[p4-constraints] Allow C++ compliant multi-line strings.

I.e. strings like:
```
  "This is the start of my string "
  "and this is the end."
```

This will help solve a C++ preprocessor issue we're having where it will randomly insert preprocessor directives into the `@entry_restriction` annotation string when using a single multi-line string.

PiperOrigin-RevId: 628166543

e2e_tests/invalid_constraints.expected.output

@@ -74,3 +74,15 @@ Type error: operand type optional<32> does not support ordered comparison
 102 |     ::unknown > 10;
     |     ^^^^^^^^^
 Type error: unknown attribute 'unknown'
+
+- e2e_tests/invalid_constraints.p4:113:1-9:
+    |       headers.ethernet.ether_type == 0x86DD;
+113 | ::unknown > 10;
+    | ^^^^^^^^^
+Type error: unknown attribute 'unknown'
+
+- e2e_tests/invalid_constraints.p4:157:5-13:
+    |     // An invalid constraint to ensure error messages are sensible.
+157 |     ::unknown > 10;
+    |     ^^^^^^^^^
+Type error: unknown attribute 'unknown'

e2e_tests/invalid_constraints.p4

@@ -103,6 +103,77 @@ control invalid_constraints(inout headers_t headers,
   ")
   table unknown_metadata { actions = {} key = {} }
 
+  @file(__FILE__)
+  @line(__LINE__)
+  @entry_restriction(
+    // Either wildcard or exact match (i.e., "optional" match).
+    "headers.ipv4.dst_addr::mask == 0 || headers.ipv4.dst_addr::mask == -1;"
+
+    // Only match on IPv4 addresses of IPv4 packets.
+    "headers.ipv4.dst_addr::mask != 0 ->     "
+    // Macros are not usable within a single-line string.
+    "  headers.ethernet.ether_type == 0x0800;"
+
+    // Only match on IPv6 addresses of IPv6 packets.
+    "headers.ipv6.dst_addr::mask != 0 ->
+      headers.ethernet.ether_type == IPv6_ETHER_TYPE;"
+
+    // An invalid constraint to ensure error messages are sensible.
+    "::unknown > 10;"
+
+    // More valid stuff.
+    "local_metadata.dscp::mask != 0 -> (
+      headers.ethernet.ether_type == IPv4_ETHER_TYPE ||
+      headers.ethernet.ether_type == IPv6_ETHER_TYPE ||
+      local_metadata.is_ip_packet == 1
+    );
+  ")
+  table invalid_vrf_classifier_table_with_multiline_strings {
+    key = {
+      headers.ethernet.ether_type : ternary;
+      headers.ipv4.dst_addr : ternary;
+      headers.ipv6.dst_addr : ternary;
+      local_metadata.dscp : ternary;
+      local_metadata.is_ip_packet : ternary;
+    }
+    actions = { }
+  }
+
+  @file(__FILE__)
+  @line(__LINE__)
+  @entry_restriction("
+    // Either wildcard or exact match (i.e., 'optional' match).
+    headers.ipv4.dst_addr::mask == 0 || headers.ipv4.dst_addr::mask == -1;
+
+    // Only match on IPv4 addresses of IPv4 packets.
+    headers.ipv4.dst_addr::mask != 0 ->
+      headers.ethernet.ether_type == 0x0800;
+
+    // Only match on IPv6 addresses of IPv6 packets.
+    headers.ipv6.dst_addr::mask != 0 ->
+      headers.ethernet.ether_type == IPv6_ETHER_TYPE;
+
+    // An invalid constraint to ensure error messages are sensible.
+    ::unknown > 10;
+
+    // More valid stuff.
+    local_metadata.dscp::mask != 0 -> (
+      headers.ethernet.ether_type == IPv4_ETHER_TYPE ||
+      headers.ethernet.ether_type == IPv6_ETHER_TYPE ||
+      local_metadata.is_ip_packet == 1
+    );
+  ")
+  table invalid_vrf_classifier_table_without_multiline_strings {
+    key = {
+      headers.ethernet.ether_type : ternary;
+      headers.ipv4.dst_addr : ternary;
+      headers.ipv6.dst_addr : ternary;
+      local_metadata.dscp : ternary;
+      local_metadata.is_ip_packet : ternary;
+    }
+    actions = { }
+  }
+
   apply {
     forgot_quotes.apply();
     forgot_quotes_with_srcloc.apply();
@@ -119,6 +190,8 @@ control invalid_constraints(inout headers_t headers,
     boolean_negation_of_integer.apply();
     optional_does_not_support_ordered_comparison.apply();
     unknown_metadata.apply();
+    invalid_vrf_classifier_table_with_multiline_strings.apply();
+    invalid_vrf_classifier_table_without_multiline_strings.apply();
    }
  }
 

