Make tracing an opt-in feature (#2709)

This PR adds the `"trace"` feature flag that enables vm opcode tracing (off by default), most users aren't interested in tracing/debugging that's why I think it should be made out-in.

boa_cli/Cargo.toml

@@ -12,7 +12,7 @@ repository.workspace = true
 rust-version.workspace = true
 
 [dependencies]
-boa_engine = { workspace = true, features = ["deser", "console", "flowgraph"] }
+boa_engine = { workspace = true, features = ["deser", "console", "flowgraph", "trace"] }
 boa_ast = { workspace = true, features = ["serde"]}
 boa_parser.workspace = true
 rustyline = { version = "11.0.0", features = ["derive"]}

boa_engine/Cargo.toml

@@ -33,6 +33,9 @@ fuzz = ["boa_ast/arbitrary", "boa_interner/arbitrary"]
 # Enable Boa's VM instruction flowgraph generator.
 flowgraph = []
 
+# Enable Boa's VM instruction tracing.
+trace = []
+
 # Enable Boa's WHATWG console object implementation.
 console = []
 

boa_engine/src/context/mod.rs

@@ -422,6 +422,7 @@ impl Context<'_> {
     }
 
     /// Set the value of trace on the context
+    #[cfg(feature = "trace")]
     pub fn set_trace(&mut self, trace: bool) {
         self.vm.trace = trace;
     }

boa_engine/src/vm/code_block.rs

@@ -18,7 +18,7 @@ use crate::{
     },
     property::PropertyDescriptor,
     string::utf16,
-    vm::{CallFrame, Opcode},
+    vm::CallFrame,
     Context, JsResult, JsString, JsValue,
 };
 use boa_ast::{
@@ -26,9 +26,14 @@ use boa_ast::{
     function::{FormalParameterList, PrivateName},
 };
 use boa_gc::{Finalize, Gc, GcRefCell, Trace};
-use boa_interner::{Interner, Sym, ToInternedString};
+use boa_interner::Sym;
 use boa_profiler::Profiler;
-use std::{collections::VecDeque, convert::TryInto, mem::size_of};
+use std::{collections::VecDeque, mem::size_of};
+
+#[cfg(any(feature = "trace", feature = "flowgraph"))]
+use crate::vm::Opcode;
+#[cfg(any(feature = "trace", feature = "flowgraph"))]
+use boa_interner::{Interner, ToInternedString};
 
 /// This represents whether a value can be read from [`CodeBlock`] code.
 ///
@@ -190,6 +195,7 @@ impl CodeBlock {
     /// Modifies the `pc` to point to the next instruction.
     ///
     /// Returns an empty `String` if no operands are present.
+    #[cfg(any(feature = "trace", feature = "flowgraph"))]
     pub(crate) fn instruction_operands(&self, pc: &mut usize, interner: &Interner) -> String {
         let opcode: Opcode = self.bytecode[*pc].try_into().expect("invalid opcode");
         *pc += size_of::<Opcode>();
@@ -450,6 +456,7 @@ impl CodeBlock {
     }
 }
 
+#[cfg(any(feature = "trace", feature = "flowgraph"))]
 impl ToInternedString for CodeBlock {
     fn to_interned_string(&self, interner: &Interner) -> String {
         let name = interner.resolve_expect(self.name);

boa_engine/src/vm/mod.rs

@@ -11,9 +11,13 @@ use crate::{
 };
 #[cfg(feature = "fuzz")]
 use crate::{JsNativeError, JsNativeErrorKind};
-use boa_interner::ToInternedString;
 use boa_profiler::Profiler;
-use std::{convert::TryInto, mem::size_of, time::Instant};
+use std::{convert::TryInto, mem::size_of};
+
+#[cfg(feature = "trace")]
+use boa_interner::ToInternedString;
+#[cfg(feature = "trace")]
+use std::time::Instant;
 
 mod call_frame;
 mod code_block;
@@ -40,6 +44,7 @@ pub struct Vm {
     pub(crate) frames: Vec<CallFrame>,
     pub(crate) stack: Vec<JsValue>,
     pub(crate) err: Option<JsError>,
+    #[cfg(feature = "trace")]
     pub(crate) trace: bool,
     pub(crate) stack_size_limit: usize,
 }
@@ -50,6 +55,7 @@ impl Default for Vm {
             frames: Vec::with_capacity(16),
             stack: Vec::with_capacity(1024),
             err: None,
+            #[cfg(feature = "trace")]
             trace: false,
             stack_size_limit: 1024,
         }
@@ -133,14 +139,20 @@ impl Context<'_> {
     }
 
     pub(crate) fn run(&mut self) -> CompletionRecord {
+        #[cfg(feature = "trace")]
         const COLUMN_WIDTH: usize = 26;
+        #[cfg(feature = "trace")]
         const TIME_COLUMN_WIDTH: usize = COLUMN_WIDTH / 2;
+        #[cfg(feature = "trace")]
         const OPCODE_COLUMN_WIDTH: usize = COLUMN_WIDTH;
+        #[cfg(feature = "trace")]
         const OPERAND_COLUMN_WIDTH: usize = COLUMN_WIDTH;
+        #[cfg(feature = "trace")]
         const NUMBER_OF_COLUMNS: usize = 4;
 
         let _timer = Profiler::global().start_event("run", "vm");
 
+        #[cfg(feature = "trace")]
         if self.vm.trace {
             let msg = if self.vm.frames.last().is_some() {
                 " Call Frame "
@@ -203,6 +215,7 @@ impl Context<'_> {
             }
 
             // 1. Run the next instruction.
+            #[cfg(feature = "trace")]
             let result = if self.vm.trace {
                 let mut pc = self.vm.frame().pc;
                 let opcode: Opcode = self
@@ -239,6 +252,9 @@ impl Context<'_> {
                 self.execute_instruction()
             };
 
+            #[cfg(not(feature = "trace"))]
+            let result = self.execute_instruction();
+
             // 2. Evaluate the result of executing the instruction.
             match result {
                 Ok(CompletionType::Normal) => {}
@@ -295,6 +311,7 @@ impl Context<'_> {
             }
         }
 
+        #[cfg(feature = "trace")]
         if self.vm.trace {
             println!("\nStack:");
             if self.vm.stack.is_empty() {