diagnose comparisons between two arrays (P2865), fix for [GH #370]

src/error_msg.txt

@@ -3679,5 +3679,7 @@ ec_exp_interpolator;;"expected an interpolator (\"\\[\", \"\\[:\", \"\\{\", \"\\
 ec_interpolated_id_is_not_identifier;;"%sq does not spell an identifier"
 ec_interpolated_operand_is_not_token_sequence;;"the operand of a \"\\{...}\" interpolator is not a token sequence"
 ec_tag_redefined_differently;;"this declaration of %n does not declare the same type as the declaration %p"
+ec_array_comparison_deprecated;;"comparison between two arrays is deprecated"
+ec_array_comparison_not_allowed;;"comparison between two arrays is not allowed"
  ###############################################################################
 

src/expr.c

@@ -32399,6 +32399,30 @@ different enum types (or, in C, have different affiliated enum types).
 }  /* diagnose_comparison_if_different_enum_types */
 
 
+static void check_for_array_comparison(an_operand         *opnd1,
+                                       an_operand         *opnd2,
+                                       a_source_position  *operator_pos)
+/*
+opnd1 and opnd2 are the operands of a built-in equality or relational
+operator at operator_pos, before the array-to-pointer conversion.  If both
+have array type, issue a diagnostic: such comparisons are deprecated in C++20
+and not allowed in C++26 (P2865).
+*/
+{
+  if (cpp20_mode && is_array_type(opnd1->type) &&
+      is_array_type(opnd2->type)) {
+    if (cpp26_mode && !gpp_version_is(<150000) &&
+        !clangcpp_version_is(<200000)) {
+      /* GCC 15 and Clang 20 implement P2865.  Earlier versions only issue a
+         deprecation warning. */
+      expr_pos_error(ec_array_comparison_not_allowed, operator_pos);
+    } else {
+      expr_pos_warning(ec_array_comparison_deprecated, operator_pos);
+    }  /* if */
+  }  /* if */
+}  /* check_for_array_comparison */
+
+
 static void process_rel_operator(an_operand               *opnd1,
                                  an_operand               *opnd2,
                                  a_token_kind             operator_token,
@@ -32444,6 +32468,7 @@ describe the location of the operator.
   }  /* if */
   if (!processed) {
     /* Non-operator-function cases. */
+    check_for_array_comparison(opnd1, opnd2, operator_pos);
     /* The first operand must be an arithmetic or enum type or a pointer. */
     do_operand_transformations(opnd1, TOPT_NO_OPTIONS);
     opnd1_is_pointer = FALSE;
@@ -32948,6 +32973,7 @@ operator_tsn describe the location of the operator.
   }  /* if */
   if (!processed) {
     /* Non-operator-function cases. */
+    check_for_array_comparison(opnd1, opnd2, operator_pos);
     /* The first operand must be an arithmetic or enum type or a pointer. */
     do_operand_transformations(opnd1, TOPT_NO_OPTIONS);
     if (is_arithmetic_or_enum_type(opnd1->type)) {

src/pending_changes/gh-370-array-comparisons.txt

@@ -0,0 +1,12 @@
+[GH #370]
+C++26: comparison between two arrays is not allowed
+
+A comparison between two arrays using an equality or relational operator is
+deprecated in C++20 and not allowed in C++26 (P2865).  The front end did not
+diagnose it.  It is now a warning in C++20 and C++23, and an error in C++26
+(only a warning when emulating GCC versions before 15 or Clang versions before
+20, which do the same).  For example, with --c++26:
+
+  int a[2], b[2];
+  bool x = a == b;   // Now an error.
+  bool y = a == &b[0];  // Okay: one operand is a pointer.

