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Diffstat (limited to '')
| -rw-r--r-- | askama_derive/src/parser.rs | 33 |
1 files changed, 33 insertions, 0 deletions
diff --git a/askama_derive/src/parser.rs b/askama_derive/src/parser.rs index efcad73..dc163fa 100644 --- a/askama_derive/src/parser.rs +++ b/askama_derive/src/parser.rs @@ -106,6 +106,39 @@ impl Expr<'_> { _ => false, } } + + /// Returns `true` if the outcome of this expression may be used multiple times in the same + /// `write!()` call, without evaluating the expression again, i.e. the expression should be + /// side-effect free. + pub(crate) fn is_cachable(&self) -> bool { + match self { + // Literals are the definition of pure: + Expr::BoolLit(_) => true, + Expr::NumLit(_) => true, + Expr::StrLit(_) => true, + Expr::CharLit(_) => true, + // fmt::Display should have no effects: + Expr::Var(_) => true, + Expr::Path(_) => true, + // Check recursively: + Expr::Array(args) => args.iter().all(|arg| arg.is_cachable()), + Expr::Attr(lhs, _) => lhs.is_cachable(), + Expr::Index(lhs, rhs) => lhs.is_cachable() && rhs.is_cachable(), + Expr::Filter(_, args) => args.iter().all(|arg| arg.is_cachable()), + Expr::Unary(_, arg) => arg.is_cachable(), + Expr::BinOp(_, lhs, rhs) => lhs.is_cachable() && rhs.is_cachable(), + Expr::Range(_, lhs, rhs) => { + lhs.as_ref().map_or(true, |v| v.is_cachable()) + && rhs.as_ref().map_or(true, |v| v.is_cachable()) + } + Expr::Group(arg) => arg.is_cachable(), + Expr::Tuple(args) => args.iter().all(|arg| arg.is_cachable()), + // We have too little information to tell if the expression is pure: + Expr::Call(_, _) => false, + Expr::RustMacro(_, _) => false, + Expr::Try(_) => false, + } + } } pub(crate) type When<'a> = (Ws, Target<'a>, Vec<Node<'a>>); |