src/test/ui-fulldeps/pprust-expr-roundtrip.rs

// run-pass
// ignore-cross-compile

// The general idea of this test is to enumerate all "interesting" expressions and check that
// `parse(print(e)) == e` for all `e`. Here's what's interesting, for the purposes of this test:
//
// 1. The test focuses on expression nesting, because interactions between different expression
//    types are harder to test manually than single expression types in isolation.
//
// 2. The test only considers expressions of at most two nontrivial nodes. So it will check `x +
//    x` and `x + (x - x)` but not `(x * x) + (x - x)`. The assumption here is that the correct
//    handling of an expression might depend on the expression's parent, but doesn't depend on its
//    siblings or any more distant ancestors.
//
// 3. The test only checks certain expression kinds. The assumption is that similar expression
//    types, such as `if` and `while` or `+` and `-`, will be handled identically in the printer
//    and parser. So if all combinations of exprs involving `if` work correctly, then combinations
//    using `while`, `if let`, and so on will likely work as well.

#![feature(rustc_private)]

extern crate rustc_data_structures;
extern crate syntax;

use rustc_data_structures::thin_vec::ThinVec;
use syntax::ast::*;
use syntax::source_map::{Spanned, DUMMY_SP, FileName};
use syntax::source_map::FilePathMapping;
use syntax::mut_visit::{self, MutVisitor, visit_clobber};
use syntax::parse::{self, ParseSess};
use syntax::print::pprust;
use syntax::ptr::P;


fn parse_expr(ps: &ParseSess, src: &str) -> Option<P<Expr>> {
    let src_as_string = src.to_string();

    let mut p = parse::new_parser_from_source_str(
        ps,
        FileName::Custom(src_as_string.clone()),
        src_as_string,
    );
    p.parse_expr().map_err(|mut e| e.cancel()).ok()
}


// Helper functions for building exprs
fn expr(kind: ExprKind) -> P<Expr> {
    P(Expr {
        id: DUMMY_NODE_ID,
        node: kind,
        span: DUMMY_SP,
        attrs: ThinVec::new(),
    })
}

fn make_x() -> P<Expr> {
    let seg = PathSegment::from_ident(Ident::from_str("x"));
    let path = Path { segments: vec![seg], span: DUMMY_SP };
    expr(ExprKind::Path(None, path))
}

/// Iterate over exprs of depth up to `depth`. The goal is to explore all "interesting"
/// combinations of expression nesting. For example, we explore combinations using `if`, but not
/// `while` or `match`, since those should print and parse in much the same way as `if`.
fn iter_exprs(depth: usize, f: &mut dyn FnMut(P<Expr>)) {
    if depth == 0 {
        f(make_x());
        return;
    }

    let mut g = |e| f(expr(e));