tests/expectations/edg_x86_64/imported.log

@@ -1443,7 +1443,6 @@ clang/cpp/SemaCXX/vtordisp-mode.sft.cpp:fp:-DTEST_NUMBER=3 --c++11 -DVTORDISP_MO
 clang/cpp/SemaCXX/warn-array-comparion.sft.cpp:fn:-DTEST_NUMBER=1 --c++17:FAIL:
 clang/cpp/SemaCXX/warn-array-comparion.sft.cpp:fn:-DTEST_NUMBER=2 --c++20:FAIL:
 clang/cpp/SemaCXX/warn-array-comparion.sft.cpp:fn:-DTEST_NUMBER=3 --c++20:FAIL:
-clang/cpp/SemaCXX/warn-array-comparion.sft.cpp:fn:-DTEST_NUMBER=4 --c++26:FAIL:
 clang/cpp/SemaCXX/warn-bool-conversion.sft.cpp:fn:-DTEST_NUMBER=1 --c++03:FAIL:
 clang/cpp/SemaCXX/warn-cast-function-type-strict.sft.cpp:fp:-DTEST_NUMBER=1:FAIL:
 clang/cpp/SemaCXX/warn-cast-function-type.sft.cpp:fp:-DTEST_NUMBER=1:FAIL:
@@ -1455,7 +1454,6 @@ clang/cpp/SemaCXX/warn-memsize-comparison.sft.cpp:fn:-DTEST_NUMBER=1:FAIL:
 clang/cpp/SemaCXX/warn-nrvo.sft.cpp:fp:-DTEST_NUMBER=1:FAIL:
 clang/cpp/SemaCXX/warn-self-comparisons.sft.cpp:fn:-DTEST_NUMBER=1 --c++17:FAIL:
 clang/cpp/SemaCXX/warn-self-comparisons.sft.cpp:fn:-DTEST_NUMBER=2 --c++20:FAIL:
-clang/cpp/SemaCXX/warn-self-comparisons.sft.cpp:fn:-DTEST_NUMBER=3 --c++26:FAIL:
 clang/cpp/SemaCXX/warn-static-const-float.sft.cpp:fn:-DTEST_NUMBER=1 --c++03 -DEXT --c++03 -DNONE --c++03 -DNONE --c++03 -DNONE:FAIL:
 clang/cpp/SemaCXX/warn-static-const-float.sft.cpp:fn:-DTEST_NUMBER=2 --c++11 -DERR:FAIL:
 clang/cpp/SemaCXX/warn-static-const-float.sft.cpp:fn:-DTEST_NUMBER=3 --c++11 -DERR:FAIL:

tests/tests/changes/.GH370.rto/default.1.1.txt

@@ -0,0 +1,18 @@
+fe_only -DTEST_NUMBER=1 --c++26 Test_name.c
+"Test_name.c", line 10: error: comparison between two arrays is not allowed
+  bool x1 = a == b;  // Two arrays: diagnosed.
+              ^
+
+"Test_name.c", line 11: error: comparison between two arrays is not allowed
+  bool x2 = a != b;
+              ^
+
+"Test_name.c", line 12: error: comparison between two arrays is not allowed
+  bool x3 = a < b;
+              ^
+
+"Test_name.c", line 13: error: comparison between two arrays is not allowed
+  bool x4 = a >= b;
+              ^
+
+4 errors detected in the compilation of "Test_name.c".

tests/tests/changes/.GH370.rto/default.2.1.txt

@@ -0,0 +1,18 @@
+fe_only -DTEST_NUMBER=2 --c++26 --gnu_version 150000 Test_name.c
+"Test_name.c", line 10: error: comparison between two arrays is not allowed
+  bool x1 = a == b;  // Two arrays: diagnosed.
+              ^
+
+"Test_name.c", line 11: error: comparison between two arrays is not allowed
+  bool x2 = a != b;
+              ^
+
+"Test_name.c", line 12: error: comparison between two arrays is not allowed
+  bool x3 = a < b;
+              ^
+
+"Test_name.c", line 13: error: comparison between two arrays is not allowed
+  bool x4 = a >= b;
+              ^
+
+4 errors detected in the compilation of "Test_name.c".

tests/tests/changes/.GH370.rto/default.3.1.txt

@@ -0,0 +1,18 @@
+fe_only -DTEST_NUMBER=3 --c++26 --clang_version 200000 Test_name.c
+"Test_name.c", line 10: error: comparison between two arrays is not allowed
+  bool x1 = a == b;  // Two arrays: diagnosed.
+              ^
+
+"Test_name.c", line 11: error: comparison between two arrays is not allowed
+  bool x2 = a != b;
+              ^
+
+"Test_name.c", line 12: error: comparison between two arrays is not allowed
+  bool x3 = a < b;
+              ^
+
+"Test_name.c", line 13: error: comparison between two arrays is not allowed
+  bool x4 = a >= b;
+              ^
+
+4 errors detected in the compilation of "Test_name.c".

