compiler/builtins/roc/Str.roc

@@ -37,6 +37,7 @@ interface Str
             splitFirst,
             splitLast,
             walkUtf8WithIndex,
+            reserve
         ]
     imports [Bool.{ Bool }, Result.{ Result }]
 
@@ -341,3 +342,6 @@ walkUtf8WithIndexHelp = \string, state, step, index, length ->
         walkUtf8WithIndexHelp string newState step (index + 1) length
     else
         state
+
+## Make sure at least some number of bytes fit in this string without reallocating
+reserve : Str, Nat -> Str

crates/compiler/builtins/src/bitcode.rs

@@ -333,6 +333,7 @@ pub const STR_TRIM: &str = "roc_builtins.str.trim";
 pub const STR_TRIM_LEFT: &str = "roc_builtins.str.trim_left";
 pub const STR_TRIM_RIGHT: &str = "roc_builtins.str.trim_right";
 pub const STR_GET_UNSAFE: &str = "roc_builtins.str.get_unsafe";
+pub const STR_RESERVE: &str = "roc_builtins.str.reserve";
 
 pub const DICT_HASH: &str = "roc_builtins.dict.hash";
 pub const DICT_HASH_STR: &str = "roc_builtins.dict.hash_str";