Add inner err capture to MacroExpansionError

Information about this inner exception is currently completely lost, so
without capturing it, there is no way for outside catchers to access
this information.

Co-authored-by: Claire Foster <[email protected]>

Author: aviatesk

src/macro_expansion.jl

@@ -78,12 +78,19 @@ struct MacroExpansionError <: Exception
     context::Union{Nothing,MacroContext}
     ex::SyntaxTree
     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)"
+    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
+    ) = new(context, ex, msg, position, err)
 end
 
-"""
-`position` - the source position relative to the node - may be `:begin` or `:end` or `:all`
-"""
 function MacroExpansionError(ex::SyntaxTree, msg::AbstractString; position=:all)
     MacroExpansionError(nothing, ex, msg, position)
 end
@@ -126,8 +133,8 @@ function eval_macro_name(ctx::MacroExpansionContext, mctx::MacroContext, ex::Syn
     expr_form = to_lowered_expr(mod, ex5)
     try
         eval(mod, expr_form)
-    catch
-        throw(MacroExpansionError(mctx, ex, "Macro not found", :all))
+    catch err
+        throw(MacroExpansionError(mctx, ex, "Macro not found", :all, err))
     end
 end
 
@@ -152,14 +159,16 @@ function expand_macro(ctx::MacroExpansionContext, ex::SyntaxTree)
         # TODO: Allow invoking old-style macros for compat
         invokelatest(macfunc, macro_args...)
     catch exc
-        # TODO: Using rethrow() is kinda ugh. Is there a way to avoid it?
-        # NOTE: Although currently rethrow() is necessary to allow outside catchers to access full stacktrace information
         if exc isa MacroExpansionError
             # Add context to the error.
-            rethrow(MacroExpansionError(mctx, exc.ex, exc.msg, exc.position))
+            newexc = isdefined(exc, :err) ?
+                MacroExpansionError(mctx, exc.ex, exc.msg, exc.position, exc.err) :
+                MacroExpansionError(mctx, exc.ex, exc.msg, exc.position)
         else
-            rethrow(MacroExpansionError(mctx, ex, "Error expanding macro", :all))
+            newexc = MacroExpansionError(mctx, ex, "Error expanding macro", :all, exc)
         end
+        # TODO: We can delete this rethrow when we move to AST-based error propagation.
+        rethrow(newexc)
     end
 
     if expanded isa SyntaxTree

test/macros.jl

@@ -156,6 +156,7 @@ let (err, st) = try
         e, stacktrace(catch_backtrace())
     end
     @test err isa JuliaLowering.MacroExpansionError
+    @test isdefined(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)
@@ -168,6 +169,7 @@ let res = try
     end
     @test res isa JuliaLowering.MacroExpansionError
     @test res.msg == "Macro not found"
+    @test isdefined(res, :err) && res.err isa UndefVarError
 end
 
 include("ccall_demo.jl")
@@ -179,6 +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)
     # Check that `catch_backtrace` can capture the stacktrace of the macro function
     @test any(sf->sf.func===:ccall_macro_parse, st)
 end