prusti_specs/

rewriter.rs

use crate::{
    common::HasSignature,
    specifications::{
        common::{SpecificationId, SpecificationIdGenerator},
        preparser::{parse_prusti, parse_prusti_assert_pledge, parse_prusti_pledge},
        untyped,
    },
};
use proc_macro2::{Span, TokenStream};
use quote::{format_ident, quote, quote_spanned};
use syn::{parse_quote_spanned, punctuated::Punctuated, spanned::Spanned, Pat, Token, Type};

pub(crate) struct AstRewriter {
    spec_id_generator: SpecificationIdGenerator,
}

#[derive(Clone, Debug)]
pub enum SpecItemType {
    Precondition,
    Postcondition,
    Pledge,
    Predicate(TokenStream),
    Termination,
}

impl std::fmt::Display for SpecItemType {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            SpecItemType::Precondition => write!(f, "pre"),
            SpecItemType::Postcondition => write!(f, "post"),
            SpecItemType::Pledge => write!(f, "pledge"),
            SpecItemType::Predicate(_) => write!(f, "pred"),
            SpecItemType::Termination => write!(f, "term"),
        }
    }
}

impl AstRewriter {
    pub(crate) fn new() -> Self {
        Self {
            spec_id_generator: SpecificationIdGenerator::new(),
        }
    }

    pub fn generate_spec_id(&mut self) -> SpecificationId {
        self.spec_id_generator.generate()
    }

    /// Check whether function `item` contains a parameter called `keyword`. If
    /// yes, return its span.
    fn check_contains_keyword_in_params<T: HasSignature>(
        &self,
        item: &T,
        keyword: &str,
    ) -> Option<Span> {
        for param in &item.sig().inputs {
            if let syn::FnArg::Typed(syn::PatType { pat, .. }) = param {
                if let syn::Pat::Ident(syn::PatIdent { ident, .. }) = &**pat {
                    if ident == keyword {
                        return Some(param.span());
                    }
                }
            }
        }
        None
    }

    fn generate_result_arg<T: HasSignature + Spanned>(&self, item: &T) -> syn::FnArg {
        let item_span = item.span();
        let output_ty = match &item.sig().output {
            syn::ReturnType::Default => parse_quote_spanned!(item_span=> ()),
            syn::ReturnType::Type(_, ty) => ty.clone(),
        };
        let fn_arg = syn::FnArg::Typed(syn::PatType {
            attrs: Vec::new(),
            pat: Box::new(parse_quote_spanned!(item_span=> result)),
            colon_token: syn::Token![:](item.sig().output.span()),
            ty: output_ty,
        });
        fn_arg
    }

    /// Turn an expression into the appropriate function
    pub fn generate_spec_item_fn<T: HasSignature + Spanned>(
        &mut self,
        spec_type: SpecItemType,
        spec_id: SpecificationId,
        expr: TokenStream,
        item: &T,
    ) -> syn::Result<syn::Item> {
        if let Some(span) = self.check_contains_keyword_in_params(item, "result") {
            return Err(syn::Error::new(
                span,
                "it is not allowed to use the keyword `result` as a function argument".to_string(),
            ));
        }
        let item_span = expr.span();
        let item_name = syn::Ident::new(
            &format!("prusti_{}_item_{}_{}", spec_type, item.sig().ident, spec_id),
            item_span,
        );
        let spec_id_str = spec_id.to_string();

