C++: improvements to binary operator diagnostics (PR c++/87504)

The C frontend is able (where expression locations are available) to print
problems with binary operators in 3-location form, labelling the types of
the expressions:

  arg_0 op arg_1
  ~~~~~ ^~ ~~~~~
    |        |
    |        arg1 type
    arg0 type

The C++ frontend currently just shows the combined location:

  arg_0 op arg_1
  ~~~~~~^~~~~~~~

and fails to highlight where the subexpressions are, or their types.

This patch introduces a op_location_t struct for handling the above
operator-location vs combined-location split, and a new
class binary_op_rich_location for displaying the above, so that the
C++ frontend is able to use the more detailed 3-location form for
type mismatches in binary operators, and for -Wtautological-compare
(where types are not displayed).  Both forms can be seen in this
example:

bad-binary-ops.C:69:20: error: no match for 'operator&&' (operand types are
  's' and 't')
   69 |   return ns_4::foo && ns_4::inner::bar;
      |          ~~~~~~~~~ ^~ ~~~~~~~~~~~~~~~~
      |                |                   |
      |                s                   t
bad-binary-ops.C:69:20: note: candidate: 'operator&&(bool, bool)' <built-in>
   69 |   return ns_4::foo && ns_4::inner::bar;
      |          ~~~~~~~~~~^~~~~~~~~~~~~~~~~~~

The patch also allows for some uses of macros in
-Wtautological-compare, where both sides of the comparison have
been spelled the same way, e.g.:

Wtautological-compare-ranges.c:23:11: warning: self-comparison always
   evaluates to true [-Wtautological-compare]
   23 |   if (FOO == FOO);
      |           ^~

gcc/c-family/ChangeLog:
	PR c++/87504
	* c-common.h (warn_tautological_cmp): Convert 1st param from
	location_t to const op_location_t &.
	* c-warn.c (find_array_ref_with_const_idx_r): Call fold_for_warn
	when testing for INTEGER_CST.
	(warn_tautological_bitwise_comparison): Convert 1st param from
	location_t to const op_location_t &; use it to build a
	binary_op_rich_location, and use this.
	(spelled_the_same_p): New function.
	(warn_tautological_cmp): Convert 1st param from location_t to
	const op_location_t &.  Warn for macro expansions if
	spelled_the_same_p.  Use binary_op_rich_location.

gcc/c/ChangeLog:
	PR c++/87504
	* c-typeck.c (class maybe_range_label_for_tree_type_mismatch):
	Move from here to gcc-rich-location.h and gcc-rich-location.c.
	(build_binary_op): Use struct op_location_t and
	class binary_op_rich_location.

gcc/cp/ChangeLog:
	PR c++/87504
	* call.c (op_error): Convert 1st param from location_t to
	const op_location_t &.  Use binary_op_rich_location for binary
	ops.
	(build_conditional_expr_1): Convert 1st param from location_t to
	const op_location_t &.
	(build_conditional_expr): Likewise.
	(build_new_op_1): Likewise.
	(build_new_op): Likewise.
	* cp-tree.h (build_conditional_expr): Likewise.
	(build_new_op): Likewise.
	(build_x_binary_op): Likewise.
	(cp_build_binary_op): Likewise.
	* parser.c (cp_parser_primary_expression): Build a location
	for id-expression nodes.
	(cp_parser_binary_expression): Use an op_location_t when
	calling build_x_binary_op.
	(cp_parser_operator): Build a location for user-defined literals.
	* typeck.c (build_x_binary_op): Convert 1st param from location_t
	to const op_location_t &.
	(cp_build_binary_op): Likewise.  Use binary_op_rich_location.

gcc/ChangeLog:
	PR c++/87504
	* gcc-rich-location.c
	(maybe_range_label_for_tree_type_mismatch::get_text): Move here from
	c/c-typeck.c.
	(binary_op_rich_location::binary_op_rich_location): New ctor.
	(binary_op_rich_location::use_operator_loc_p): New function.
	* gcc-rich-location.h
	(class maybe_range_label_for_tree_type_mismatch)): Move here from
	c/c-typeck.c.
	(struct op_location_t): New forward decl.
	(class binary_op_rich_location): New class.
	* tree.h (struct op_location_t): New struct.

gcc/testsuite/ChangeLog:
	* c-c++-common/Wtautological-compare-ranges.c: New test.
	* g++.dg/cpp0x/pr51420.C: Add -fdiagnostics-show-caret and update
	expected output.
	* g++.dg/diagnostic/bad-binary-ops.C: Update expected output from
	1-location form to 3-location form, with labelling of ranges with
	types.  Add examples of id-expression nodes with namespaces.
	* g++.dg/diagnostic/param-type-mismatch-2.C: Likewise.

From-SVN: r267273

1 files changed, 49 insertions, 0 deletions

diff --git a/gcc/tree.h b/gcc/tree.h
index ab928ca..ed37e54 100644
--- a/gcc/tree.h
+++ b/gcc/tree.h
@@ -5962,4 +5962,53 @@ fndecl_built_in_p (const_tree node, built_in_function name)
 	  && DECL_FUNCTION_CODE (node) == name);
 }
 
+/* A struct for encapsulating location information about an operator
+   and the operation built from it.
+
+   m_operator_loc is the location of the operator
+   m_combined_loc is the location of the compound expression.
+
+   For example, given "a && b" the, operator location is:
+      a && b
+        ^~
+   and the combined location is:
+      a && b
+      ~~^~~~
+   Capturing this information allows for class binary_op_rich_location
+   to provide detailed information about e.g. type mismatches in binary
+   operations where enough location information is available:
+
+     arg_0 op arg_1
+     ~~~~~ ^~ ~~~~~
+       |        |
+       |        arg1 type
+       arg0 type
+
+   falling back to just showing the combined location:
+
+     arg_0 op arg_1
+     ~~~~~~^~~~~~~~
+
+   where it is not.  */
+
+struct op_location_t
+{
+  location_t m_operator_loc;
+  location_t m_combined_loc;
+
+  /* 1-argument ctor, for constructing from a combined location.  */
+  op_location_t (location_t combined_loc)
+  : m_operator_loc (UNKNOWN_LOCATION), m_combined_loc (combined_loc)
+  {}
+
+  /* 2-argument ctor, for distinguishing between the operator's location
+     and the combined location.  */
+  op_location_t (location_t operator_loc, location_t combined_loc)
+  : m_operator_loc (operator_loc), m_combined_loc (combined_loc)
+  {}
+
+  /* Implicitly convert back to a location_t, using the combined location.  */
+  operator location_t () const { return m_combined_loc; }
+};
+
 #endif  /* GCC_TREE_H  */