Ensure syntax error locations appear in backtraces (JuliaLang#31881)

Errors which are thrown directly inside jl_toplevel_eval_flex do not get
an entry in the backtrace. The most prominent of these are syntax
errors, but there's other cases too.

Fix this by constructing a julia expression throwing the appropriate
error, and evaling it to generate a julia-level frame.

src/julia.h

@@ -1430,6 +1430,8 @@ JL_DLLEXPORT jl_sym_t *jl_get_ARCH(void);
 JL_DLLEXPORT jl_value_t *jl_environ(int i);
 
 // throwing common exceptions
+JL_DLLEXPORT jl_value_t *jl_vexceptionf(jl_datatype_t *exception_type,
+ const char *fmt, va_list args);
 JL_DLLEXPORT void JL_NORETURN jl_error(const char *str);
 JL_DLLEXPORT void JL_NORETURN jl_errorf(const char *fmt, ...);
 JL_DLLEXPORT void JL_NORETURN jl_exceptionf(jl_datatype_t *ty,

src/rtutils.c

@@ -43,8 +43,8 @@ JL_DLLEXPORT void JL_NORETURN jl_error(const char *str)
 
 extern int vasprintf(char **str, const char *fmt, va_list ap);
 
-static jl_value_t *jl_vexceptionf(jl_datatype_t *exception_type,
-  const char *fmt, va_list args)
+jl_value_t *jl_vexceptionf(jl_datatype_t *exception_type,
+ const char *fmt, va_list args)
 {
  if (exception_type == NULL) {
  jl_printf(JL_STDERR, "ERROR: ");

src/toplevel.c

@@ -20,6 +20,7 @@
 #include "uv.h"
 #include "julia_assert.h"
 #include "intrinsics.h"
+#include "builtin_proto.h"
 
 #ifdef __cplusplus
 extern "C" {
@@ -568,6 +569,22 @@ static jl_module_t *eval_import_from(jl_module_t *m JL_PROPAGATES_ROOT, jl_expr_
  return NULL;
 }
 
+// Format msg and eval `throw(ErrorException(msg)))` in module `m`.
+// Used in `jl_toplevel_eval_flex` instead of `jl_errorf` so that the error
+// location in julia code gets into the backtrace.
+static void jl_eval_errorf(jl_module_t *m, const char* fmt, ...)
+{
+ jl_value_t *throw_ex = (jl_value_t*)jl_exprn(call_sym, 2);
+ JL_GC_PUSH1(&throw_ex);
+ jl_exprargset(throw_ex, 0, jl_builtin_throw);
+ va_list args;
+ va_start(args, fmt);
+ jl_exprargset(throw_ex, 1, jl_vexceptionf(jl_errorexception_type, fmt, args));
+ va_end(args);
+ jl_toplevel_eval_flex(m, throw_ex, 0, 0);
+ JL_GC_POP();
+}
+
 jl_value_t *jl_toplevel_eval_flex(jl_module_t *JL_NONNULL m, jl_value_t *e, int fast, int expanded)
 {
  jl_ptls_t ptls = jl_get_ptls_states();
@@ -585,7 +602,7 @@ jl_value_t *jl_toplevel_eval_flex(jl_module_t *JL_NONNULL m, jl_value_t *e, int
  char *n = jl_symbol_name((jl_sym_t*)e), *n0 = n;
  while (*n == '_') ++n;
  if (*n == 0 && n > n0)
- jl_error("all-underscore identifier used as rvalue");
+ jl_eval_errorf(m, "all-underscore identifier used as rvalue");
  }
  return jl_interpret_toplevel_expr_in(m, e, NULL, NULL);
  }
@@ -594,7 +611,7 @@ jl_value_t *jl_toplevel_eval_flex(jl_module_t *JL_NONNULL m, jl_value_t *e, int
 
  if (ex->head == dot_sym) {
  if (jl_expr_nargs(ex) != 2)
- jl_error("syntax: malformed \".\" expression");
+ jl_eval_errorf(m, "syntax: malformed \".\" expression");
  jl_value_t *lhs = jl_exprarg(ex, 0);
  jl_value_t *rhs = jl_exprarg(ex, 1);
  // only handle `a.b` syntax here, so qualified names can be eval'd in pure contexts
@@ -604,7 +621,7 @@ jl_value_t *jl_toplevel_eval_flex(jl_module_t *JL_NONNULL m, jl_value_t *e, int
  }
 
