[RFC 2011] Minimal initial implementation

compiler/rustc_builtin_macros/src/assert/context.rs

@@ -1,44 +1,299 @@
-use rustc_ast::{ptr::P, Expr, Path};
+use crate::assert::expr_if_not;
+use rustc_ast::{
+    attr,
+    ptr::P,
+    token,
+    tokenstream::{DelimSpan, TokenStream, TokenTree},
+    BorrowKind, Expr, ExprKind, ItemKind, MacArgs, MacCall, MacDelimiter, Mutability, Path,
+    PathSegment, Stmt, UseTree, UseTreeKind, DUMMY_NODE_ID,
+};
+use rustc_ast_pretty::pprust;
+use rustc_data_structures::fx::FxHashSet;
 use rustc_expand::base::ExtCtxt;
-use rustc_span::Span;
+use rustc_span::{
+    symbol::{sym, Ident, Symbol},
+    Span,
+};
 
 pub(super) struct Context<'cx, 'a> {
+    // Top-level `let captureN = Capture::new()` statements
+    capture_decls: Vec<Capture>,
     cx: &'cx ExtCtxt<'a>,
+    // Formatting string used for debugging
+    fmt_string: String,
+    // Top-level `let __local_bindN = &expr` statements
+    local_bind_decls: Vec<Stmt>,
+    // Used to avoid capturing duplicated paths
+    //
+    // ```rust
+    // let a = 1i32;
+    // assert!(add(a, a) == 3);
+    // ```
+    paths: FxHashSet<Ident>,
     span: Span,
 }
 
 impl<'cx, 'a> Context<'cx, 'a> {
     pub(super) fn new(cx: &'cx ExtCtxt<'a>, span: Span) -> Self {
-        Self { cx, span }
+        Self {
+            capture_decls: <_>::default(),
+            cx,
+            fmt_string: <_>::default(),
+            local_bind_decls: <_>::default(),
+            paths: <_>::default(),
+            span,
+        }
     }
 
