lower top-level statements in such a way that the front-end knows

their values are not used

fixes most false positives in the deprecation for using the value of `.=`

src/ast.c

@@ -61,7 +61,7 @@ jl_sym_t *generated_only_sym;
 jl_sym_t *isdefined_sym; jl_sym_t *nospecialize_sym;
 jl_sym_t *macrocall_sym; jl_sym_t *colon_sym;
 jl_sym_t *hygienicscope_sym;
-jl_sym_t *escape_sym;
+jl_sym_t *escape_sym; jl_sym_t *block_sym;
 jl_sym_t *gc_preserve_begin_sym; jl_sym_t *gc_preserve_end_sym;
 jl_sym_t *throw_undef_if_not_sym;
 
@@ -385,6 +385,7 @@ void jl_init_frontend(void)
     generated_sym = jl_symbol("generated");
     generated_only_sym = jl_symbol("generated_only");
     throw_undef_if_not_sym = jl_symbol("throw_undef_if_not");
+    block_sym = jl_symbol("block");
 }
 
 JL_DLLEXPORT void jl_lisp_prompt(void)
@@ -829,7 +830,11 @@ jl_value_t *jl_parse_eval_all(const char *fname,
                     form = jl_expand_macros(form, inmodule, NULL, 0);
                     expression = julia_to_scm(fl_ctx, form);
                 }
-                expression = fl_applyn(fl_ctx, 1, symbol_value(symbol(fl_ctx, "jl-expand-to-thunk")), expression);
+                // expand non-final expressions in statement position (value unused)
+                expression =
+                    fl_applyn(fl_ctx, 1,
+                              symbol_value(symbol(fl_ctx, iscons(cdr_(ast)) ? "jl-expand-to-thunk-stmt" : "jl-expand-to-thunk")),
+                              expression);
             }
             jl_get_ptls_states()->world_age = jl_world_counter;
             form = scm_to_julia(fl_ctx, expression, inmodule);
@@ -1115,6 +1120,18 @@ JL_DLLEXPORT jl_value_t *jl_expand(jl_value_t *expr, jl_module_t *inmodule)
     return expr;
 }
 
+// expand in a context where the expression value is unused
+JL_DLLEXPORT jl_value_t *jl_expand_stmt(jl_value_t *expr, jl_module_t *inmodule)
+{
+    JL_TIMING(LOWERING);
+    JL_GC_PUSH1(&expr);
+    expr = jl_copy_ast(expr);
+    expr = jl_expand_macros(expr, inmodule, NULL, 0);
+    expr = jl_call_scm_on_ast("jl-expand-to-thunk-stmt", expr, inmodule);
+    JL_GC_POP();
+    return expr;
+}
+
 
 #ifdef __cplusplus
 }

src/jlfrontend.scm

@@ -94,12 +94,14 @@
 
 (define *in-expand* #f)
 
+(define (toplevel-only-expr? e)
+  (and (pair? e)
+       (or (memq (car e) '(toplevel line module import importall using export
+                                    error incomplete))
+           (and (eq? (car e) 'global) (every symbol? (cdr e))))))
+
 (define (expand-toplevel-expr e)
-  (cond ((or (atom? e)
-             (and (pair? e)
-                  (or (memq (car e) '(toplevel line module import importall using export
-                                               error incomplete))
-                      (and (eq? (car e) 'global) (every symbol? (cdr e))))))
+  (cond ((or (atom? e) (toplevel-only-expr? e))
          (if (underscore-symbol? e)
              (syntax-deprecation "underscores as an rvalue" "" #f))
          e)
@@ -207,6 +209,11 @@
   (parser-wrap (lambda ()
                  (expand-toplevel-expr expr))))
 
+(define (jl-expand-to-thunk-stmt expr)
+  (jl-expand-to-thunk (if (toplevel-only-expr? expr)
+                          expr
+                          `(block ,expr (null)))))
+
 ; run whole frontend on a string. useful for testing.
 (define (fe str)
   (expand-toplevel-expr (julia-parse str)))

src/julia.h

@@ -1450,6 +1450,7 @@ JL_DLLEXPORT jl_value_t *jl_parse_string(const char *str, size_t len,
 JL_DLLEXPORT jl_value_t *jl_load_file_string(const char *text, size_t len,
                                              char *filename, jl_module_t *inmodule);
 JL_DLLEXPORT jl_value_t *jl_expand(jl_value_t *expr, jl_module_t *inmodule);
+JL_DLLEXPORT jl_value_t *jl_expand_stmt(jl_value_t *expr, jl_module_t *inmodule);
 JL_DLLEXPORT jl_value_t *jl_eval_string(const char *str);
 
 // external libraries

src/julia_internal.h

@@ -1015,7 +1015,7 @@ extern jl_sym_t *compiler_temp_sym; extern jl_sym_t *foreigncall_sym;
 extern jl_sym_t *const_sym;   extern jl_sym_t *thunk_sym;
 extern jl_sym_t *underscore_sym; extern jl_sym_t *colon_sym;
 extern jl_sym_t *abstracttype_sym; extern jl_sym_t *primtype_sym;
-extern jl_sym_t *structtype_sym;
+extern jl_sym_t *structtype_sym; extern jl_sym_t *block_sym;
 extern jl_sym_t *global_sym; extern jl_sym_t *unused_sym;
 extern jl_sym_t *boundscheck_sym; extern jl_sym_t *inbounds_sym;
 extern jl_sym_t *copyast_sym; extern jl_sym_t *fastmath_sym;

src/toplevel.c

@@ -228,7 +228,7 @@ jl_value_t *jl_eval_module_expr(jl_module_t *parent_module, jl_expr_t *ex)
         for (int i = 0; i < jl_array_len(exprs); i++) {
             // process toplevel form
             ptls->world_age = jl_world_counter;
-            form = jl_expand(jl_array_ptr_ref(exprs, i), newm);
+            form = jl_expand_stmt(jl_array_ptr_ref(exprs, i), newm);
             ptls->world_age = jl_world_counter;
             (void)jl_toplevel_eval_flex(newm, form, 1, 1);
         }