e2e_tests/valid_constraints.expected.output

@@ -11,7 +11,7 @@ e2e_tests/table_entries/acl_table_1.pb.txt
 All entries must satisfy:
 
 e2e_tests/valid_constraints.p4:22:5-65:
-   |     // Either wildcard or exact match (i.e., " optional " match).
+   |     // Either wildcard or exact match (i.e., 'optional' match).
 22 |     hdr.ipv4.dst_addr::mask == 0 || hdr.ipv4.dst_addr::mask == -1;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
@@ -84,10 +84,10 @@ e2e_tests/table_entries/optional_match_table_invalid_1.pb.txt
 === Output ===
 All entries must satisfy:
 
-e2e_tests/valid_constraints.p4:62:5-32:
-   |     // A real constraint: only wildcard match is okay.
-62 |     hdr.ipv4.dst_addr::mask == 0;
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+e2e_tests/valid_constraints.p4:100:5-32:
+    |     // A real constraint: only wildcard match is okay.
+100 |     hdr.ipv4.dst_addr::mask == 0;
+    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 But your entry does not.
 >>>Relevant Entry Info<<<
@@ -107,10 +107,10 @@ e2e_tests/table_entries/optional_match_table_valid_max_priority.pb.txt
 === Output ===
 All entries must satisfy:
 
-e2e_tests/valid_constraints.p4:64:5-27:
-   |     // A constraint on metadata.
-64 |     ::priority < 0x7fffffff;
-   |     ^^^^^^^^^^^^^^^^^^^^^^^
+e2e_tests/valid_constraints.p4:102:5-27:
+    |     // A constraint on metadata.
+102 |     ::priority < 0x7fffffff;
+    |     ^^^^^^^^^^^^^^^^^^^^^^^
 
 But your entry does not.
 >>>Relevant Entry Info<<<

e2e_tests/valid_constraints.p4

@@ -18,7 +18,7 @@ control valid_constraints(inout headers_t hdr,
   @file(__FILE__)
   @line(__LINE__)
   @entry_restriction("
-    // Either wildcard or exact match (i.e., "optional" match).
+    // Either wildcard or exact match (i.e., 'optional' match).
     hdr.ipv4.dst_addr::mask == 0 || hdr.ipv4.dst_addr::mask == -1;
 
     // Only match on IPv4 addresses of IPv4 packets.
@@ -50,6 +50,44 @@ control valid_constraints(inout headers_t hdr,
     actions = { }
   }
 