-    /// Builds the whole `assert!` expression.
+    /// Builds the whole `assert!` expression. For example, `let elem = 1; assert!(elem == 1);` expands to:
     ///
+    /// ```rust
+    /// let elem = 1;
     /// {
-    ///    use ::core::asserting::{ ... };
+    ///   #[allow(unused_imports)]
+    ///   use ::core::asserting::{TryCaptureGeneric, TryCapturePrintable};
+    ///   let mut __capture0 = ::core::asserting::Capture::new();
+    ///   let __local_bind0 = &elem;
+    ///   if !(
+    ///     *{
+    ///       (&::core::asserting::Wrapper(__local_bind0)).try_capture(&mut __capture0);
+    ///       __local_bind0
+    ///     } == 1
+    ///   ) {
+    ///     panic!("Assertion failed: elem == 1\nWith captures:\n  elem = {}", __capture0)
+    ///   }
+    /// }
+    /// ```
+    pub(super) fn build(mut self, mut cond_expr: P<Expr>, panic_path: Path) -> P<Expr> {
+        let expr_str = pprust::expr_to_string(&cond_expr);
+        self.manage_cond_expr(&mut cond_expr);
+        let initial_imports = self.build_initial_imports();
+        let panic = self.build_panic(&expr_str, panic_path);
+
+        let Self { capture_decls, cx, local_bind_decls, span, .. } = self;
+
+        let mut stmts = Vec::with_capacity(4);
+        stmts.push(initial_imports);
+        stmts.extend(capture_decls.into_iter().map(|c| c.decl));
+        stmts.extend(local_bind_decls);
+        stmts.push(cx.stmt_expr(expr_if_not(cx, span, cond_expr, panic, None)));
+        cx.expr_block(cx.block(span, stmts))
+    }
+
+    /// Initial **trait** imports
+    ///
+    /// use ::core::asserting::{ ... };
+    fn build_initial_imports(&self) -> Stmt {
+        let nested_tree = |this: &Self, sym| {
+            (
+                UseTree {
+                    prefix: this.cx.path(this.span, vec![Ident::with_dummy_span(sym)]),
+                    kind: UseTreeKind::Simple(None, DUMMY_NODE_ID, DUMMY_NODE_ID),
+                    span: this.span,
+                },
+                DUMMY_NODE_ID,
+            )
+        };
+        self.cx.stmt_item(
+            self.span,
+            self.cx.item(
+                self.span,
+                Ident::empty(),
+                vec![self.cx.attribute(attr::mk_list_item(
+                    Ident::new(sym::allow, self.span),
+                    vec![attr::mk_nested_word_item(Ident::new(sym::unused_imports, self.span))],
+                ))],
+                ItemKind::Use(UseTree {
+                    prefix: self.cx.path(self.span, self.cx.std_path(&[sym::asserting])),
+                    kind: UseTreeKind::Nested(vec![
+                        nested_tree(self, sym::TryCaptureGeneric),
+                        nested_tree(self, sym::TryCapturePrintable),
+                    ]),
+                    span: self.span,
+                }),
+            ),
+        )
+    }
+
+    /// The necessary custom `panic!(...)` expression.
+    ///
+    /// panic!(
+    ///     "Assertion failed: ... \n With expansion: ...",
+    ///     __capture0,
+    ///     ...
+    /// );
+    fn build_panic(&self, expr_str: &str, panic_path: Path) -> P<Expr> {
+        let escaped_expr_str = escape_to_fmt(expr_str);
+        let initial = [
+            TokenTree::token(
+                token::Literal(token::Lit {
+                    kind: token::LitKind::Str,
+                    symbol: Symbol::intern(&if self.fmt_string.is_empty() {
+                        format!("Assertion failed: {escaped_expr_str}")
+                    } else {
+                        format!(
+                            "Assertion failed: {escaped_expr_str}\nWith captures:\n{}",
+                            &self.fmt_string
+                        )
+                    }),
+                    suffix: None,
+                }),
+                self.span,
+            ),
+            TokenTree::token(token::Comma, self.span),
+        ];
+        let captures = self.capture_decls.iter().flat_map(|cap| {
+            [
+                TokenTree::token(token::Ident(cap.ident.name, false), cap.ident.span),
+                TokenTree::token(token::Comma, self.span),
+            ]
+        });
+        self.cx.expr(
+            self.span,
+            ExprKind::MacCall(MacCall {
+                path: panic_path,
+                args: P(MacArgs::Delimited(
+                    DelimSpan::from_single(self.span),
+                    MacDelimiter::Parenthesis,
+                    initial.into_iter().chain(captures).collect::<TokenStream>(),
+                )),
+                prior_type_ascription: None,
+            }),
+        )
+    }
+
+    /// Recursive function called until `cond_expr` and `fmt_str` are fully modified.
+    ///
+    /// See [Self::manage_initial_capture] and [Self::manage_try_capture]
+    fn manage_cond_expr(&mut self, expr: &mut P<Expr>) {
+        match (*expr).kind {
+            ExprKind::Binary(_, ref mut lhs, ref mut rhs) => {
+                self.manage_cond_expr(lhs);
+                self.manage_cond_expr(rhs);
+            }
+            ExprKind::Path(_, Path { ref segments, .. }) if let &[ref path_segment] = &segments[..] => {
+                let path_ident = path_segment.ident;
+                self.manage_initial_capture(expr, path_ident);
+            }
+            _ => {}
+        }
+    }
+
+    /// Pushes the top-level declarations and modifies `expr` to try capturing variables.
     ///
-    ///    let mut __capture0 = Capture::new();
-    ///    ...
-    ///    ...
-    ///    ...
+    /// `fmt_str`, the formatting string used for debugging, is constructed to show possible
+    /// captured variables.
+    fn manage_initial_capture(&mut self, expr: &mut P<Expr>, path_ident: Ident) {
+        if self.paths.contains(&path_ident) {
+            return;
+        } else {
+            self.fmt_string.push_str("  ");
+            self.fmt_string.push_str(path_ident.as_str());
+            self.fmt_string.push_str(" = {:?}\n");
+            let _ = self.paths.insert(path_ident);
+        }
+        let curr_capture_idx = self.capture_decls.len();
+        let capture_string = format!("__capture{curr_capture_idx}");
+        let ident = Ident::new(Symbol::intern(&capture_string), self.span);
+        let init_std_path = self.cx.std_path(&[sym::asserting, sym::Capture, sym::new]);
+        let init = self.cx.expr_call(
+            self.span,
+            self.cx.expr_path(self.cx.path(self.span, init_std_path)),
+            vec![],
+        );
+        let capture = Capture { decl: self.cx.stmt_let(self.span, true, ident, init), ident };
+        self.capture_decls.push(capture);
+        self.manage_try_capture(ident, curr_capture_idx, expr);
+    }
+
+    /// Tries to copy `__local_bindN` into `__captureN`.
     ///
-    ///    if !{
-    ///       ...
-    ///       ...
-    ///       ...
-    ///    } {
-    ///        panic!(
-    ///            "Assertion failed: ... \n With expansion: ...",
-    ///            __capture0,
-    ///            ...
-    ///            ...
-    ///            ...
-    ///        );
-    ///    }
+    /// *{
+    ///    (&Wrapper(__local_bindN)).try_capture(&mut __captureN);
+    ///    __local_bindN
     /// }
-    pub(super) fn build(self, _cond_expr: P<Expr>, _panic_path: Path) -> P<Expr> {
-        let Self { cx, span, .. } = self;
-        let stmts = Vec::new();
-        cx.expr_block(cx.block(span, stmts))
+    fn manage_try_capture(&mut self, capture: Ident, curr_capture_idx: usize, expr: &mut P<Expr>) {
+        let local_bind_string = format!("__local_bind{curr_capture_idx}");
+        let local_bind = Ident::new(Symbol::intern(&local_bind_string), self.span);
+        self.local_bind_decls.push(self.cx.stmt_let(
+            self.span,
+            false,
+            local_bind,
+            self.cx.expr_addr_of(self.span, expr.clone()),
+        ));
+        let wrapper = self.cx.expr_call(
+            self.span,
+            self.cx.expr_path(
+                self.cx.path(self.span, self.cx.std_path(&[sym::asserting, sym::Wrapper])),
+            ),
+            vec![self.cx.expr_path(Path::from_ident(local_bind))],
+        );
+        let try_capture_call = self
+            .cx
+            .stmt_expr(expr_method_call(
+                self.cx,
+                PathSegment {
+                    args: None,
+                    id: DUMMY_NODE_ID,
+                    ident: Ident::new(sym::try_capture, self.span),
+                },
+                vec![
+                    expr_paren(self.cx, self.span, self.cx.expr_addr_of(self.span, wrapper)),
+                    expr_addr_of_mut(
+                        self.cx,
+                        self.span,
+                        self.cx.expr_path(Path::from_ident(capture)),
+                    ),
+                ],
+                self.span,
+            ))
+            .add_trailing_semicolon();
+        let local_bind_path = self.cx.expr_path(Path::from_ident(local_bind));
+        let ret = self.cx.stmt_expr(local_bind_path);
+        let block = self.cx.expr_block(self.cx.block(self.span, vec![try_capture_call, ret]));
+        *expr = self.cx.expr_deref(self.span, block);
+    }
+}
+
+/// Information about a captured element.
+#[derive(Debug)]
+struct Capture {
+    // Generated indexed `Capture` statement.
+    //
+    // `let __capture{} = Capture::new();`
+    decl: Stmt,
+    // The name of the generated indexed `Capture` variable.
+    //
+    // `__capture{}`
+    ident: Ident,
+}
+
+/// Escapes to use as a formatting string.
+fn escape_to_fmt(s: &str) -> String {
+    let mut rslt = String::with_capacity(s.len());
+    for c in s.chars() {
+        rslt.extend(c.escape_debug());
+        match c {
+            '{' | '}' => rslt.push(c),
+            _ => {}
+        }
     }
+    rslt
+}
+
+fn expr_addr_of_mut(cx: &ExtCtxt<'_>, sp: Span, e: P<Expr>) -> P<Expr> {
+    cx.expr(sp, ExprKind::AddrOf(BorrowKind::Ref, Mutability::Mut, e))
+}
+
+fn expr_method_call(
+    cx: &ExtCtxt<'_>,
+    path: PathSegment,
+    args: Vec<P<Expr>>,
+    span: Span,
+) -> P<Expr> {
+    cx.expr(span, ExprKind::MethodCall(path, args, span))
+}
+
+fn expr_paren(cx: &ExtCtxt<'_>, sp: Span, e: P<Expr>) -> P<Expr> {
+    cx.expr(sp, ExprKind::Paren(e))
 }

