add a function to extract local variables from a frame (#54)

Author: KristofferC

docs/src/dev_reference.md

@@ -73,4 +73,6 @@ JuliaInterpreter.iswrappercall
 JuliaInterpreter.isdocexpr
 JuliaInterpreter.isglobalref
 JuliaInterpreter.statementnumber
+JuliaInterpreter.Variable
+JuliaInterpreter.locals
 ```

src/JuliaInterpreter.jl

@@ -158,6 +158,51 @@ end
 JuliaStackFrame(frame::JuliaStackFrame, pc::JuliaProgramCounter; kwargs...) =
     JuliaStackFrame(frame.code, frame, pc; kwargs...)
 
+"""
+`Variable` is a struct representing a variable with an asigned value.
+By calling the function `locals`[@ref] on a `JuliaStackFrame`[@ref] a
+`Vector` of `Variable`'s is returned.
+
+Important fields:
+- `value::Any`: the value of the local variable
+- `name::Symbol`: the name of the variable as given in the source code
+- `isparam::Bool`: if the variable is a type parameter, for example `T` in `f(x::T) where {T} = x` .
+"""
+struct Variable
+    value::Any
+    name::Symbol
+    isparam::Bool
+end
+Base.show(io::IO, var::Variable) = print(io, var.name, " = ", var.value)
+Base.isequal(var1::Variable, var2::Variable) = 
+    var1.value == var2.value && var1.name == var2.name && var1.isparam == var2.isparam
+
+"""
+    local_variables = locals(frame::JuliaStackFrame)::Vector{Variable}
+
+Return the local variables as a vector of `Variable`[@ref].
+"""
+function locals(frame::JuliaStackFrame)
+    vars = Variable[]
+    syms = Set{Symbol}()
+    for i = length(frame.locals):-1:1
+        if !isa(frame.locals[i], Nothing)
+            sym = frame.code.code.slotnames[i]
+            sym in syms && continue
+            push!(vars, Variable(something(frame.locals[i]), sym, false))
+            push!(syms, sym)
+        end
+    end
+    reverse!(vars)
+    if frame.code.scope isa Method
+        syms = sparam_syms(frame.code.scope)
+        for i in 1:length(syms)
+            push!(vars, Variable(frame.sparams[i], syms[i], true))
+        end
+    end
+    return vars
+end
+
 """
 `framedict[method]` returns the `JuliaFrameCode` for `method`. For `@generated` methods,
 see [`genframedict`](@ref).

test/interpret.jl

@@ -274,3 +274,39 @@ end
 # Some expression can appear nontrivial but lower to nothing
 @test isa(JuliaInterpreter.prepare_thunk(Main, :(@static if ccall(:jl_get_UNAME, Any, ()) == :NoOS 1+1 end)), Nothing)
 @test isa(JuliaInterpreter.prepare_thunk(Main, :(Base.BaseDocs.@kw_str "using")), Nothing)
+
+@testset "locals" begin
+    f_locals(x::Int64, y::T, z::Vararg{Symbol}) where {T} = x
+    frame = JuliaInterpreter.enter_call(f_locals, 1, 2.0, :a, :b)
+    locals = JuliaInterpreter.locals(frame)
+    @test JuliaInterpreter.Variable(1, :x, false) in locals
+    @test JuliaInterpreter.Variable(2.0, :y, false) in locals
+    @test JuliaInterpreter.Variable((:a, :b), :z, false) in locals
+    @test JuliaInterpreter.Variable(Float64, :T, true) in locals
+
+    function f_multi(x)
+        c = x
+        x = 2
+        x = 3
+        x = 4
+        return x
+    end
+    frame = JuliaInterpreter.enter_call(f_multi, 1)
+    stack = [frame]
+    locals = JuliaInterpreter.locals(frame)
+    @test length(locals) == 2
+    @test JuliaInterpreter.Variable(1, :x, false) in locals
+    JuliaInterpreter.step_expr!(stack, frame)
+    JuliaInterpreter.step_expr!(stack, frame)
+    locals = JuliaInterpreter.locals(frame)
+    @test length(locals) == 3
+    @test JuliaInterpreter.Variable(1, :c, false) in locals
+    JuliaInterpreter.step_expr!(stack, frame)
+    locals = JuliaInterpreter.locals(frame)
+    @test length(locals) == 3
+    @test JuliaInterpreter.Variable(2, :x, false) in locals
+    JuliaInterpreter.step_expr!(stack, frame)
+    locals = JuliaInterpreter.locals(frame)
+    @test length(locals) == 3
+    @test JuliaInterpreter.Variable(3, :x, false) in locals
+end