Provide Position to debug.

RELEASES.md

@@ -14,11 +14,13 @@ Breaking changes
 ----------------
 
 * `Engine::on_progress` now takes `u64` instead of `&u64`.
+* The closure for `Engine::on_debug` now takes an additional `Position` parameter.
 
 Enhancements
 ------------
 
 * Capturing a constant variable in a closure is now supported, with no cloning.
+* Provides position info for `debug` statements.
 
 
 Version 0.19.7

doc/src/language/print-debug.md

@@ -22,10 +22,12 @@ When embedding Rhai into an application, it is usually necessary to trap `print`
 (for logging into a tracking log, for example) with the `Engine::on_print` and `Engine::on_debug` methods:
 
 ```rust
-// Any function or closure that takes an '&str' argument can be used to override
-// 'print' and 'debug'
+// Any function or closure that takes an '&str' argument can be used to override 'print'.
 engine.on_print(|x| println!("hello: {}", x));
-engine.on_debug(|x| println!("DEBUG: {}", x));
+
+// Any function or closure that takes a '&str' and a 'Position' argument can be used to
+// override 'debug'.
+engine.on_debug(|x, pos| println!("DEBUG at {:?}: {}", pos, x));
 
 // Example: quick-'n-dirty logging
 let logbook = Arc::new(RwLock::new(Vec::<String>::new()));
@@ -35,7 +37,9 @@ let log = logbook.clone();
 engine.on_print(move |s| log.write().unwrap().push(format!("entry: {}", s)));
 
 let log = logbook.clone();
-engine.on_debug(move |s| log.write().unwrap().push(format!("DEBUG: {}", s)));
+engine.on_debug(move |s, pos| log.write().unwrap().push(
+                                    format!("DEBUG at {:?}: {}", pos, s)
+                              ));
 
 // Evaluate script
 engine.eval::<()>(script)?;

src/engine.rs

@@ -4,7 +4,8 @@ use crate::ast::{Expr, FnCallExpr, Ident, IdentX, ReturnType, Stmt};
 use crate::dynamic::{map_std_type_name, AccessMode, Union, Variant};
 use crate::fn_call::run_builtin_op_assignment;
 use crate::fn_native::{
-    CallableFunction, IteratorFn, OnPrintCallback, OnProgressCallback, OnVarCallback,
+    CallableFunction, IteratorFn, OnDebugCallback, OnPrintCallback, OnProgressCallback,
+    OnVarCallback,
 };
 use crate::module::NamespaceRef;
 use crate::optimize::OptimizationLevel;
@@ -626,7 +627,7 @@ pub struct Engine {
     /// Callback closure for implementing the `print` command.
     pub(crate) print: OnPrintCallback,
     /// Callback closure for implementing the `debug` command.
-    pub(crate) debug: OnPrintCallback,
+    pub(crate) debug: OnDebugCallback,
     /// Callback closure for progress reporting.
     pub(crate) progress: Option<OnProgressCallback>,
 
@@ -677,7 +678,7 @@ pub fn is_anonymous_fn(fn_name: &str) -> bool {
     fn_name.starts_with(FN_ANONYMOUS)
 }
 
-/// Print/debug to stdout
+/// Print to stdout
 #[inline(always)]
 fn default_print(_s: &str) {
     #[cfg(not(feature = "no_std"))]
@@ -685,6 +686,14 @@ fn default_print(_s: &str) {
     println!("{}", _s);
 }
 
+/// Debug to stdout
+#[inline(always)]
+fn default_debug(_s: &str, _pos: Position) {
+    #[cfg(not(feature = "no_std"))]
+    #[cfg(not(target_arch = "wasm32"))]
+    println!("{:?} | {}", _pos, _s);
+}
+
 /// Search for a module within an imports stack.
 /// [`Position`] in [`EvalAltResult`] is [`None`][Position::None] and must be set afterwards.
 pub fn search_imports(
@@ -741,7 +750,7 @@ impl Engine {
 
             // default print/debug implementations
             print: Box::new(default_print),
-            debug: Box::new(default_print),
+            debug: Box::new(default_debug),
 
             // progress callback
             progress: None,
@@ -797,7 +806,7 @@ impl Engine {
             resolve_var: None,
 
             print: Box::new(|_| {}),
-            debug: Box::new(|_| {}),
+            debug: Box::new(|_, _| {}),
             progress: None,
 
             optimization_level: if cfg!(feature = "no_optimize") {