compiler/rustc_builtin_macros/src/lib.rs

@@ -6,6 +6,7 @@
 #![feature(array_windows)]
 #![feature(box_patterns)]
 #![feature(decl_macro)]
+#![feature(if_let_guard)]
 #![feature(is_sorted)]
 #![feature(let_chains)]
 #![feature(let_else)]

compiler/rustc_span/src/symbol.rs

@@ -157,6 +157,7 @@ symbols! {
         C,
         CStr,
         CString,
+        Capture,
         Center,
         Clone,
         Continue,
@@ -267,6 +268,8 @@ symbols! {
         ToOwned,
         ToString,
         Try,
+        TryCaptureGeneric,
+        TryCapturePrintable,
         TryFrom,
         TryInto,
         Ty,
@@ -276,6 +279,7 @@ symbols! {
         UnsafeArg,
         Vec,
         VecDeque,
+        Wrapper,
         Yield,
         _DECLS,
         _Self,
@@ -358,6 +362,7 @@ symbols! {
         assert_receiver_is_total_eq,
         assert_uninit_valid,
         assert_zero_valid,
+        asserting,
         associated_const_equality,
         associated_consts,
         associated_type_bounds,
@@ -1437,6 +1442,7 @@ symbols! {
         truncf32,
         truncf64,
         try_blocks,
+        try_capture,
         try_from,
         try_into,
         try_trait_v2,
@@ -1499,6 +1505,7 @@ symbols! {
         unsized_tuple_coercion,
         unstable,
         untagged_unions,
+        unused_imports,
         unused_qualifications,
         unwind,
         unwind_attributes,

src/test/ui/macros/assert-trailing-junk.rs

@@ -1,3 +1,6 @@
+// revisions: with-generic-asset without-generic-asset
+// [with-generic-asset] compile-flags: --cfg feature="generic_assert"
+
 // Ensure assert macro does not ignore trailing garbage.
 //
 // See https://github.com/rust-lang/rust/issues/60024 for details.