tests/tests/changes/.GH370_a.rto/default.1.1.txt

@@ -0,0 +1,17 @@
+fe_only -DTEST_NUMBER=1 --c++20 Test_name.c
+"Test_name.c", line 12: warning: comparison between two arrays is deprecated
+  bool x1 = a == b;  // Two arrays: diagnosed.
+              ^
+
+"Test_name.c", line 13: warning: comparison between two arrays is deprecated
+  bool x2 = a != b;
+              ^
+
+"Test_name.c", line 14: warning: comparison between two arrays is deprecated
+  bool x3 = a < b;
+              ^
+
+"Test_name.c", line 15: warning: comparison between two arrays is deprecated
+  bool x4 = a >= b;
+              ^
+

tests/tests/changes/.GH370_a.rto/default.2.1.txt

@@ -0,0 +1,17 @@
+fe_only -DTEST_NUMBER=2 --c++26 --gnu_version 140000 Test_name.c
+"Test_name.c", line 12: warning: comparison between two arrays is deprecated
+  bool x1 = a == b;  // Two arrays: diagnosed.
+              ^
+
+"Test_name.c", line 13: warning: comparison between two arrays is deprecated
+  bool x2 = a != b;
+              ^
+
+"Test_name.c", line 14: warning: comparison between two arrays is deprecated
+  bool x3 = a < b;
+              ^
+
+"Test_name.c", line 15: warning: comparison between two arrays is deprecated
+  bool x4 = a >= b;
+              ^
+

tests/tests/changes/.GH370_a.rto/default.3.1.txt

@@ -0,0 +1,17 @@
+fe_only -DTEST_NUMBER=3 --c++26 --clang_version 190000 Test_name.c
+"Test_name.c", line 12: warning: comparison between two arrays is deprecated
+  bool x1 = a == b;  // Two arrays: diagnosed.
+              ^
+
+"Test_name.c", line 13: warning: comparison between two arrays is deprecated
+  bool x2 = a != b;
+              ^
+
+"Test_name.c", line 14: warning: comparison between two arrays is deprecated
+  bool x3 = a < b;
+              ^
+
+"Test_name.c", line 15: warning: comparison between two arrays is deprecated
+  bool x4 = a >= b;
+              ^
+

tests/tests/changes/.GH370_a.rto/default.4.1.txt

@@ -0,0 +1 @@
+fe_only -DTEST_NUMBER=4 --c++17 Test_name.c

tests/tests/changes/GH370.sft.cpp

@@ -0,0 +1,16 @@
+//type:fn
+//options:--c++26:--c++26 --gnu_version 150000:--c++26 --clang_version 200000
+//remark:[GH #370] C++26: comparison between two arrays is not allowed
+//
+// P2865 makes a comparison between two arrays ill-formed in C++26.
+
+int a[2], b[2];
+int *p = b;
+
+bool x1 = a == b;  // Two arrays: diagnosed.
+bool x2 = a != b;
+bool x3 = a < b;
+bool x4 = a >= b;
+
+bool y1 = a == p;  // Array and pointer: not diagnosed.
+bool y2 = p < a;

tests/tests/changes/GH370_a.sft.cpp

@@ -0,0 +1,18 @@
+//type:fp
+//options:--c++20:--c++26 --gnu_version 140000:--c++26 --clang_version 190000:--c++17
+//remark:[GH #370] Comparison between two arrays is deprecated in C++20
+//
+// A comparison between two arrays is deprecated in C++20 and C++23.  When
+// emulating GCC before 15 or Clang before 20, it is also only deprecated in
+// C++26.  Before C++20 it is not diagnosed.
+
+int a[2], b[2];
+int *p = b;
+
+bool x1 = a == b;  // Two arrays: diagnosed.
+bool x2 = a != b;
+bool x3 = a < b;
+bool x4 = a >= b;
+
+bool y1 = a == p;  // Array and pointer: not diagnosed.
+bool y2 = p < a;

tests/tests/imported/clang/cpp/SemaCXX/.deprecated.rto/default.8.1.txt

@@ -164,6 +164,26 @@ fe_only -DTEST_NUMBER=8 --clang -tused -e 200 --no_wrap_diagnostics --clang_vers
     void trex(volatile short left_arm, volatile struct amber right_arm);
                                        ^
 
