Introduce drop-bomb

3 files changed, 43 insertions, 20 deletions

diff --git a/src/drop_bomb.rs b/src/drop_bomb.rs
new file mode 100644
index 000000000..750904a01
--- /dev/null
+++ b/src/drop_bomb.rs
@@ -0,0 +1,21 @@
+use std::borrow::Cow;
+
+pub struct DropBomb {
+    msg: Cow<'static, str>,
+    defused: bool,
+}
+
+impl DropBomb {
+    pub fn new(msg: impl Into<Cow<'static, str>>) -> DropBomb {
+        DropBomb { msg: msg.into(), defused: false }
+    }
+    pub fn defuse(&mut self) { self.defused = true }
+}
+
+impl Drop for DropBomb {
+    fn drop(&mut self) {
+        if !self.defused && !::std::thread::panicking() {
+            panic!("{}", self.msg)
+        }
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
index 1cd45690a..d9572912c 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -31,6 +31,7 @@ mod lexer;
 mod parser_api;
 mod grammar;
 mod parser_impl;
+mod drop_bomb;
 
 mod syntax_kinds;
 /// Utilities for simple uses of the parser.
diff --git a/src/parser_api.rs b/src/parser_api.rs
index d12f773b2..3cad91976 100644
--- a/src/parser_api.rs
+++ b/src/parser_api.rs
@@ -1,6 +1,7 @@
 use {
     parser_impl::ParserImpl,
     SyntaxKind::{self, ERROR},
+    drop_bomb::DropBomb,
 };
 
 #[derive(Clone, Copy)]
@@ -76,7 +77,7 @@ impl<'t> Parser<'t> {
     /// consumed between the `start` and the corresponding `Marker::complete`
     /// belong to the same node.
     pub(crate) fn start(&mut self) -> Marker {
-        Marker(self.0.start())
+        Marker::new(self.0.start())
     }
 
     /// Advances the parser by one token.
@@ -131,31 +132,31 @@ impl<'t> Parser<'t> {
 }
 
 /// See `Parser::start`.
-pub(crate) struct Marker(u32);
+pub(crate) struct Marker {
+    pos: u32,
+    bomb: DropBomb,
+}
 
 impl Marker {
+    fn new(pos: u32) -> Marker {
+        Marker {
+            pos,
+            bomb: DropBomb::new("Marker must be either completed or abandoned")
+        }
+    }
+
     /// Finishes the syntax tree node and assigns `kind` to it.
-    pub(crate) fn complete(self, p: &mut Parser, kind: SyntaxKind) -> CompletedMarker {
-        let pos = self.0;
-        ::std::mem::forget(self);
-        p.0.complete(pos, kind);
-        CompletedMarker(pos)
+    pub(crate) fn complete(mut self, p: &mut Parser, kind: SyntaxKind) -> CompletedMarker {
+        self.bomb.defuse();
+        p.0.complete(self.pos, kind);
+        CompletedMarker(self.pos)
     }
 
     /// Abandons the syntax tree node. All its children
     /// are attached to its parent instead.
-    pub(crate) fn abandon(self, p: &mut Parser) {
-        let pos = self.0;
-        ::std::mem::forget(self);
-        p.0.abandon(pos);
-    }
-}
-
-impl Drop for Marker {
-    fn drop(&mut self) {
-        if !::std::thread::panicking() {
-            panic!("Marker must be either completed or abandoned");
-        }
+    pub(crate) fn abandon(mut self, p: &mut Parser) {
+        self.bomb.defuse();
+        p.0.abandon(self.pos);
     }
 }
 
@@ -170,6 +171,6 @@ impl CompletedMarker {
     /// `B` before starting `A`. `precede` allows to do exactly
     /// that. See also docs about `forward_parent` in `Event::Start`.
     pub(crate) fn precede(self, p: &mut Parser) -> Marker {
-        Marker(p.0.precede(self.0))
+        Marker::new(p.0.precede(self.0))
     }
 }