src/engine_api.rs

@@ -1808,16 +1808,21 @@ impl Engine {
     ///
     /// // Override action of 'print' function
     /// let logger = result.clone();
-    /// engine.on_debug(move |s| logger.write().unwrap().push_str(s));
+    /// engine.on_debug(move |s, pos| logger.write().unwrap().push_str(
+    ///                                 &format!("{:?} > {}", pos, s)
+    ///                               ));
     ///
-    /// engine.consume(r#"debug("hello");"#)?;
+    /// engine.consume(r#"let x = "hello"; debug(x);"#)?;
     ///
-    /// assert_eq!(*result.read().unwrap(), r#""hello""#);
+    /// assert_eq!(*result.read().unwrap(), r#"1:18 > "hello""#);
     /// # Ok(())
     /// # }
     /// ```
     #[inline(always)]
-    pub fn on_debug(&mut self, callback: impl Fn(&str) + SendSync + 'static) -> &mut Self {
+    pub fn on_debug(
+        &mut self,
+        callback: impl Fn(&str, Position) + SendSync + 'static,
+    ) -> &mut Self {
         self.debug = Box::new(callback);
         self
     }

src/fn_call.rs

@@ -211,13 +211,16 @@ impl Engine {
                     false,
                 ),
                 KEYWORD_DEBUG => (
-                    (self.debug)(result.as_str().map_err(|typ| {
+                    (self.debug)(
+                        result.as_str().map_err(|typ| {
                             EvalAltResult::ErrorMismatchOutputType(
                                 self.map_type_name(type_name::<ImmutableString>()).into(),
                                 typ.into(),
                                 pos,
                             )
-                    })?)
+                        })?,
+                        pos,
+                    )
                     .into(),
                     false,
                 ),

src/fn_native.rs

@@ -356,7 +356,14 @@ pub type OnProgressCallback = Box<dyn Fn(u64) -> Option<Dynamic> + Send + Sync +
 pub type OnPrintCallback = Box<dyn Fn(&str) + 'static>;
 /// A standard callback function for printing.
 #[cfg(feature = "sync")]
-pub type OnPrintCallback<T, R> = Box<dyn Fn(&str) + Send + Sync + 'static>;
+pub type OnPrintCallback = Box<dyn Fn(&str) + Send + Sync + 'static>;
+
+/// A standard callback function for debugging.
+#[cfg(not(feature = "sync"))]
+pub type OnDebugCallback = Box<dyn Fn(&str, Position) + 'static>;
+/// A standard callback function for debugging.
+#[cfg(feature = "sync")]
+pub type OnDebugCallback = Box<dyn Fn(&str, Position) + Send + Sync + 'static>;
 
 /// A standard callback function for variable access.
 #[cfg(not(feature = "sync"))]

tests/print.rs

@@ -2,7 +2,7 @@ use rhai::{Engine, EvalAltResult, RegisterFn, INT};
 use std::sync::{Arc, RwLock};
 
 #[test]
-fn test_print() -> Result<(), Box<EvalAltResult>> {
+fn test_print_debug() -> Result<(), Box<EvalAltResult>> {
     let logbook = Arc::new(RwLock::new(Vec::<String>::new()));
 
     // Redirect print/debug output to 'log'
@@ -13,16 +13,20 @@ fn test_print() -> Result<(), Box<EvalAltResult>> {
 
     engine
         .on_print(move |s| log1.write().unwrap().push(format!("entry: {}", s)))
-        .on_debug(move |s| log2.write().unwrap().push(format!("DEBUG: {}", s)));
+        .on_debug(move |s, pos| {
+            log2.write()
+                .unwrap()
+                .push(format!("DEBUG at {:?}: {}", pos, s))
+        });
 
     // Evaluate script
     engine.eval::<()>("print(40 + 2)")?;
-    engine.eval::<()>(r#"debug("hello!")"#)?;
+    engine.eval::<()>(r#"let x = "hello!"; debug(x)"#)?;
 
     // 'logbook' captures all the 'print' and 'debug' output
     assert_eq!(logbook.read().unwrap().len(), 2);
     assert_eq!(logbook.read().unwrap()[0], "entry: 42");
-    assert_eq!(logbook.read().unwrap()[1], r#"DEBUG: "hello!""#);
+    assert_eq!(logbook.read().unwrap()[1], r#"DEBUG at 1:19: "hello!""#);
 
     for entry in logbook.read().unwrap().iter() {
         println!("{}", entry);