c++: explain failing static_assert
While looking at another bug I wanted the compiler to tell me what the two unequal values were. gcc/cp/ChangeLog: * semantics.cc (find_failing_clause): Return expr if not decomposable. (finish_static_assert): Show constant values in failing comparison. gcc/testsuite/ChangeLog: * g++.dg/template/explicit-args6.C: Add expected message.
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2 changed files with 22 additions and 13 deletions
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@ -11062,9 +11062,10 @@ find_failing_clause_r (tree expr)
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static tree
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find_failing_clause (tree expr)
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{
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if (TREE_CODE (expr) != TRUTH_ANDIF_EXPR)
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return NULL_TREE;
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return find_failing_clause_r (expr);
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if (TREE_CODE (expr) == TRUTH_ANDIF_EXPR)
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if (tree e = find_failing_clause_r (expr))
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expr = e;
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return expr;
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}
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/* Build a STATIC_ASSERT for a static assertion with the condition
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@ -11134,9 +11135,9 @@ finish_static_assert (tree condition, tree message, location_t location,
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tree bad = find_failing_clause (orig_condition);
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/* If not, or its location is unusable, fall back to the previous
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location. */
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location_t cloc = location;
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if (cp_expr_location (bad) != UNKNOWN_LOCATION)
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cloc = cp_expr_location (bad);
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location_t cloc = cp_expr_loc_or_loc (bad, location);
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/* Nobody wants to see the artificial (bool) cast. */
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bad = tree_strip_nop_conversions (bad);
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/* Report the error. */
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if (len == 0)
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@ -11144,16 +11145,22 @@ finish_static_assert (tree condition, tree message, location_t location,
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else
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error_at (cloc, "static assertion failed: %s",
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TREE_STRING_POINTER (message));
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if (show_expr_p)
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inform (cloc, "%qE evaluates to false",
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/* Nobody wants to see the artificial (bool) cast. */
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(bad ? tree_strip_nop_conversions (bad) : orig_condition));
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/* Actually explain the failure if this is a concept check or a
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requires-expression. */
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if (concept_check_p (orig_condition)
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|| TREE_CODE (orig_condition) == REQUIRES_EXPR)
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diagnose_constraints (location, orig_condition, NULL_TREE);
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if (concept_check_p (bad)
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|| TREE_CODE (bad) == REQUIRES_EXPR)
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diagnose_constraints (location, bad, NULL_TREE);
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else if (COMPARISON_CLASS_P (bad)
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&& ARITHMETIC_TYPE_P (TREE_TYPE (TREE_OPERAND (bad, 0))))
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{
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tree op0 = fold_non_dependent_expr (TREE_OPERAND (bad, 0));
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tree op1 = fold_non_dependent_expr (TREE_OPERAND (bad, 1));
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tree cond = build2 (TREE_CODE (bad), boolean_type_node, op0, op1);
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inform (cloc, "the comparison reduces to %qE", cond);
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}
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else if (show_expr_p)
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inform (cloc, "%qE evaluates to false", bad);
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}
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else if (condition && condition != error_mark_node)
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{
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@ -20,6 +20,8 @@ constexpr unsigned
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frob()
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{
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static_assert(N == 1, "user-friendly diagnostic"); // { dg-error "user-friendly" }
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// dg-message { "-1 == 1" "" { target *-*-* } .-1 }
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// narrowing check, reject negative values
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return unsigned{N}; // { dg-prune-output "narrowing" }
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} // { dg-prune-output "flows off the end" }
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