+"SemaCXX/deprecated.cpp", line 256: warning: comparison between two arrays is deprecated
+    bool b1 = arr1 == arr2;
+                   ^
+
+"SemaCXX/deprecated.cpp", line 258: warning: comparison between two arrays is deprecated
+    bool b2 = arr1 < arr2;
+                   ^
+
+"SemaCXX/deprecated.cpp", line 261: warning: comparison between two arrays is deprecated
+    bool b3 = arr1 == arr3;
+                   ^
+
+"SemaCXX/deprecated.cpp", line 262: warning: comparison between two arrays is deprecated
+    bool b4 = arr1 < arr3;
+                   ^
+
+"SemaCXX/deprecated.cpp", line 268: warning: comparison between two arrays is deprecated
+    bool b6 = arr1 == f();
+                   ^
+
 "SemaCXX/deprecated.cpp", line 280: warning: parameter "x" was set but never used
   [[deprecated]] void f2([[deprecated]] int x) {
                                             ^

tests/tests/imported/clang/cpp/SemaCXX/.deprecated.rto/default.9.1.txt

@@ -152,6 +152,26 @@ fe_only -DTEST_NUMBER=9 --clang -tused -e 200 --no_wrap_diagnostics --clang_vers
     void trex(volatile short left_arm, volatile struct amber right_arm);
                                        ^
 
+"SemaCXX/deprecated.cpp", line 256: warning: comparison between two arrays is deprecated
+    bool b1 = arr1 == arr2;
+                   ^
+
+"SemaCXX/deprecated.cpp", line 258: warning: comparison between two arrays is deprecated
+    bool b2 = arr1 < arr2;
+                   ^
+
+"SemaCXX/deprecated.cpp", line 261: warning: comparison between two arrays is deprecated
+    bool b3 = arr1 == arr3;
+                   ^
+
+"SemaCXX/deprecated.cpp", line 262: warning: comparison between two arrays is deprecated
+    bool b4 = arr1 < arr3;
+                   ^
+
+"SemaCXX/deprecated.cpp", line 268: warning: comparison between two arrays is deprecated
+    bool b6 = arr1 == f();
+                   ^
+
 "SemaCXX/deprecated.cpp", line 280: warning: parameter "x" was set but never used
   [[deprecated]] void f2([[deprecated]] int x) {
                                             ^

tests/tests/imported/clang/cpp/SemaCXX/.self-comparison.rto/default.1.1.txt

@@ -1,4 +1,16 @@
 fe_only -DTEST_NUMBER=1 --clang -tused -e 200 --no_wrap_diagnostics --clang_version 999999 --c++20 Test_name.c
+"Test_name.c", line 21: warning: comparison between two arrays is deprecated
+    bool h() { return a == b; } // expected-warning {{array comparison always evaluates to false}} expected-warning {{deprecated}}
+                        ^
+
+"Test_name.c", line 24: warning: comparison between two arrays is deprecated
+      return a == c; // expected-warning {{array comparison always evaluates to false}} expected-warning {{deprecated}}
+               ^
+
+"Test_name.c", line 30: warning: comparison between two arrays is deprecated
+  bool k = NA::x == NB::x; // expected-warning {{self-comparison always evaluates to true}} expected-warning {{deprecated}}
+                 ^
+
 "Test_name.c", line 53: warning: statement is unreachable
       return static_field == static_field;  // expected-warning {{self-comparison always evaluates to true}}
       ^
@@ -39,6 +51,10 @@ fe_only -DTEST_NUMBER=1 --clang -tused -e 200 --no_wrap_diagnostics --clang_vers
     return s1.array == s1.array;  // expected-warning {{self-comparison always evaluates to true}} expected-warning {{deprecated}}
     ^
 
+"Test_name.c", line 87: warning: comparison between two arrays is deprecated
+    return s1.array == s1.array;  // expected-warning {{self-comparison always evaluates to true}} expected-warning {{deprecated}}
+                    ^
+
 "Test_name.c", line 88: warning: statement is unreachable
     return t.s.static_field == S::static_field;  // expected-warning {{self-comparison always evaluates to true}}
     ^
@@ -103,6 +119,10 @@ fe_only -DTEST_NUMBER=1 --clang -tused -e 200 --no_wrap_diagnostics --clang_vers
     return s2.array == s1.array; // FIXME: This always evaluates to false. expected-warning {{deprecated}}
     ^
 
