formatting_options: Make all methods const

Having `const fn`s that take a `mut &` was unstable until Rust 1.83. Because of
this, not all methods on `FormattingOptions` were implemented as `const`. As
this has been stabilized now, there is no reason not to have all methods
`const`.
Thanks to Ternvein for bringing this to my attention (see [1]).
[1]: #118117 (comment)

Author: EliasHolzmann

library/core/src/fmt/mod.rs

@@ -359,7 +359,7 @@ impl FormattingOptions {
 /// always be printed.
 /// - `-`: Currently not used
 #[unstable(feature = "formatting_options", issue = "118117")]
-pubfnsign(&mutself,sign:Option<Sign>) -> &mutSelf{
+pubconstfnsign(&mutself,sign:Option<Sign>) -> &mutSelf{
 let sign = match sign {
 None => 0,
 Some(Sign::Plus) => flags::SIGN_PLUS_FLAG,
@@ -372,7 +372,7 @@ impl FormattingOptions {
 ///
 /// This is used to indicate for integer formats that the padding to width should both be done with a 0 character as well as be sign-aware
 #[unstable(feature = "formatting_options", issue = "118117")]
-pubfnsign_aware_zero_pad(&mutself,sign_aware_zero_pad:bool) -> &mutSelf{
+pubconstfnsign_aware_zero_pad(&mutself,sign_aware_zero_pad:bool) -> &mutSelf{
 if sign_aware_zero_pad {
 self.flags |= flags::SIGN_AWARE_ZERO_PAD_FLAG;
 }else{
@@ -389,7 +389,7 @@ impl FormattingOptions {
 /// - [`Octal`] - precedes the argument with a `0b`
 /// - [`Binary`] - precedes the argument with a `0o`
 #[unstable(feature = "formatting_options", issue = "118117")]
-pubfnalternate(&mutself,alternate:bool) -> &mutSelf{
+pubconstfnalternate(&mutself,alternate:bool) -> &mutSelf{
 if alternate {
 self.flags |= flags::ALTERNATE_FLAG;
 }else{
@@ -404,7 +404,7 @@ impl FormattingOptions {
 /// being formatted is smaller than width some extra characters will be
 /// printed around it.
 #[unstable(feature = "formatting_options", issue = "118117")]
-pubfnfill(&mutself,fill:char) -> &mutSelf{
+pubconstfnfill(&mutself,fill:char) -> &mutSelf{
 self.flags = self.flags&(u32::MAX << 21) | fill asu32;
 self
 }
@@ -413,7 +413,7 @@ impl FormattingOptions {
 /// The alignment specifies how the value being formatted should be
 /// positioned if it is smaller than the width of the formatter.
 #[unstable(feature = "formatting_options", issue = "118117")]
-pubfnalign(&mutself,align:Option<Alignment>) -> &mutSelf{
+pubconstfnalign(&mutself,align:Option<Alignment>) -> &mutSelf{
 let align:u32 = match align {
 Some(Alignment::Left) => flags::ALIGN_LEFT,
 Some(Alignment::Right) => flags::ALIGN_RIGHT,
@@ -430,7 +430,7 @@ impl FormattingOptions {
 /// the padding specified by [`FormattingOptions::fill`]/[`FormattingOptions::align`]
 /// will be used to take up the required space.
 #[unstable(feature = "formatting_options", issue = "118117")]
-pubfnwidth(&mutself,width:Option<u16>) -> &mutSelf{
+pubconstfnwidth(&mutself,width:Option<u16>) -> &mutSelf{
 ifletSome(width) = width {
 self.flags |= flags::WIDTH_FLAG;
 self.width = width;
@@ -450,7 +450,7 @@ impl FormattingOptions {
 /// - For floating-point types, this indicates how many digits after the
 /// decimal point should be printed.
 #[unstable(feature = "formatting_options", issue = "118117")]
-pubfnprecision(&mutself,precision:Option<u16>) -> &mutSelf{
+pubconstfnprecision(&mutself,precision:Option<u16>) -> &mutSelf{
 ifletSome(precision) = precision {
 self.flags |= flags::PRECISION_FLAG;
 self.precision = precision;
@@ -463,7 +463,7 @@ impl FormattingOptions {
 /// Specifies whether the [`Debug`] trait should use lower-/upper-case
 /// hexadecimal or normal integers
 #[unstable(feature = "formatting_options", issue = "118117")]
-pubfndebug_as_hex(&mutself,debug_as_hex:Option<DebugAsHex>) -> &mutSelf{
+pubconstfndebug_as_hex(&mutself,debug_as_hex:Option<DebugAsHex>) -> &mutSelf{
 let debug_as_hex = match debug_as_hex {
 None => 0,
 Some(DebugAsHex::Lower) => flags::DEBUG_LOWER_HEX_FLAG,
@@ -537,7 +537,7 @@ impl FormattingOptions {
 ///
 /// You may alternatively use [`Formatter::new()`].
 #[unstable(feature = "formatting_options", issue = "118117")]
-pubfncreate_formatter<'a>(self,write:&'amut(dynWrite + 'a)) -> Formatter<'a>{
+pubconstfncreate_formatter<'a>(self,write:&'amut(dynWrite + 'a)) -> Formatter<'a>{
 Formatter{options:self,buf: write }
 }
 }
@@ -578,13 +578,13 @@ impl<'a> Formatter<'a> {
 ///
 /// You may alternatively use [`FormattingOptions::create_formatter()`].
 #[unstable(feature = "formatting_options", issue = "118117")]
-pubfnnew(write:&'amut(dynWrite + 'a),options:FormattingOptions) -> Self{
+pubconstfnnew(write:&'amut(dynWrite + 'a),options:FormattingOptions) -> Self{
 Formatter{ options,buf: write }
 }
 
 /// Creates a new formatter based on this one with given [`FormattingOptions`].
 #[unstable(feature = "formatting_options", issue = "118117")]
-pubfnwith_options<'b>(&'bmutself,options:FormattingOptions) -> Formatter<'b>{
+pubconstfnwith_options<'b>(&'bmutself,options:FormattingOptions) -> Formatter<'b>{
 Formatter{ options,buf:self.buf}
 }
 }