+
+  @file(__FILE__)
+  @line(__LINE__)
+  // Tests that multiline strings also work.
+  @entry_restriction(
+    // Either wildcard or exact match (i.e., "optional" match).
+    "hdr.ipv4.dst_addr::mask == 0 || hdr.ipv4.dst_addr::mask == -1;"
+
+    // Only match on IPv4 addresses of IPv4 packets.
+    "hdr.ipv4.dst_addr::mask != 0 ->     "
+    // Macros are not usable within a single-line string.
+    "  hdr.ethernet.ether_type == 0x0800;"
+
+    // Only match on IPv6 addresses of IPv6 packets.
+    "hdr.ipv6.dst_addr::mask != 0 ->
+      hdr.ethernet.ether_type == IPv6_ETHER_TYPE;
+
+    local_metadata.dscp::mask != 0 -> (
+      hdr.ethernet.ether_type == IPv4_ETHER_TYPE ||
+      hdr.ethernet.ether_type == IPv6_ETHER_TYPE ||
+      local_metadata.is_ip_packet == 1
+    );
+  ")
+  @id(6)
+  table vrf_classifier_table_with_multiline_strings {
+    key = {
+      hdr.ethernet.ether_type : ternary;
+      hdr.ethernet.src_addr : ternary;
+      hdr.ipv4.dst_addr : ternary;
+      standard_metadata.ingress_port: ternary;
+      hdr.ipv6.dst_addr : ternary;
+      hdr.ipv4.src_addr : optional;
+      local_metadata.dscp : ternary;
+      local_metadata.is_ip_packet : ternary;
+    }
+    actions = { }
+  }
+
   @file(__FILE__)
   @line(__LINE__)
   @entry_restriction("
@@ -90,6 +128,7 @@ control valid_constraints(inout headers_t hdr,
     vrf_classifier_table.apply();
     optional_match_table.apply();
     network_address_table.apply();
+    vrf_classifier_table_with_multiline_strings.apply();
   }
 }
 

p4_constraints/backend/constraint_info.cc

@@ -24,11 +24,14 @@
 #include "absl/log/log.h"
 #include "absl/status/status.h"
 #include "absl/status/statusor.h"
+#include "absl/strings/match.h"
 #include "absl/strings/str_cat.h"
 #include "absl/strings/str_join.h"
 #include "absl/strings/string_view.h"
 #include "absl/strings/strip.h"
 #include "absl/types/optional.h"
+#include "gutils/source_location.h"
+#include "gutils/status_builder.h"
 #include "gutils/status_macros.h"
 #include "p4/config/v1/p4info.pb.h"
 #include "p4/config/v1/p4types.pb.h"
@@ -135,8 +138,45 @@ absl::StatusOr<absl::optional<ConstraintSource>> ExtractConstraint(
            << "Syntax error: @" << (is_table ? "entry" : "action")
            << "_restriction must be enclosed in '(\"' and '\")'";
   }
+
+  // Consume intermediate, matched double-quotes (") to allow constraints with
+  // the following shape (and similar for actions):
+  // ```p4
+  //   @entry_restriction(
+  //      "<constraint1>"
+  //      "<constraint2>"
+  //      ...
+  //   )
+  //   table foo { ... }
+  // ```
+  std::string constraint_string_without_quotes = std::string(constraint_string);
+  // Currently, the p4c frontend collapses all white space in annotations
+  // (like `@entry_restriction`) into a single space. See
+  // https://github.com/p4lang/p4c/issues/2333 for more information.
+  // Thus, rather than preserve the white space, we add a newline as an
+  // imperfect workaround to improve readability. The idea is that this form
+  // would most often be used for multi-line input.
+  RE2::GlobalReplace(&constraint_string_without_quotes, "\" \"", "\n");
+  // Ensure there are no further quotation marks in
+  // `constraint_string_without_quotes`, since those would always be incorrect.
+  if (absl::StrContains(constraint_string_without_quotes, "\"")) {
+    return gutils::InvalidArgumentErrorBuilder(GUTILS_LOC)
+           << "In "
+           << (constraint_kind == ConstraintKind::kTableConstraint ? "table "
+                                                                   : "action ")
+           << preamble.name() << ":\n"
+           << "Syntax error: @"
+           << (constraint_kind == ConstraintKind::kTableConstraint ? "entry"
+                                                                   : "action")
+           << "_restriction was parsed with unexpected quotation marks (\"). "
+              "Ensure you aren't using any quotation marks in a comment. "
+              "Otherwise, this suggests a parser assumption was violated, "
+              "likely due to a p4c frontend change, or "
+              "`@p4runtime_translation` support being added.";
+  }
+
   return ConstraintSource{
-      .constraint_string = std::string(constraint_string),
+      .constraint_string = std::move(constraint_string_without_quotes),
       .constraint_location = constraint_location,
   };
 }