add some checks for invalid expressions (JuliaLang#35363)

add null check for module-default-defs, fix JuliaLang#34544

fix JuliaLang#35367 as well

change jl_eval_module_expr to check 3rd arg is block

Author: ssikdar1

src/ast.c

@@ -577,7 +577,7 @@ static jl_value_t *scm_to_julia_(fl_context_t *fl_ctx, value_t e, jl_module_t *m
             assert(jl_is_symbol(ex));
             temp = jl_module_globalref(jl_core_module, (jl_sym_t*)ex);
         }
-        else if (sym == inert_sym || (sym == quote_sym && (!iscons(car_(e))))) {
+        else if (iscons(e) && (sym == inert_sym || (sym == quote_sym && (!iscons(car_(e)))))) {
             ex = scm_to_julia_(fl_ctx, car_(e), mod);
             temp = jl_new_struct(jl_quotenode_type, ex);
         }

src/jlfrontend.scm

@@ -176,7 +176,7 @@
   (jl-expand-to-thunk
    (let* ((name (caddr e))
           (body (cadddr e))
-          (loc  (cadr body))
+          (loc  (if (null? (cdr body)) () (cadr body)))
           (loc  (if (and (pair? loc) (eq? (car loc) 'line))
                     (list loc)
                     '()))

src/toplevel.c

@@ -115,6 +115,11 @@ jl_value_t *jl_eval_module_expr(jl_module_t *parent_module, jl_expr_t *ex)
     if (jl_array_len(ex->args) != 3 || !jl_is_expr(jl_exprarg(ex, 2))) {
         jl_error("syntax: malformed module expression");
     }
+
+    if (((jl_expr_t *)(jl_exprarg(ex, 2)))->head != jl_symbol("block")) {
+        jl_error("syntax: module expression third argument must be a block");
+    }
+
     int std_imports = (jl_exprarg(ex, 0) == jl_true);
     jl_sym_t *name = (jl_sym_t*)jl_exprarg(ex, 1);
     if (!jl_is_symbol(name)) {

test/syntax.jl

@@ -2224,6 +2224,17 @@ h35201(x; k=1) = (x, k)
 f35201(c) = h35201((;c...), k=true)
 @test f35201(Dict(:a=>1,:b=>3)) === ((a=1,b=3), true)
 
+
+@testset "issue #34544/35367" begin
+    # Test these evals shouldnt segfault
+    eval(Expr(:call, :eval, Expr(:quote, Expr(:module, true, :bar1, Expr(:block)))))
+    eval(Expr(:module, true, :bar2, Expr(:block)))
+    eval(Expr(:quote, Expr(:module, true, :bar3, Expr(:quote))))
+    @test_throws ErrorException eval(Expr(:call, :eval, Expr(:quote, Expr(:module, true, :bar4, Expr(:quote)))))
+    @test_throws ErrorException eval(Expr(:module, true, :bar5, Expr(:foo)))
+    @test_throws ErrorException eval(Expr(:module, true, :bar6, Expr(:quote)))
+end
+
 # issue #35391
 macro a35391(b)
     :(GC.@preserve ($(esc(b)),) )