        // about the span and expression chosen here:
        // - `item_span` is set to `expr.span()` so that any errors reported
        //   for the spec item will be reported on the span of the expression
        //   written by the user
        // - `let ...: bool = #expr` syntax is used to report type errors in the
        //   expression with the correct error message, i.e. that the expected
        //   type is `bool`, not that the expected *return* type is `bool`
        let return_type = match &spec_type {
            SpecItemType::Termination => quote_spanned! {item_span => Int},
            SpecItemType::Predicate(return_type) => return_type.clone(),
            _ => quote_spanned! {item_span => bool},
        };
        let mut spec_item: syn::ItemFn = parse_quote_spanned! {item_span=>
            #[allow(unused_must_use, unused_parens, unused_variables, dead_code, non_snake_case)]
            #[prusti::spec_only]
            #[prusti::spec_id = #spec_id_str]
            fn #item_name() -> #return_type {
                let prusti_result: #return_type = #expr;
                prusti_result
            }
        };

        spec_item.sig.generics = item.sig().generics.clone();
        spec_item.sig.inputs = item.sig().inputs.clone();
        match spec_type {
            SpecItemType::Postcondition | SpecItemType::Pledge => {
                let fn_arg = self.generate_result_arg(item);
                spec_item.sig.inputs.push(fn_arg);
            }
            _ => (),
        }
        Ok(syn::Item::Fn(spec_item))
    }

    /// Parse an assertion into a Rust expression
    pub fn process_assertion<T: HasSignature + Spanned>(
        &mut self,
        spec_type: SpecItemType,
        spec_id: SpecificationId,
        tokens: TokenStream,
        item: &T,
    ) -> syn::Result<syn::Item> {
        self.generate_spec_item_fn(spec_type, spec_id, parse_prusti(tokens)?, item)
    }

    /// Parse a pledge with lhs into a Rust expression
    pub fn process_pledge(
        &mut self,
        spec_id: SpecificationId,
        tokens: TokenStream,
        item: &untyped::AnyFnItem,
    ) -> syn::Result<syn::Item> {
        self.generate_spec_item_fn(
            SpecItemType::Pledge,
            spec_id,
            parse_prusti_pledge(tokens)?,
            item,
        )
    }

    pub fn process_pure_refinement(
        &mut self,
        spec_id: SpecificationId,
        item: &untyped::AnyFnItem,
    ) -> syn::Result<syn::Item> {
        let item_span = item.span();
        let item_name = syn::Ident::new(
            &format!("prusti_pure_ghost_item_{}", item.sig().ident),
            item_span,
        );

        let spec_id_str = spec_id.to_string();
        let mut spec_item: syn::ItemFn = parse_quote_spanned! {item_span=>
            #[allow(unused_must_use, unused_parens, unused_variables, dead_code)]
            #[prusti::spec_only]
            #[prusti::spec_id = #spec_id_str]
            fn #item_name() {} // we only need this for attaching constraints to (to evaluate when the function is pure)
        };

        spec_item.sig.generics = item.sig().generics.clone();
        spec_item.sig.inputs = item.sig().inputs.clone();
        Ok(syn::Item::Fn(spec_item))
    }

    /// Parse a pledge with lhs into a Rust expression
    pub fn process_assert_pledge(
        &mut self,
        spec_id_lhs: SpecificationId,
        spec_id_rhs: SpecificationId,
        tokens: TokenStream,
        item: &untyped::AnyFnItem,
    ) -> syn::Result<(syn::Item, syn::Item)> {
        let (lhs, rhs) = parse_prusti_assert_pledge(tokens)?;
        let lhs_item = self.generate_spec_item_fn(SpecItemType::Pledge, spec_id_lhs, lhs, item)?;
        let rhs_item = self.generate_spec_item_fn(SpecItemType::Pledge, spec_id_rhs, rhs, item)?;
        Ok((lhs_item, rhs_item))
    }

    /// Parse a loop invariant into a Rust expression
    pub fn process_loop_variant(
        &mut self,
        spec_id: SpecificationId,
        tokens: TokenStream,
    ) -> syn::Result<TokenStream> {
        let expr = parse_prusti(tokens)?;
        let spec_id_str = spec_id.to_string();
        Ok(quote_spanned! {expr.span()=>
            {
                #[prusti::spec_only]
                #[prusti::loop_body_variant_spec]
                #[prusti::spec_id = #spec_id_str]
                || -> Int {
                    #expr
                };
            }
        })
    }

