always set err field of MacroExpansionError

Author: aviatesk

src/macro_expansion.jl

@@ -80,14 +80,11 @@ struct MacroExpansionError <: Exception
     msg::String
     "The source position relative to the node - may be `:begin` or `:end` or `:all`"
     position::Symbol
-    "Error that occurred inside the macro function call (note that this may not be defined)"
+    "Error that occurred inside the macro function call (`nothing` if no inner exception)"
     err
-    MacroExpansionError(
-        context::Union{Nothing,MacroContext}, ex::SyntaxTree, msg::AbstractString, position::Symbol
-    ) = new(context, ex, msg, position)
     MacroExpansionError(
         context::Union{Nothing,MacroContext}, ex::SyntaxTree, msg::AbstractString, position::Symbol,
-        @nospecialize err
+        @nospecialize err = nothing
     ) = new(context, ex, msg, position, err)
 end
 
@@ -161,9 +158,7 @@ function expand_macro(ctx::MacroExpansionContext, ex::SyntaxTree)
     catch exc
         if exc isa MacroExpansionError
             # Add context to the error.
-            newexc = isdefined(exc, :err) ?
-                MacroExpansionError(mctx, exc.ex, exc.msg, exc.position, exc.err) :
-                MacroExpansionError(mctx, exc.ex, exc.msg, exc.position)
+            newexc = MacroExpansionError(mctx, exc.ex, exc.msg, exc.position, exc.err)
         else
             newexc = MacroExpansionError(mctx, ex, "Error expanding macro", :all, exc)
         end

test/macros.jl

@@ -156,20 +156,20 @@ let (err, st) = try
         e, stacktrace(catch_backtrace())
     end
     @test err isa JuliaLowering.MacroExpansionError
-    @test isdefined(err, :err)
+    @test !isnothing(err.err)
     # Check that `catch_backtrace` can capture the stacktrace of the macro functions
     @test any(sf->sf.func===:f_throw, st)
     @test any(sf->sf.func===Symbol("@m_throw"), st)
 end
 
-let res = try
+let err = try
         JuliaLowering.include_string(test_mod, "_never_exist = @m_not_exist 42")
     catch e
         e
     end
-    @test res isa JuliaLowering.MacroExpansionError
-    @test res.msg == "Macro not found"
-    @test isdefined(res, :err) && res.err isa UndefVarError
+    @test err isa JuliaLowering.MacroExpansionError
+    @test err.msg == "Macro not found"
+    @test err.err isa UndefVarError
 end
 
 include("ccall_demo.jl")
@@ -181,7 +181,7 @@ let (err, st) = try
     end
     @test err isa JuliaLowering.MacroExpansionError
     @test err.msg == "Expected a return type annotation like `::T`"
-    @test !isdefined(err, :err)
+    @test isnothing(err.err)
     # Check that `catch_backtrace` can capture the stacktrace of the macro function
     @test any(sf->sf.func===:ccall_macro_parse, st)
 end