feat(fstring): add sign-aware alignment

examples/basic/23_format_spec.peb

@@ -55,5 +55,12 @@ print(f"{"test":<<9}")
 print(f"{"test":>>9}")
 print(f"{"test":^^9}")
 print()
+print(f"{d2:8}")
+print(f"{d2:08}")
+print(f"{d2:<<8}")
+print(f"{d2:>>8}")
+print(f"{d2:^^8}")
+print(f"{d2:==8}")
+print()
 
 print("Complex")

src/core/format_spec/lexer.py

@@ -83,6 +83,8 @@ class FormatSpecLexer:
                 self.add_token(TokenType.RIGHT)
             case "^":
                 self.add_token(TokenType.CENTER)
+            case "=":
+                self.add_token(TokenType.EQUAL)
             case "+":
                 self.add_token(TokenType.PLUS)
             case "-":
@@ -113,6 +115,8 @@ class FormatSpecLexer:
                 self.add_token(TokenType.T_PCT)
             case ".":
                 self.add_token(TokenType.DOT)
+            case "0":
+                self.add_token(TokenType.ZERO)
             case _:
                 if char.isdigit():
                     self.scan_number()

src/core/format_spec/parser.py

@@ -23,13 +23,14 @@ class FormatSpecParser:
     ALIGNMENT: set[TokenType] = {
         TokenType.LEFT,
         TokenType.RIGHT,
-        TokenType.CENTER
+        TokenType.CENTER,
+        TokenType.EQUAL,
     }
 
     SIGN: set[TokenType] = {
         TokenType.PLUS,
         TokenType.MINUS,
-        TokenType.SPACE
+        TokenType.SPACE,
     }
 
     def __init__(self, tokens: list[Token]):
@@ -93,9 +94,12 @@ class FormatSpecParser:
         if self.match(*self.SIGN):
             sign = self.previous()
 
+        zfill: bool = self.match(TokenType.ZERO)
+
         return FormatSpecOptions(
             alignment=alignment,
-            sign=sign
+            sign=sign,
+            zfill=zfill
         )
 
     def alignment(self) -> Optional[FormatSpecAlignment]:

src/core/format_spec/spec.py

@@ -14,6 +14,7 @@ class FormatSpecAlignment:
 class FormatSpecOptions:
     alignment: Optional[FormatSpecAlignment]
     sign: Optional[Token]
+    zfill: bool
 
 
 @dataclass(frozen=True)

src/core/format_spec/string_formatter.py

@@ -69,8 +69,7 @@ class StringFormatter:
         else:
             fmt_type, obj = self.guess_type(obj)
 
-        align_side: TokenType = TokenType.LEFT
-        fill_char: str = " "
+        is_num: bool = False
         match fmt_type:
             case None:
                 res = self.stringify(obj)
@@ -78,18 +77,27 @@ class StringFormatter:
                 res = obj
             case TokenType.T_BIN | TokenType.T_DEC | TokenType.T_HEX | TokenType.T_HEX_CAPS | TokenType.T_OCT:
                 res = self.format_int(obj, spec, fmt_type)
-                align_side = TokenType.RIGHT
+                is_num = True
             case TokenType.T_FIX:
                 res = self.format_float_fix(obj, spec, fmt_type)
-                align_side = TokenType.RIGHT
+                is_num = True
             case TokenType.T_PCT:
                 res = self.format_float_fix(obj * 100, spec, TokenType.T_FIX) + "%"
-                align_side = TokenType.RIGHT
+                is_num = True
             case TokenType.T_SCI:
                 res = self.format_float_sci(obj, spec, fmt_type)
-                align_side = TokenType.RIGHT
+                is_num = True
 
         align_spec: Optional[FormatSpecAlignment] = spec.options.alignment
+        align_side: TokenType = TokenType.LEFT
+        fill_char: str = "0" if spec.options.zfill else " "
+        if is_num:
+            align_side = TokenType.EQUAL if spec.options.zfill else TokenType.RIGHT
+        elif align_side == TokenType.EQUAL:
+            # Should always be true at this point
+            if align_spec is not None:
+                raise PebbleRuntimeError(align_spec.align, "Sign-aware alignment is only valid for numbers.")
+
         if align_spec is not None:
             align_side = align_spec.align.type
             if align_spec.fill is not None:
@@ -190,11 +198,16 @@ class StringFormatter:
             case TokenType.LEFT:
                 left = 0
                 right = to_pad
-            case TokenType.RIGHT:
+            case TokenType.RIGHT | TokenType.EQUAL:
                 left = to_pad
                 right = 0
             case TokenType.CENTER:
                 left = to_pad // 2
                 right = to_pad - left
 
-        return char * left + string + char * right
+        sign: str = ""
+        if side == TokenType.EQUAL:
+            if string.startswith(("+", "-", " ")):
+                sign = string[0]
+                string = string[1:]
+        return sign + char * left + string + char * right

src/core/format_spec/token.py

@@ -10,6 +10,7 @@ class TokenType(Enum):
     LEFT = auto()
     RIGHT = auto()
     CENTER = auto()
+    EQUAL = auto()
 
     # Sign
     PLUS = auto()
@@ -37,6 +38,7 @@ class TokenType(Enum):
     T_PCT = auto()
 
     # Misc
+    ZERO = auto()
     NUMBER = auto()
     DOT = auto()
     EOF = auto()