multiboot2: make FramebufferTypeId used again

multiboot2/src/framebuffer.rs

@@ -104,8 +104,9 @@ impl FramebufferTag {
     /// The type of framebuffer, one of: `Indexed`, `RGB` or `Text`.
     pub fn buffer_type(&self) -> Result<FramebufferType, UnknownFramebufferType> {
         let mut reader = Reader::new(self.buffer.as_ptr());
-        match self.type_no {
-            0 => {
+        let typ = FramebufferTypeId::try_from(self.type_no)?;
+        match typ {
+            FramebufferTypeId::Indexed => {
                 let num_colors = reader.read_u32();
                 let palette = unsafe {
                     slice::from_raw_parts(
@@ -115,7 +116,7 @@ impl FramebufferTag {
                 } as &'static [FramebufferColor];
                 Ok(FramebufferType::Indexed { palette })
             }
-            1 => {
+            FramebufferTypeId::RGB => {
                 let red_pos = reader.read_u8(); // These refer to the bit positions of the LSB of each field
                 let red_mask = reader.read_u8(); // And then the length of the field from LSB to MSB
                 let green_pos = reader.read_u8();
@@ -137,8 +138,7 @@ impl FramebufferTag {
                     },
                 })
             }
-            2 => Ok(FramebufferType::Text),
-            no => Err(UnknownFramebufferType(no)),
+            FramebufferTypeId::Text => Ok(FramebufferType::Text),
         }
     }
 }
@@ -187,16 +187,29 @@ impl PartialEq for FramebufferTag {
 }
 
 /// Helper struct for [`FramebufferType`].
-#[derive(Debug, PartialEq, Eq)]
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
 #[repr(u8)]
 #[allow(clippy::upper_case_acronyms)]
-pub enum FramebufferTypeId {
+enum FramebufferTypeId {
     Indexed = 0,
     RGB = 1,
     Text = 2,
     // spec says: there may be more variants in the future
 }
 
+impl TryFrom<u8> for FramebufferTypeId {
+    type Error = UnknownFramebufferType;
+
+    fn try_from(value: u8) -> Result<Self, Self::Error> {
+        match value {
+            0 => Ok(Self::Indexed),
+            1 => Ok(Self::RGB),
+            2 => Ok(Self::Text),
+            val => Err(UnknownFramebufferType(val))
+        }
+    }
+}
+
 /// The type of framebuffer.
 #[derive(Debug, PartialEq, Eq)]
 pub enum FramebufferType<'a> {
@@ -224,8 +237,8 @@ pub enum FramebufferType<'a> {
     Text,
 }
 
+#[cfg(feature = "builder")]
 impl<'a> FramebufferType<'a> {
-    #[cfg(feature = "builder")]
     fn to_bytes(&self) -> Vec<u8> {
         let mut v = Vec::new();
         match self {