    /// Parse a loop invariant into a Rust expression
    pub fn process_loop_invariant(
        &mut self,
        spec_id: SpecificationId,
        tokens: TokenStream,
    ) -> syn::Result<TokenStream> {
        self.process_prusti_expression(quote! {loop_body_invariant_spec}, spec_id, tokens)
    }

    /// Parse a prusti assertion into a Rust expression
    pub fn process_prusti_assertion(
        &mut self,
        spec_id: SpecificationId,
        tokens: TokenStream,
    ) -> syn::Result<TokenStream> {
        self.process_prusti_expression(quote! {prusti_assertion}, spec_id, tokens)
    }

    /// Parse a prusti assumption into a Rust expression
    pub fn process_prusti_assumption(
        &mut self,
        spec_id: SpecificationId,
        tokens: TokenStream,
    ) -> syn::Result<TokenStream> {
        self.process_prusti_expression(quote! {prusti_assumption}, spec_id, tokens)
    }

    /// Parse a prusti refute into a Rust expression
    pub fn process_prusti_refutation(
        &mut self,
        spec_id: SpecificationId,
        tokens: TokenStream,
    ) -> syn::Result<TokenStream> {
        self.process_prusti_expression(quote! {prusti_refutation}, spec_id, tokens)
    }

    fn process_prusti_expression(
        &mut self,
        kind: TokenStream,
        spec_id: SpecificationId,
        tokens: TokenStream,
    ) -> syn::Result<TokenStream> {
        let expr = parse_prusti(tokens)?;
        let spec_id_str = spec_id.to_string();
        Ok(quote_spanned! {expr.span()=>
            {
                #[prusti::spec_only]
                #[prusti::#kind]
                #[prusti::spec_id = #spec_id_str]
                || -> bool {
                    #expr
                };
            }
        })
    }

    /// Parse a closure with specifications into a Rust expression
    /// TODO: arguments, result (types are typically not known yet after parsing...)
    pub fn process_closure(
        &mut self,
        inputs: Punctuated<Pat, Token![,]>,
        output: Type,
        preconds: Vec<(SpecificationId, syn::Expr)>,
        postconds: Vec<(SpecificationId, syn::Expr)>,
    ) -> syn::Result<(TokenStream, TokenStream)> {
        let process_cond =
            |is_post: bool, id: &SpecificationId, assertion: &syn::Expr| -> TokenStream {
                let spec_id_str = id.to_string();
                let name = format_ident!(
                    "prusti_{}_closure_{}",
                    if is_post { "post" } else { "pre" },
                    spec_id_str
                );
                let callsite_span = Span::call_site();
                let result = if is_post && !inputs.empty_or_trailing() {
                    quote_spanned! {callsite_span=> , result: #output }
                } else if is_post {
                    quote_spanned! {callsite_span=> result: #output }
                } else {
                    TokenStream::new()
                };
                quote_spanned! {callsite_span=>
                    #[prusti::spec_only]
                    #[prusti::spec_id = #spec_id_str]
                    fn #name(#inputs #result) {
                        #assertion
                    }
                }
            };

        let mut pre_ts = TokenStream::new();
        for (id, precond) in preconds {
            pre_ts.extend(process_cond(false, &id, &precond));
        }

        let mut post_ts = TokenStream::new();
        for (id, postcond) in postconds {
            post_ts.extend(process_cond(true, &id, &postcond));
        }

        Ok((pre_ts, post_ts))
    }

    /// Parse an assertion into a Rust expression
    pub fn process_closure_assertion(
        &mut self,
        spec_id: SpecificationId,
        tokens: TokenStream,
    ) -> syn::Result<syn::Expr> {
        let expr = parse_prusti(tokens)?;
        let spec_id_str = spec_id.to_string();
        let callsite_span = Span::call_site();
        Ok(parse_quote_spanned! {callsite_span=>
            #[allow(unused_must_use, unused_variables)]
            {
                #[prusti::spec_only]
                #[prusti::spec_id = #spec_id_str]
                || -> bool {
                    #expr
                };
            }
        })
    }
}