| use std::convert::TryFrom; |
| |
| use proc_macro2::TokenStream; |
| use quote::ToTokens; |
| use syn::{self, spanned::Spanned, Block, LitStr}; |
| |
| /// A wrapper for expressions/blocks which automatically adds the start and end |
| /// braces. |
| /// |
| /// - **full access** to variables environment. |
| /// - **full access** to control-flow of the environment via `return`, `?` etc. |
| /// ``` |
| #[derive(Debug, Clone)] |
| pub struct BlockContents(Block); |
| |
| impl BlockContents { |
| pub fn is_empty(&self) -> bool { |
| self.0.stmts.is_empty() |
| } |
| } |
| |
| impl ToTokens for BlockContents { |
| fn to_tokens(&self, tokens: &mut TokenStream) { |
| self.0.to_tokens(tokens) |
| } |
| } |
| |
| impl TryFrom<&'_ LitStr> for BlockContents { |
| type Error = syn::Error; |
| |
| fn try_from(s: &LitStr) -> Result<Self, Self::Error> { |
| let mut block_str = s.value(); |
| block_str.insert(0, '{'); |
| block_str.push('}'); |
| LitStr::new(&block_str, s.span()).parse().map(Self) |
| } |
| } |
| |
| impl From<syn::Expr> for BlockContents { |
| fn from(v: syn::Expr) -> Self { |
| Self(Block { |
| brace_token: syn::token::Brace(v.span()), |
| stmts: vec![syn::Stmt::Expr(v)], |
| }) |
| } |
| } |
| |
| #[cfg(test)] |
| mod test { |
| use std::convert::TryInto; |
| |
| use super::*; |
| use proc_macro2::Span; |
| |
| fn parse(s: &str) -> Result<BlockContents, syn::Error> { |
| (&LitStr::new(s, Span::call_site())).try_into() |
| } |
| |
| #[test] |
| #[should_panic(expected = r#"lex error"#)] |
| fn block_invalid_token_trees() { |
| parse("let x = 2; { x+1").unwrap(); |
| } |
| |
| #[test] |
| fn block_delimited_token_tree() { |
| let expr = parse("let x = 2; { x+1 }").unwrap(); |
| assert_eq!( |
| quote!(#expr).to_string(), |
| quote!({ |
| let x = 2; |
| { |
| x + 1 |
| } |
| }) |
| .to_string() |
| ); |
| } |
| |
| #[test] |
| fn block_single_token_tree() { |
| let expr = parse("42").unwrap(); |
| assert_eq!(quote!(#expr).to_string(), quote!({ 42 }).to_string()); |
| } |
| } |