Added String.fromByte with docs and unit test

doc/site/modules/core/string.markdown

@@ -57,6 +57,15 @@ Creates a new string containing the UTF-8 encoding of `codePoint`.
 It is a runtime error if `codePoint` is not an integer between `0` and
 `0x10ffff`, inclusive.
 
+### String.**fromByte**(byte)
+
+Creates a new string containing the single byte `byte`.
+
+    :::wren
+    String.fromByte(255) //> <20>
+
+It is a runtime error if `byte` is not an integer between `0` and `0xff`, inclusive.
+
 ## Methods
 
 ### **bytes**

src/vm/wren_core.c

@@ -920,6 +920,21 @@ DEF_PRIMITIVE(string_fromCodePoint)
   RETURN_VAL(wrenStringFromCodePoint(vm, codePoint));
 }
 
+DEF_PRIMITIVE(string_fromByte)
+{
+  if (!validateInt(vm, args[1], "Byte")) return false;
+  int byte = (int) AS_NUM(args[1]);
+  if (byte < 0)
+  {
+    RETURN_ERROR("Byte cannot be negative.");
+  }
+  else if (byte > 0xff)
+  {
+    RETURN_ERROR("Byte cannot be greater than 0xff.");
+  }
+  RETURN_VAL(wrenStringFromByte(vm, (uint8_t) byte));
+}
+
 DEF_PRIMITIVE(string_byteAt)
 {
   ObjString* string = AS_STRING(args[0]);
@@ -1305,6 +1320,7 @@ void wrenInitializeCore(WrenVM* vm)
 
   vm->stringClass = AS_CLASS(wrenFindVariable(vm, coreModule, "String"));
   PRIMITIVE(vm->stringClass->obj.classObj, "fromCodePoint(_)", string_fromCodePoint);
+  PRIMITIVE(vm->stringClass->obj.classObj, "fromByte(_)", string_fromByte);
   PRIMITIVE(vm->stringClass, "+(_)", string_plus);
   PRIMITIVE(vm->stringClass, "[_]", string_subscript);
   PRIMITIVE(vm->stringClass, "byteAt_(_)", string_byteAt);

src/vm/wren_value.c

@@ -802,6 +802,15 @@ Value wrenStringFromCodePoint(WrenVM* vm, int value)
   return OBJ_VAL(string);
 }
 
+Value wrenStringFromByte(WrenVM *vm, uint8_t value)
+{
+  int length = 1;
+  ObjString* string = allocateString(vm, length);
+  string->value[0] = value;
+  hashString(string);
+  return OBJ_VAL(string);
+}
+
 Value wrenStringFormat(WrenVM* vm, const char* format, ...)
 {
   va_list argList;

src/vm/wren_value.h

@@ -738,6 +738,9 @@ Value wrenStringFormat(WrenVM* vm, const char* format, ...);
 // Creates a new string containing the UTF-8 encoding of [value].
 Value wrenStringFromCodePoint(WrenVM* vm, int value);
 
+// Creates a new string from the integer representation of a byte
+Value wrenStringFromByte(WrenVM* vm, uint8_t value);
+
 // Creates a new string containing the code point in [string] starting at byte
 // [index]. If [index] points into the middle of a UTF-8 sequence, returns an
 // empty string.

test/core/string/from_byte.wren

@@ -0,0 +1,3 @@
+System.print(String.fromByte(65))   // expect: A
+System.print(String.fromByte(0).bytes[0])   // expect: 0
+System.print(String.fromByte(255).bytes[0])   // expect: 255

test/core/string/from_byte_not_int.wren

@@ -0,0 +1 @@
+System.print(String.fromByte(12.34))   // expect runtime error: Byte must be an integer.

test/core/string/from_byte_not_num.wren

@@ -0,0 +1 @@
+System.print(String.fromByte("not num"))   // expect runtime error: Byte must be a number.

test/core/string/from_byte_too_large.wren

@@ -0,0 +1 @@
+System.print(String.fromByte(0xff + 1))   // expect runtime error: Byte cannot be greater than 0xff.

test/core/string/from_byte_too_small.wren

@@ -0,0 +1 @@
+System.print(String.fromByte(-1))   // expect runtime error: Byte cannot be negative.