diff --git a/tests/ui-fulldeps/pprust-parenthesis-insertion.rs b/tests/ui-fulldeps/pprust-parenthesis-insertion.rs new file mode 100644 index 0000000000000..fd6644d73c161 --- /dev/null +++ b/tests/ui-fulldeps/pprust-parenthesis-insertion.rs @@ -0,0 +1,242 @@ +//@ run-pass +//@ ignore-cross-compile + +// This test covers the AST pretty-printer's automatic insertion of parentheses +// into unparenthesized syntax trees according to precedence and various grammar +// restrictions and edge cases. +// +// For example if the following syntax tree represents the expression a*(b+c), +// in which the parenthesis is necessary for precedence: +// +// Binary('*', Path("a"), Paren(Binary('+', Path("b"), Path("c")))) +// +// then the pretty-printer needs to be able to print the following +// unparenthesized syntax tree with an automatically inserted parenthesization. +// +// Binary('*', Path("a"), Binary('+', Path("b"), Path("c"))) +// +// Handling this correctly is relevant in real-world code when pretty-printing +// macro-generated syntax trees, in which expressions can get interpolated into +// one another without any parenthesization being visible in the syntax tree. +// +// macro_rules! repro { +// ($rhs:expr) => { +// a * $rhs +// }; +// } +// +// let _ = repro!(b + c); + +#![feature(rustc_private)] + +extern crate rustc_ast; +extern crate rustc_ast_pretty; +extern crate rustc_driver; +extern crate rustc_errors; +extern crate rustc_parse; +extern crate rustc_session; +extern crate rustc_span; +extern crate smallvec; + +use std::mem; +use std::process::ExitCode; + +use rustc_ast::ast::{DUMMY_NODE_ID, Expr, ExprKind, Stmt}; +use rustc_ast::mut_visit::{self, DummyAstNode as _, MutVisitor}; +use rustc_ast::node_id::NodeId; +use rustc_ast::ptr::P; +use rustc_ast_pretty::pprust; +use rustc_errors::Diag; +use rustc_parse::parser::Recovery; +use rustc_session::parse::ParseSess; +use rustc_span::{DUMMY_SP, FileName, Span}; +use smallvec::SmallVec; + +// Every parenthesis in the following expressions is re-inserted by the +// pretty-printer. +// +// FIXME: Some of them shouldn't be. +static EXPRS: &[&str] = &[ + // Straightforward binary operator precedence. + "2 * 2 + 2", + "2 + 2 * 2", + "(2 + 2) * 2", + "2 * (2 + 2)", + "2 + 2 + 2", + // Return has lower precedence than a binary operator. + "(return 2) + 2", + "2 + (return 2)", // FIXME: no parenthesis needed. + "(return) + 2", // FIXME: no parenthesis needed. + // These mean different things. + "return - 2", + "(return) - 2", + // These mean different things. + "if let _ = true && false {}", + "if let _ = (true && false) {}", + // Conditions end at the first curly brace, so struct expressions need to be + // parenthesized. Except in a match guard, where conditions end at arrow. + "if let _ = (Struct {}) {}", + "match 2 { _ if let _ = Struct {} => {} }", + // Match arms terminate eagerly, so parenthesization is needed around some + // expressions. + "match 2 { _ => 1 - 1 }", + "match 2 { _ => ({ 1 }) - 1 }", + // Grammar restriction: break value starting with a labeled loop is not + // allowed, except if the break is also labeled. + "break 'outer 'inner: loop {} + 2", + "break ('inner: loop {} + 2)", + // Grammar restriction: the value in let-else is not allowed to end in a + // curly brace. + "{ let _ = 1 + 1 else {}; }", + "{ let _ = (loop {}) else {}; }", + "{ let _ = mac!() else {}; }", + "{ let _ = (mac! {}) else {}; }", + // Parentheses are necessary to prevent an eager statement boundary. + "{ 2 - 1 }", + "{ (match 2 {}) - 1 }", + "{ (match 2 {})() - 1 }", + "{ (match 2 {})[0] - 1 }", + "{ (loop {}) - 1 }", + // Angle bracket is eagerly parsed as a path's generic argument list. + "(2 as T) < U", + "(2 as T) < V", // FIXME: no parentheses needed. + /* + // FIXME: pretty-printer produces invalid syntax. `2 + 2 as T < U` + "(2 + 2 as T) < U", + */ + /* + // FIXME: pretty-printer produces invalid syntax. `if (let _ = () && Struct {}.x) {}` + "if let _ = () && (Struct {}).x {}", + */ + /* + // FIXME: pretty-printer produces invalid syntax. `(1 < 2 == false) as usize` + "((1 < 2) == false) as usize", + */ + /* + // FIXME: pretty-printer produces invalid syntax. `for _ in 1..