Implement FromStr for TerrainMaterials (#354)

Closes #353.

This also modifies `MaterialColorsError` to be a generalized error for
both `MaterialColors` and `TerrainColors`. This is technically a
breaking change because the enum is publicly exposed, but I don't think
it will seriously impact anyone beyond adding a new variant to the enum.

rbx_types/CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## Unreleased Changes
 
+* Implement `FromStr` for `TerrainMaterials`. ([#354])
+
+[#354]: https://github.com/rojo-rbx/rbx-dom/pull/354
+
 ## 1.6.0 (2023-08-09)
 * Added support for `UniqueId` values. ([#271])
 * Changed `BinaryString`'s non-human readable serde implementation to be identical to `Vec<u8>`. ([#276])

rbx_types/src/material_colors.rs

@@ -1,4 +1,4 @@
-use std::collections::BTreeMap;
+use std::{collections::BTreeMap, str::FromStr};
 
 use thiserror::Error;
 
@@ -88,14 +88,18 @@ where
     }
 }
 
-/// An error that can occur when deserializing MaterialColors.
+/// An error that can occur when deserializing or working with MaterialColors and TerrainMaterials.
 #[derive(Debug, Error)]
 pub enum MaterialColorsError {
     /// The `MaterialColors` blob was the wrong number of bytes.
     #[error(
         "MaterialColors blob was the wrong length (expected it to be 69 bytes, it was {0} bytes)"
     )]
     WrongLength(usize),
+    /// The argument provided to `from_str` did not correspond to a known
+    /// TerrainMaterial.
+    #[error("cannot convert `{0}` into TerrainMaterial")]
+    UnknownMaterial(String),
 }
 
 /// Constructs an enum named `TerrainMaterials` for all values contained in
@@ -136,6 +140,18 @@ macro_rules! material_colors {
                 }
             }
         }
+
+        impl FromStr for TerrainMaterials {
+            type Err = CrateError;
+
+            fn from_str(s: &str) -> Result<Self, Self::Err> {
+                match s {$(
+                    stringify!($name) => Ok(Self::$name),
+                )*
+                    _ => Err(MaterialColorsError::UnknownMaterial(s.to_string()).into()),
+                }
+            }
+        }
     };
 }
 
@@ -265,4 +281,18 @@ mod test {
 
         assert_eq!(blob, "AAAAAAAAAQIDBAUGBwgJCgsMDQ4PEBESExQVFhcYGRobHB0eHyAhIiMkJSYnKCkqKywtLi8wMTIzNDU2Nzg5Ojs8PT4/");
     }
+
+    #[test]
+    fn from_str_materials() {
+        assert!(TerrainMaterials::from_str("Grass").is_ok());
+        assert!(TerrainMaterials::from_str("Concrete").is_ok());
+        assert!(TerrainMaterials::from_str("Rock").is_ok());
+        assert!(TerrainMaterials::from_str("Asphalt").is_ok());
+        assert!(TerrainMaterials::from_str("Salt").is_ok());
+        assert!(TerrainMaterials::from_str("Pavement").is_ok());
+
+        assert!(TerrainMaterials::from_str("A name I am certain Roblox will never add").is_err());
+        // `from_str` is case-sensitive
+        assert!(TerrainMaterials::from_str("gRaSs").is_err());
+    }
 }