Support break-on-error

Author: timholy

src/JuliaInterpreter.jl

@@ -41,8 +41,10 @@ isless(x::JuliaProgramCounter, y::Integer) = isless(x.next_stmt, y)
 
 Base.show(io::IO, pc::JuliaProgramCounter) = print(io, "JuliaProgramCounter(", pc.next_stmt, ')')
 
+# Breakpoint support
 truecondition(frame) = true
 falsecondition(frame) = false
+const break_on_error = Ref(false)
 
 """
     BreakpointState(isactive=true, condition=JuliaInterpreter.truecondition)

src/breakpoints.jl

@@ -14,13 +14,17 @@ struct Unassigned end
 
 """
     BreakpointRef(framecode, stmtidx)
+    BreakpointRef(framecode, stmtidx, err)
 
 A reference to a breakpoint at a particular statement index `stmtidx` in `framecode`.
+If the break was due to an error, supply that as well.
 """
 struct BreakpointRef
     framecode::JuliaFrameCode
     stmtidx::Int
+    err
 end
+BreakpointRef(framecode, stmtidx) = BreakpointRef(framecode, stmtidx, nothing)
 
 function Base.show(io::IO, bp::BreakpointRef)
     lineno = linenumber(bp.framecode, bp.stmtidx)

src/interpret.jl

@@ -211,6 +211,7 @@ function evaluate_call!(stack, frame::JuliaStackFrame, call_expr::Expr, pc; exec
         return BreakpointRef(newframe.code, newframe.pc[])
     end
     ret = exec!(stack, newframe)
+    isa(ret, BreakpointRef) && return ret
     pop!(stack)
     push!(junk, newframe)  # rather than going through GC, just re-use it
     return ret
@@ -454,7 +455,7 @@ function _step_expr!(stack, frame, @nospecialize(node), pc::JuliaProgramCounter,
             rhs = @lookup(frame, node)
         end
     catch err
-        return handle_err(frame, err)
+        return handle_err(stack, frame, pc, err)
     end
     @isdefined(rhs) && isa(rhs, BreakpointRef) && return rhs
     if isassign(frame, pc)
@@ -484,7 +485,12 @@ function step_expr!(stack, frame, istoplevel::Bool=false)
     frame.pc[] = pc
 end
 
-function handle_err(frame, err)
+function handle_err(stack, frame, pc, err)
+    if break_on_error[]
+        frame.pc[] = pc
+        push!(stack, frame)
+        return BreakpointRef(frame.code, pc, err)
+    end
     # Check for world age errors, which generally indicate a failure to go back to toplevel
     if isa(err, MethodError)
         is_arg_types = isa(err.args, DataType)

test/breakpoints.jl

@@ -65,4 +65,16 @@ end
     bp = JuliaInterpreter.next_line!(stack, frame)
     @test isa(bp, Breakpoints.BreakpointRef)
     @test JuliaInterpreter.finish_stack!(stack) == 2
+
+    # break on error
+    inner(x) = error("oops")
+    outer() = inner(1)
+    JuliaInterpreter.break_on_error[] = true
+    stack = JuliaStackFrame[]
+    frame = JuliaInterpreter.enter_call(outer)
+    bp = JuliaInterpreter.finish_and_return!(stack, frame)
+    @test bp.err == ErrorException("oops")
+    @test length(stack) >= 2
+    @test stack[1].code.scope.name == :outer
+    @test stack[2].code.scope.name == :inner
 end