    for kind in 0..=19 {
        match kind {
            0 => iter_exprs(depth - 1, &mut |e| g(ExprKind::Box(e))),
            1 => iter_exprs(depth - 1, &mut |e| g(ExprKind::Call(e, vec![]))),
            2 => {
                let seg = PathSegment::from_ident(Ident::from_str("x"));
                iter_exprs(depth - 1, &mut |e| g(ExprKind::MethodCall(
                            seg.clone(), vec![e, make_x()])));
                iter_exprs(depth - 1, &mut |e| g(ExprKind::MethodCall(
                            seg.clone(), vec![make_x(), e])));
            },
            3..=8 => {
                let op = Spanned {
                    span: DUMMY_SP,
                    node: match kind {
                        3 => BinOpKind::Add,
                        4 => BinOpKind::Mul,
                        5 => BinOpKind::Shl,
                        6 => BinOpKind::And,
                        7 => BinOpKind::Or,
                        8 => BinOpKind::Lt,
                        _ => unreachable!(),
                    }
                };
                iter_exprs(depth - 1, &mut |e| g(ExprKind::Binary(op, e, make_x())));
                iter_exprs(depth - 1, &mut |e| g(ExprKind::Binary(op, make_x(), e)));
            },
            9 => {
                iter_exprs(depth - 1, &mut |e| g(ExprKind::Unary(UnOp::Deref, e)));
            },
            10 => {
                let block = P(Block {
                    stmts: Vec::new(),
                    id: DUMMY_NODE_ID,
                    rules: BlockCheckMode::Default,
                    span: DUMMY_SP,
                });
                iter_exprs(depth - 1, &mut |e| g(ExprKind::If(e, block.clone(), None)));
            },
            11 => {
                let decl = P(FnDecl {
                    inputs: vec![],
                    output: FunctionRetTy::Default(DUMMY_SP),
                    c_variadic: false,
                });
                iter_exprs(depth - 1, &mut |e| g(
                        ExprKind::Closure(CaptureBy::Value,
                                          IsAsync::NotAsync,
                                          Movability::Movable,
                                          decl.clone(),
                                          e,
                                          DUMMY_SP)));
            },
            12 => {
                iter_exprs(depth - 1, &mut |e| g(ExprKind::Assign(e, make_x())));
                iter_exprs(depth - 1, &mut |e| g(ExprKind::Assign(make_x(), e)));
            },
            13 => {
                iter_exprs(depth - 1, &mut |e| g(ExprKind::Field(e, Ident::from_str("f"))));
            },
            14 => {
                iter_exprs(depth - 1, &mut |e| g(ExprKind::Range(
                            Some(e), Some(make_x()), RangeLimits::HalfOpen)));
                iter_exprs(depth - 1, &mut |e| g(ExprKind::Range(
                            Some(make_x()), Some(e), RangeLimits::HalfOpen)));
            },
            15 => {
                iter_exprs(depth - 1, &mut |e| g(ExprKind::AddrOf(Mutability::Immutable, e)));
            },
            16 => {
                g(ExprKind::Ret(None));
                iter_exprs(depth - 1, &mut |e| g(ExprKind::Ret(Some(e))));
            },
            17 => {
                let path = Path::from_ident(Ident::from_str("S"));
                g(ExprKind::Struct(path, vec![], Some(make_x())));
            },
            18 => {
                iter_exprs(depth - 1, &mut |e| g(ExprKind::Try(e)));
            },
            19 => {
                let pat = P(Pat {
                    id: DUMMY_NODE_ID,
                    node: PatKind::Wild,
                    span: DUMMY_SP,
                });
                iter_exprs(depth - 1, &mut |e| g(ExprKind::Let(pat.clone(), e)))
            },
            _ => panic!("bad counter value in iter_exprs"),
        }
    }
}


// Folders for manipulating the placement of `Paren` nodes. See below for why this is needed.

/// `MutVisitor` that removes all `ExprKind::Paren` nodes.
struct RemoveParens;

impl MutVisitor for RemoveParens {
    fn visit_expr(&mut self, e: &mut P<Expr>) {
        match e.node.clone() {
            ExprKind::Paren(inner) => *e = inner,
            _ => {}
        };
        mut_visit::noop_visit_expr(e, self);
    }
}


/// `MutVisitor` that inserts `ExprKind::Paren` nodes around every `Expr`.
struct AddParens;

impl MutVisitor for AddParens {
    fn visit_expr(&mut self, e: &mut P<Expr>) {
        mut_visit::noop_visit_expr(e, self);
        visit_clobber(e, |e| {
            P(Expr {
                id: DUMMY_NODE_ID,
                node: ExprKind::Paren(e),
                span: DUMMY_SP,
                attrs: ThinVec::new(),
            })
        });
    }
}

fn main() {
    syntax::with_default_globals(|| run());
}

fn run() {
    let ps = ParseSess::new(FilePathMapping::empty());

    iter_exprs(2, &mut |mut e| {
        // If the pretty printer is correct, then `parse(print(e))` should be identical to `e`,
        // modulo placement of `Paren` nodes.
        let printed = pprust::expr_to_string(&e);
        println!("printed: {}", printed);

        // Ignore expressions with chained comparisons that fail to parse
        if let Some(mut parsed) = parse_expr(&ps, &printed) {
            // We want to know if `parsed` is structurally identical to `e`, ignoring trivial
            // differences like placement of `Paren`s or the exact ranges of node spans.
            // Unfortunately, there is no easy way to make this comparison. Instead, we add `Paren`s
            // everywhere we can, then pretty-print. This should give an unambiguous representation
            // of each `Expr`, and it bypasses nearly all of the parenthesization logic, so we
            // aren't relying on the correctness of the very thing we're testing.
            RemoveParens.visit_expr(&mut e);
            AddParens.visit_expr(&mut e);
            let text1 = pprust::expr_to_string(&e);
            RemoveParens.visit_expr(&mut parsed);
            AddParens.visit_expr(&mut parsed);
            let text2 = pprust::expr_to_string(&parsed);
            assert!(text1 == text2,
                    "exprs are not equal:\n  e =      {:?}\n  parsed = {:?}",
                    text1, text2);
        }
    });
}