+"Test_name.c", line 108: warning: comparison between two arrays is deprecated
+    return s2.array == s1.array; // FIXME: This always evaluates to false. expected-warning {{deprecated}}
+                    ^
+
 "Test_name.c", line 109: warning: statement is unreachable
     return s2.array[0] == s1.array[0];
     ^

tests/tests/imported/clang/cpp/SemaCXX/.self-comparison.rto/default.2.1.txt

@@ -1,4 +1,16 @@
 fe_only -DTEST_NUMBER=2 --clang -tused -e 200 --no_wrap_diagnostics --clang_version 999999 --c++20 Test_name.c
+"Test_name.c", line 21: warning: comparison between two arrays is deprecated
+    bool h() { return a == b; } // expected-warning {{array comparison always evaluates to false}} expected-warning {{deprecated}}
+                        ^
+
+"Test_name.c", line 24: warning: comparison between two arrays is deprecated
+      return a == c; // expected-warning {{array comparison always evaluates to false}} expected-warning {{deprecated}}
+               ^
+
+"Test_name.c", line 30: warning: comparison between two arrays is deprecated
+  bool k = NA::x == NB::x; // expected-warning {{self-comparison always evaluates to true}} expected-warning {{deprecated}}
+                 ^
+
 "Test_name.c", line 53: warning: statement is unreachable
       return static_field == static_field;  // expected-warning {{self-comparison always evaluates to true}}
       ^
@@ -39,6 +51,10 @@ fe_only -DTEST_NUMBER=2 --clang -tused -e 200 --no_wrap_diagnostics --clang_vers
     return s1.array == s1.array;  // expected-warning {{self-comparison always evaluates to true}} expected-warning {{deprecated}}
     ^
 
+"Test_name.c", line 87: warning: comparison between two arrays is deprecated
+    return s1.array == s1.array;  // expected-warning {{self-comparison always evaluates to true}} expected-warning {{deprecated}}
+                    ^
+
 "Test_name.c", line 88: warning: statement is unreachable
     return t.s.static_field == S::static_field;  // expected-warning {{self-comparison always evaluates to true}}
     ^
@@ -103,6 +119,10 @@ fe_only -DTEST_NUMBER=2 --clang -tused -e 200 --no_wrap_diagnostics --clang_vers
     return s2.array == s1.array; // FIXME: This always evaluates to false. expected-warning {{deprecated}}
     ^
 
+"Test_name.c", line 108: warning: comparison between two arrays is deprecated
+    return s2.array == s1.array; // FIXME: This always evaluates to false. expected-warning {{deprecated}}
+                    ^
+
 "Test_name.c", line 109: warning: statement is unreachable
     return s2.array[0] == s1.array[0];
     ^

tests/tests/imported/clang/cpp/SemaCXX/.warn-array-comparion.rto/default.2.1.txt

@@ -1 +1,13 @@
 fe_only -DTEST_NUMBER=2 --clang -tused -e 200 --no_wrap_diagnostics --clang_version 999999 --c++20 Test_name.c
+"Test_name.c", line 14: warning: comparison between two arrays is deprecated
+    if (obj1.str != obj2.str) // not-cxx20-warning {{comparison between two arrays compare their addresses}} cxx20-warning {{comparison between two arrays is deprecated}}
+                 ^
+
+"Test_name.c", line 16: warning: comparison between two arrays is deprecated
+    if (obj1.id != obj2.id) // not-cxx20-warning {{comparison between two arrays compare their addresses}} cxx20-warning {{comparison between two arrays is deprecated}}
+                ^
+
+"Test_name.c", line 23: warning: comparison between two arrays is deprecated
+    if (array1 == array2) { } // not-cxx20-warning {{comparison between two arrays compare their addresses}} cxx20-warning {{comparison between two arrays is deprecated}}
+               ^
+

tests/tests/imported/clang/cpp/SemaCXX/.warn-array-comparion.rto/default.3.1.txt

@@ -1 +1,13 @@
 fe_only -DTEST_NUMBER=3 --clang -tused -e 200 --no_wrap_diagnostics --clang_version 999999 --c++20 Test_name.c
+"Test_name.c", line 14: warning: comparison between two arrays is deprecated
+    if (obj1.str != obj2.str) // not-cxx20-warning {{comparison between two arrays compare their addresses}} cxx20-warning {{comparison between two arrays is deprecated}}
+                 ^
+
+"Test_name.c", line 16: warning: comparison between two arrays is deprecated
+    if (obj1.id != obj2.id) // not-cxx20-warning {{comparison between two arrays compare their addresses}} cxx20-warning {{comparison between two arrays is deprecated}}
+                ^
+
+"Test_name.c", line 23: warning: comparison between two arrays is deprecated
+    if (array1 == array2) { } // not-cxx20-warning {{comparison between two arrays compare their addresses}} cxx20-warning {{comparison between two arrays is deprecated}}
+               ^
+