Add FromMeta for Vec of literals(#265)

There is no general implementation for `Vec`, but having the ability to accept a list of literals
and require that they be of the same type is useful enough to merit specific impls.

Co-authored-by: Ted Driggs <ted.driggs@outlook.com>

core/src/from_meta.rs

@@ -516,6 +516,33 @@ macro_rules! from_meta_lit {
                 }
             }
         }
+
+        impl FromMeta for Vec<$impl_ty> {
+            fn from_list(items: &[NestedMeta]) -> Result<Self> {
+                items
+                    .iter()
+                    .map(<$impl_ty as FromMeta>::from_nested_meta)
+                    .collect()
+            }
+
+            fn from_value(value: &syn::Lit) -> Result<Self> {
+                let expr_array = syn::ExprArray::from_value(value)?;
+                Self::from_expr(&syn::Expr::Array(expr_array))
+            }
+
+            fn from_expr(expr: &syn::Expr) -> Result<Self> {
+                match expr {
+                    syn::Expr::Array(expr_array) => expr_array
+                        .elems
+                        .iter()
+                        .map(<$impl_ty as FromMeta>::from_expr)
+                        .collect::<Result<Vec<_>>>(),
+                    syn::Expr::Lit(expr_lit) => Self::from_value(&expr_lit.lit),
+                    syn::Expr::Group(g) => Self::from_expr(&g.expr),
+                    _ => Err(Error::unexpected_expr_type(expr)),
+                }
+            }
+        }
     };
 }
 
@@ -1044,4 +1071,15 @@ mod tests {
             vec![0x50, 0xffffffff]
         );
     }
+
+    #[test]
+    fn test_lit_array() {
+        fm::<Vec<syn::LitStr>>(quote!(ignore = "[\"Hello World\", \"Test Array\"]"));
+        fm::<Vec<syn::LitStr>>(quote!(ignore = ["Hello World", "Test Array"]));
+        fm::<Vec<syn::LitChar>>(quote!(ignore = "['a', 'b', 'c']"));
+        fm::<Vec<syn::LitBool>>(quote!(ignore = "[true]"));
+        fm::<Vec<syn::LitStr>>(quote!(ignore = "[]"));
+        fm::<Vec<syn::LitStr>>(quote!(ignore = []));
+        fm::<Vec<syn::LitBool>>(quote!(ignore = [true, false]));
+    }
 }