From c4c5cdc1f595e5177ec7fe3164a644aa19f9a783 Mon Sep 17 00:00:00 2001
From: Jon Meow <46229924+jonmeow@users.noreply.github.com>
Date: Thu, 3 Mar 2022 10:21:38 -0800
Subject: [PATCH] Replace is_sorted with comparison (#1104)

* Replace is_sorted with comparison

* Switch to StringRefContainsPointer
---
 common/string_helpers.cpp            | 7 ++++++-
 common/string_helpers.h              | 5 +++++
 toolchain/lexer/BUILD                | 2 ++
 toolchain/lexer/test_helpers.h       | 3 ++-
 toolchain/lexer/tokenized_buffer.cpp | 4 ++--
 5 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/common/string_helpers.cpp b/common/string_helpers.cpp
index 2d66f4dae345..f9b9147f4da3 100644
--- a/common/string_helpers.cpp
+++ b/common/string_helpers.cpp
@@ -13,7 +13,7 @@
 
 namespace Carbon {
 
-static constexpr llvm::StringRef TripleQuotes = "\"\"\"";
+static constexpr llvm::StringRef TripleQuotes = R"(""")";
 static constexpr llvm::StringRef HorizontalWhitespaceChars = " \t";
 
 // Carbon only takes uppercase hex input.
@@ -169,4 +169,9 @@ auto ParseBlockStringLiteral(llvm::StringRef source)
   return parsed;
 }
 
+auto StringRefContainsPointer(llvm::StringRef ref, const char* ptr) -> bool {
+  auto le = std::less_equal<const char*>();
+  return le(ref.begin(), ptr) && le(ptr, ref.end());
+}
+
 }  // namespace Carbon
diff --git a/common/string_helpers.h b/common/string_helpers.h
index 79d07fea5432..1b0a79911da8 100644
--- a/common/string_helpers.h
+++ b/common/string_helpers.h
@@ -26,6 +26,11 @@ auto UnescapeStringLiteral(llvm::StringRef source, bool is_block_string = false)
 auto ParseBlockStringLiteral(llvm::StringRef source)
     -> llvm::Expected<std::string>;
 
+// Returns true if the pointer is in the string ref (including equality with
+// `ref.end()`). This should be used instead of `<=` comparisons for
+// correctness.
+auto StringRefContainsPointer(llvm::StringRef ref, const char* ptr) -> bool;
+
 }  // namespace Carbon
 
 #endif  // COMMON_STRING_HELPERS_H_
diff --git a/toolchain/lexer/BUILD b/toolchain/lexer/BUILD
index c701956024c4..7dfe303d272d 100644
--- a/toolchain/lexer/BUILD
+++ b/toolchain/lexer/BUILD
@@ -40,6 +40,7 @@ cc_library(
     hdrs = ["test_helpers.h"],
     deps = [
         "//common:check",
+        "//common:string_helpers",
         "//toolchain/diagnostics:diagnostic_emitter",
         "@com_google_googletest//:gtest",
         "@llvm-project//llvm:Support",
@@ -160,6 +161,7 @@ cc_library(
         ":token_kind",
         "//common:check",
         "//common:ostream",
+        "//common:string_helpers",
         "//toolchain/diagnostics:diagnostic_emitter",
         "//toolchain/source:source_buffer",
         "@llvm-project//llvm:Support",
diff --git a/toolchain/lexer/test_helpers.h b/toolchain/lexer/test_helpers.h
index f66cfdd64103..f47abc612b89 100644
--- a/toolchain/lexer/test_helpers.h
+++ b/toolchain/lexer/test_helpers.h
@@ -11,6 +11,7 @@
 #include <string>
 
 #include "common/check.h"
+#include "common/string_helpers.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/Support/FormatVariadic.h"
 #include "toolchain/diagnostics/diagnostic_emitter.h"
@@ -28,7 +29,7 @@ class SingleTokenDiagnosticTranslator
       : token_(token) {}
 
   auto GetLocation(const char* pos) -> Diagnostic::Location override {
-    CHECK(llvm::is_sorted(std::array{token_.begin(), pos, token_.end()}))
+    CHECK(StringRefContainsPointer(token_, pos))
         << "invalid diagnostic location";
     llvm::StringRef prefix = token_.take_front(pos - token_.begin());
     auto [before_last_newline, this_line] = prefix.rsplit('\n');
diff --git a/toolchain/lexer/tokenized_buffer.cpp b/toolchain/lexer/tokenized_buffer.cpp
index e0ad9946429d..38af659bc270 100644
--- a/toolchain/lexer/tokenized_buffer.cpp
+++ b/toolchain/lexer/tokenized_buffer.cpp
@@ -11,6 +11,7 @@
 #include <string>
 
 #include "common/check.h"
+#include "common/string_helpers.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/StringSwitch.h"
@@ -901,8 +902,7 @@ auto TokenizedBuffer::TokenIterator::Print(llvm::raw_ostream& output) const
 
 auto TokenizedBuffer::SourceBufferLocationTranslator::GetLocation(
     const char* loc) -> Diagnostic::Location {
-  CHECK(llvm::is_sorted(std::array{buffer_->source_->Text().begin(), loc,
-                                   buffer_->source_->Text().end()}))
+  CHECK(StringRefContainsPointer(buffer_->source_->Text(), loc))
       << "location not within buffer";
   int64_t offset = loc - buffer_->source_->Text().begin();