{ 2 } {}` + "for _ in (1..{ 2 }) {}", + */ + /* + // FIXME: pretty-printer loses the attribute. `{ let Struct { field } = s; }` + "{ let Struct { #[attr] field } = s; }", + */ + /* + // FIXME: pretty-printer turns this into a range. `0..to_string()` + "(0.).to_string()", + "0. .. 1.", + */ + /* + // FIXME: pretty-printer loses the dyn*. `i as Trait` + "i as dyn* Trait", + */ +]; + +// Flatten the content of parenthesis nodes into their parent node. For example +// this syntax tree representing the expression a*(b+c): +// +// Binary('*', Path("a"), Paren(Binary('+', Path("b"), Path("c")))) +// +// would unparenthesize to: +// +// Binary('*', Path("a"), Binary('+', Path("b"), Path("c"))) +struct Unparenthesize; + +impl MutVisitor for Unparenthesize { + fn visit_expr(&mut self, e: &mut P) { + while let ExprKind::Paren(paren) = &mut e.kind { + **e = mem::replace(&mut *paren, Expr::dummy()); + } + mut_visit::walk_expr(self, e); + } +} + +// Erase Span information that could distinguish between identical expressions +// parsed from different source strings. +struct Normalize; + +impl MutVisitor for Normalize { + const VISIT_TOKENS: bool = true; + + fn visit_id(&mut self, id: &mut NodeId) { + *id = DUMMY_NODE_ID; + } + + fn visit_span(&mut self, span: &mut Span) { + *span = DUMMY_SP; + } + + fn visit_expr(&mut self, expr: &mut P) { + if let ExprKind::Binary(binop, _left, _right) = &mut expr.kind { + self.visit_span(&mut binop.span); + } + mut_visit::walk_expr(self, expr); + } + + fn flat_map_stmt(&mut self, mut stmt: Stmt) -> SmallVec<[Stmt; 1]> { + self.visit_span(&mut stmt.span); + mut_visit::walk_flat_map_stmt(self, stmt) + } +} + +fn parse_expr(psess: &ParseSess, source_code: &str) -> Option> { + let parser = rustc_parse::unwrap_or_emit_fatal(rustc_parse::new_parser_from_source_str( + psess, + FileName::anon_source_code(source_code), + source_code.to_owned(), + )); + + let mut expr = parser.recovery(Recovery::Forbidden).parse_expr().map_err(Diag::cancel).ok()?; + Normalize.visit_expr(&mut expr); + Some(expr) +} + +fn main() -> ExitCode { + let mut status = ExitCode::SUCCESS; + let mut fail = |description: &str, before: &str, after: &str| { + status = ExitCode::FAILURE; + eprint!( + "{description}\n BEFORE: {before}\n AFTER: {after}\n\n", + before = before.replace('\n', "\n "), + after = after.replace('\n', "\n "), + ); + }; + + rustc_span::create_default_session_globals_then(|| { + let psess = &ParseSess::new(vec![rustc_parse::DEFAULT_LOCALE_RESOURCE]); + + for &source_code in EXPRS { + let expr = parse_expr(psess, source_code).unwrap(); + + // Check for FALSE POSITIVE: pretty-printer inserting parentheses where not needed. + // Pseudocode: + // assert(expr == parse(print(expr))) + let printed = &pprust::expr_to_string(&expr); + let Some(expr2) = parse_expr(psess, printed) else { + fail("Pretty-printer produced invalid syntax", source_code, printed); + continue; + }; + if format!("{expr:#?}") != format!("{expr2:#?}") { + fail("Pretty-printer inserted unnecessary parenthesis", source_code, printed); + continue; + } + + // Check for FALSE NEGATIVE: pretty-printer failing to place necessary parentheses. + // Pseudocode: + // assert(unparenthesize(expr) == unparenthesize(parse(print(unparenthesize(expr))))) + let mut expr = expr; + Unparenthesize.visit_expr(&mut expr); + let printed = &pprust::expr_to_string(&expr); + let Some(mut expr2) = parse_expr(psess, printed) else { + fail("Pretty-printer with no parens produced invalid syntax", source_code, printed); + continue; + }; + Unparenthesize.visit_expr(&mut expr2); + if format!("{expr:#?}") != format!("{expr2:#?}") { + fail("Pretty-printer lost necessary parentheses", source_code, printed); + continue; + } + } + }); + + status +}