  if (ptls->in_pure_callback) {
- jl_error("eval cannot be used in a generated function");
+ jl_eval_errorf(m, "eval cannot be used in a generated function");
  }
 
  jl_method_instance_t *li = NULL;
@@ -646,7 +663,8 @@ jl_value_t *jl_toplevel_eval_flex(jl_module_t *JL_NONNULL m, jl_value_t *e, int
  }
  else {
  if (!jl_is_module(u))
- jl_errorf("invalid using path: \"%s\" does not name a module", jl_symbol_name(name));
+ jl_eval_errorf(m, "invalid using path: \"%s\" does not name a module",
+ jl_symbol_name(name));
  // `using A.B` syntax
  jl_module_using(m, u);
  if (m == jl_main_module && name == NULL) {
@@ -657,7 +675,7 @@ jl_value_t *jl_toplevel_eval_flex(jl_module_t *JL_NONNULL m, jl_value_t *e, int
  }
  }
  else {
- jl_error("syntax: malformed \"using\" statement");
+ jl_eval_errorf(m, "syntax: malformed \"using\" statement");
  }
  }
  JL_GC_POP();
@@ -684,7 +702,7 @@ jl_value_t *jl_toplevel_eval_flex(jl_module_t *JL_NONNULL m, jl_value_t *e, int
  }
  }
  else {
- jl_error("syntax: malformed \"import\" statement");
+ jl_eval_errorf(m, "syntax: malformed \"import\" statement");
  }
  }
  JL_GC_POP();
@@ -694,7 +712,7 @@ jl_value_t *jl_toplevel_eval_flex(jl_module_t *JL_NONNULL m, jl_value_t *e, int
  for (size_t i = 0; i < jl_array_len(ex->args); i++) {
  jl_sym_t *name = (jl_sym_t*)jl_array_ptr_ref(ex->args, i);
  if (!jl_is_symbol(name))
- jl_error("syntax: malformed \"export\" statement");
+ jl_eval_errorf(m, "syntax: malformed \"export\" statement");
  jl_module_export(m, name);
  }
  JL_GC_POP();
@@ -750,9 +768,9 @@ jl_value_t *jl_toplevel_eval_flex(jl_module_t *JL_NONNULL m, jl_value_t *e, int
  }
  else if (head == error_sym || head == jl_incomplete_sym) {
  if (jl_expr_nargs(ex) == 0)
- jl_errorf("malformed \"%s\" expression", jl_symbol_name(head));
+ jl_eval_errorf(m, "malformed \"%s\" expression", jl_symbol_name(head));
  if (jl_is_string(jl_exprarg(ex, 0)))
- jl_errorf("syntax: %s", jl_string_data(jl_exprarg(ex, 0)));
+ jl_eval_errorf(m, "syntax: %s", jl_string_data(jl_exprarg(ex, 0)));
  jl_throw(jl_exprarg(ex, 0));
  }
  else if (jl_is_symbol(ex)) {

test/backtrace.jl

@@ -189,3 +189,34 @@ let bt, found = false
  end
  @test found
 end
+
+# Syntax error locations appear in backtraces
+let trace = try
+ include_string(@__MODULE__,
+ """
+
+ )
+
+ """, "a_filename")
+ catch
+ stacktrace(Base.catch_stack()[end-1][2]) # Ignore LoadError
+ end
+ @test trace[1].func == Symbol("top-level scope")
+ @test trace[1].file == :a_filename
+ @test trace[1].line == 2
+end
+let trace = try
+ include_string(@__MODULE__,
+ """
+
+ incomplete_syntax(
+
+ """, "a_filename")
+ catch
+ stacktrace(Base.catch_stack()[end-1][2]) # Ignore LoadError
+ end
+ @test trace[1].func == Symbol("top-level scope")
+ @test trace[1].file == :a_filename
+ @test trace[1].line == 2
+end
+