Allow self-terminating custom syntax.

CHANGELOG.md

@@ -8,6 +8,7 @@ Enhancements
 ------------
 
 * `$symbol$` is supported in custom syntax to match any symbol.
+* Custom syntax with `$block$`, `}` or `;` as the last symbol are now self-terminating (i.e. no need to attach a terminating `;`).
 * `Dynamic::as_string` and `Dynamic::as_immutable_string` are deprecated and replaced by `into_string` and `into_immutable_string` respectively.
 * Added a number of constants to `Dynamic`.
 * Added a number of constants and `fromXXX` constant methods to `Dynamic`.

src/ast.rs

@@ -1263,10 +1263,12 @@ impl Stmt {
             // A No-op requires a semicolon in order to know it is an empty statement!
             Self::Noop(_) => false,
 
+            Self::Expr(Expr::Custom(x, _)) if x.is_self_terminated() => true,
+
             Self::Var(_, _, _, _)
             | Self::Assignment(_, _)
-            | Self::FnCall(_, _)
             | Self::Expr(_)
+            | Self::FnCall(_, _)
             | Self::Do(_, _, _, _)
             | Self::Continue(_)
             | Self::Break(_)
@@ -1509,6 +1511,19 @@ pub struct CustomExpr {
     pub scope_may_be_changed: bool,
     /// List of tokens actually parsed.
     pub tokens: StaticVec<Identifier>,
+    /// Is this custom syntax self-terminated?
+    pub self_terminated: bool,
+}
+
+impl CustomExpr {
+    /// Is this custom syntax self-terminated (i.e. no need for a semicolon terminator)?
+    ///
+    /// A self-terminated custom syntax always ends in `$block$`, `}` or `;`
+    #[must_use]
+    #[inline(always)]
+    pub const fn is_self_terminated(&self) -> bool {
+        self.self_terminated
+    }
 }
 
 /// _(internals)_ A binary expression.

src/parse.rs

@@ -2004,16 +2004,17 @@ fn parse_custom_syntax(
     }
 
     let parse_func = syntax.parse.as_ref();
+    let mut required_token: ImmutableString = key.into();
 
-    segments.push(key.into());
-    tokens.push(key.into());
+    tokens.push(required_token.clone().into());
+    segments.push(required_token.clone());
 
     loop {
         let (fwd_token, fwd_pos) = input.peek().expect(NEVER_ENDS);
         settings.pos = *fwd_pos;
         let settings = settings.level_up();
 
-        let required_token = match parse_func(&segments, fwd_token.syntax().as_ref()) {
+        required_token = match parse_func(&segments, fwd_token.syntax().as_ref()) {
             Ok(Some(seg)) => seg,
             Ok(None) => break,
             Err(err) => return Err(err.0.into_err(settings.pos)),
@@ -2120,11 +2121,23 @@ fn parse_custom_syntax(
     keywords.shrink_to_fit();
     tokens.shrink_to_fit();
 
+    const KEYWORD_SEMICOLON: &str = Token::SemiColon.literal_syntax();
+    const KEYWORD_CLOSE_BRACE: &str = Token::RightBrace.literal_syntax();
+
+    let self_terminated = match required_token.as_str() {
+        // It is self-terminating if the last symbol is a block
+        CUSTOM_SYNTAX_MARKER_BLOCK => true,
+        // If the last symbol is `;` or `}`, it is self-terminating
+        KEYWORD_SEMICOLON | KEYWORD_CLOSE_BRACE => true,
+        _ => false,
+    };
+
     Ok(Expr::Custom(
         CustomExpr {
             keywords,
             tokens,
             scope_may_be_changed: syntax.scope_may_be_changed,
+            self_terminated,
         }
         .into(),
         pos,

tests/custom_syntax.rs

@@ -136,6 +136,16 @@ fn test_custom_syntax() -> Result<(), Box<EvalAltResult>> {
         ))
     );
 
+    // Check self-termination
+    engine
+        .register_custom_syntax(&["test1", "$block$"], true, |_, _| Ok(Dynamic::UNIT))?
+        .register_custom_syntax(&["test2", "}"], true, |_, _| Ok(Dynamic::UNIT))?
+        .register_custom_syntax(&["test3", ";"], true, |_, _| Ok(Dynamic::UNIT))?;
+
+    assert_eq!(engine.eval::<INT>("test1 { x = y + z; } 42")?, 42);
+    assert_eq!(engine.eval::<INT>("test2 } 42")?, 42);
+    assert_eq!(engine.eval::<INT>("test3; 42")?, 42);
+
     Ok(())
 }