Make assert macro a built-in procedural macro

src/libsyntax_ext/assert.rs

@@ -0,0 +1,64 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use syntax::ast::*;
+use syntax::codemap::Spanned;
+use syntax::ext::base::*;
+use syntax::ext::build::AstBuilder;
+use syntax::parse::token;
+use syntax::print::pprust;
+use syntax::tokenstream::{TokenStream, TokenTree};
+use syntax_pos::Span;
+
+pub fn expand_assert<'cx>(
+    cx: &'cx mut ExtCtxt,
+    sp: Span,
+    tts: &[TokenTree],
+) -> Box<MacResult + 'cx> {
+    let mut parser = cx.new_parser_from_tts(tts);
+    let cond_expr = panictry!(parser.parse_expr());
+    let custom_msg_args = if parser.eat(&token::Comma) {
+        let ts = parser.parse_tokens();
+        if !ts.is_empty() {
+            Some(ts)
+        } else {
+            None
+        }
+    } else {
+        None
+    };
+
+    let sp = sp.with_ctxt(sp.ctxt().apply_mark(cx.current_expansion.mark));
+    let panic_call = Mac_ {
+        path: Path::from_ident(sp, Ident::from_str("panic")),
+        tts: if let Some(ts) = custom_msg_args {
+            ts.into()
+        } else {
+            let panic_str = format!("assertion failed: {}", pprust::expr_to_string(&cond_expr));
+            TokenStream::from(token::Literal(
+                token::Lit::Str_(Name::intern(&panic_str)),
+                None,
+            )).into()
+        },
+    };
+    let if_expr = cx.expr_if(
+        sp,
+        cx.expr(sp, ExprKind::Unary(UnOp::Not, cond_expr)),
+        cx.expr(
+            sp,
+            ExprKind::Mac(Spanned {
+                span: sp,
+                node: panic_call,
+            }),
+        ),
+        None,
+    );
+    MacEager::expr(if_expr)
+}