Provide useful backtraces

src/SimpleTraits.jl

@@ -142,11 +142,20 @@ function traitfn(tfn)
     else
         val = :(::Type{$trait})
     end
+    # Get line info for better backtraces
+    ln = findline(tfn)
+    if isa(ln, Expr)
+        pushloc = Expr(:meta, :push_loc, ln.args[2], fname, ln.args[1])
+        poploc = Expr(:meta, :pop_loc)
+    else
+        pushloc = poploc = nothing
+    end
+    retsym = gensym()
     if hasmac
-        fn = :(@dummy $fname{$(typs...)}($val, $(args...)) = $fbody)
+        fn = :(@dummy $fname{$(typs...)}($val, $(args...)) = ($pushloc; $retsym = $fbody; $poploc; $retsym))
         fn.args[1] = mac # replace @dummy
     else
-        fn = :($fname{$(typs...)}($val, $(args...)) = $fbody)
+        fn = :($fname{$(typs...)}($val, $(args...)) = ($pushloc; $retsym = $fbody; $poploc; $retsym))
     end
     quote
         $fname{$(typs...)}($(args...)) = (Base.@_inline_meta(); $fname($curmod.trait($trait), $(strip_tpara(args)...)))
@@ -208,6 +217,20 @@ Base.next(::GenerateTypeVars{:upcase}, state) = (Symbol("X$state"), state+1) # X
 Base.next(::GenerateTypeVars{:lcase}, state) = (Symbol("x$state"), state+1)  # x1,...
 Base.done(::GenerateTypeVars, state) = false
 
+####
+# Annotating the source location
+####
+
+function findline(ex::Expr)
+    ex.head == :line && return ex
+    for a in ex.args
+        ret = findline(a)
+        isa(ret, Expr) && return ret
+    end
+    nothing
+end
+findline(arg) = nothing
+
 ####
 # Extras
 ####

test/backtraces.jl

@@ -0,0 +1,30 @@
+###### BEGIN: LINE NUMBER SENSITIVITY ##########
+@traitdef BacktraceTr{X}
+
+@traitimpl BacktraceTr{Integer}
+
+@traitfn foo{X;  BacktraceTr{X}}(A::X) = backtrace()
+@traitfn foo{X; !BacktraceTr{X}}(A::X) = backtrace()
+###### END:   LINE NUMBER SENSITIVITY ##########
+# (the tests below depend on the particular line numbers in the code above)
+
+function hasline(bt, n)
+    for b in bt
+        lkup = StackTraces.lookup(b)
+        if length(lkup) >= 2
+            l1, l2 = lkup[1], lkup[2]
+            if (contains(string(l1.file), "backtraces.jl") &&
+                l1.func == :foo &&
+                l1.line == n &&
+                contains(string(l2.file), "SimpleTraits.jl"))
+                return true
+            end
+        end
+    end
+    false
+end
+
+@test hasline(foo(1), 6)
+@test hasline(foo(1.0), 7)
+
+nothing

test/runtests.jl

@@ -101,3 +101,7 @@ trait = SimpleTraits.trait
 # Other tests
 #####
 include("base-traits.jl")
+
+if VERSION >= v"0.5.0-dev"
+    include("backtraces.jl")
+end