Use `absl::from_chars` instead of `strtod`

This CL switches Tint to use `absl::from_chars` instead of `strtod` in
order to have locale independent parsing of floats.

Bug: tint:1686
Change-Id: Icb3d9a40928a1cb154b32629f7e39173d80e4563
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/122780
Reviewed-by: David Neto <dneto@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Dan Sinclair <dsinclair@chromium.org>

src/tint/BUILD.gn

@@ -14,6 +14,7 @@
 
 import("//build_overrides/build.gni")
 
+import("../../scripts/dawn_overrides_with_defaults.gni")
 import("../../tint_overrides_with_defaults.gni")
 
 if (tint_build_unittests) {
@@ -92,6 +93,17 @@ config("tint_config") {
   }
 }
 
+group("abseil") {
+  # When build_with_chromium=true we need to include "//third_party/abseil-cpp:absl" while
+  # it's beneficial to be more specific with standalone Dawn, especially when it comes to
+  # including it as a dependency in other projects (such as Skia).
+  if (build_with_chromium) {
+    public_deps = [ "$dawn_abseil_dir:absl" ]
+  } else {
+    public_deps = [ "${dawn_root}/third_party/gn/abseil-cpp:strings" ]
+  }
+}
+
 ###############################################################################
 # Helper library for IO operations
 # Only to be used by tests and sample executable
@@ -953,6 +965,7 @@ libtint_source_set("libtint_wgsl_reader_src") {
   ]
 
   deps = [
+    ":abseil",
     ":libtint_ast_src",
     ":libtint_base_src",
     ":libtint_builtins_src",

src/tint/CMakeLists.txt

@@ -760,7 +760,7 @@ target_link_libraries(tint_val tint_utils_io)
 ## Tint library
 add_library(libtint ${TINT_LIB_SRCS})
 tint_default_compile_options(libtint)
-target_link_libraries(libtint tint_diagnostic_utils)
+target_link_libraries(libtint tint_diagnostic_utils absl_strings)
 if (${TINT_SYMBOL_STORE_DEBUG_NAME})
     target_compile_definitions(libtint PUBLIC "TINT_SYMBOL_STORE_DEBUG_NAME=1")
 endif()
@@ -770,7 +770,7 @@ if (${TINT_BUILD_FUZZERS})
   # Tint library with fuzzer instrumentation
   add_library(libtint-fuzz ${TINT_LIB_SRCS})
   tint_default_compile_options(libtint-fuzz)
-  target_link_libraries(libtint-fuzz tint_diagnostic_utils)
+  target_link_libraries(libtint-fuzz tint_diagnostic_utils absl_strings)
   if (${COMPILER_IS_LIKE_GNU})
     target_compile_options(libtint-fuzz PRIVATE -fvisibility=hidden)
   endif()

src/tint/reader/wgsl/lexer.cc

@@ -25,6 +25,7 @@
 #include <type_traits>
 #include <utility>
 
+#include "absl/strings/charconv.h"
 #include "src/tint/debug.h"
 #include "src/tint/number.h"
 #include "src/tint/text/unicode.h"
@@ -352,9 +353,11 @@ Token Lexer::try_float() {
 
     // Parse the exponent if one exists
     bool has_exponent = false;
+    bool negative_exponent = false;
     if (end < length() && (matches(end, 'e') || matches(end, 'E'))) {
         end++;
         if (end < length() && (matches(end, '+') || matches(end, '-'))) {
+            negative_exponent = matches(end, '-');
             end++;
         }
 
@@ -374,10 +377,8 @@ Token Lexer::try_float() {
     bool has_f_suffix = false;
     bool has_h_suffix = false;
     if (end < length() && matches(end, 'f')) {
-        end++;
         has_f_suffix = true;
     } else if (end < length() && matches(end, 'h')) {
-        end++;
         has_h_suffix = true;
     }
 
@@ -386,29 +387,51 @@ Token Lexer::try_float() {
         return {};
     }
 
-    advance(end - start);
-    end_source(source);
+    // Note, the `at` method will return a static `0` if the provided position is >= length. We
+    // actually need the end pointer to point to the correct memory location to use `from_chars`.
+    // So, handle the case where we point past the length specially.
+    auto* end_ptr = &at(end);
+    if (end >= length()) {
+        end_ptr = &at(length() - 1) + 1;
+    }
 
-    double value = std::strtod(&at(start), nullptr);
+    double value = 0;
+    auto ret = absl::from_chars(&at(start), end_ptr, value);
+    bool overflow = ret.ec != std::errc();
+
+    // The provided value did not fit in a double and has a negative exponent, so treat it as a 0.
+    if (negative_exponent && ret.ec == std::errc::result_out_of_range) {
+        overflow = false;
+        value = 0.0;
+    }
+
+    TINT_ASSERT(Reader, end_ptr == ret.ptr);
+    advance(end - start);
 
     if (has_f_suffix) {
-        if (auto f = CheckedConvert<f32>(AFloat(value))) {
+        auto f = CheckedConvert<f32>(AFloat(value));
+        if (!overflow && f) {
+            advance(1);
+            end_source(source);
             return {Token::Type::kFloatLiteral_F, source, static_cast<double>(f.Get())};
-        } else {
-            return {Token::Type::kError, source, "value cannot be represented as 'f32'"};
         }
+        return {Token::Type::kError, source, "value cannot be represented as 'f32'"};
     }
 
     if (has_h_suffix) {
-        if (auto f = CheckedConvert<f16>(AFloat(value))) {
+        auto f = CheckedConvert<f16>(AFloat(value));
+        if (!overflow && f) {
+            advance(1);
+            end_source(source);
             return {Token::Type::kFloatLiteral_H, source, static_cast<double>(f.Get())};
-        } else {
+        }
         return {Token::Type::kError, source, "value cannot be represented as 'f16'"};
     }
-    }
+
+    end_source(source);
 
     TINT_BEGIN_DISABLE_WARNING(FLOAT_EQUAL);
-    if (value == HUGE_VAL || -value == HUGE_VAL) {
+    if (overflow || value == HUGE_VAL || -value == HUGE_VAL) {
         return {Token::Type::kError, source, "value cannot be represented as 'abstract-float'"};
     } else {
         return {Token::Type::kFloatLiteral, source, value};

src/tint/reader/wgsl/lexer_test.cc

@@ -397,7 +397,7 @@ TEST_P(FloatTest, Parse) {
     Lexer l(&file);
 
     auto list = l.Lex();
-    ASSERT_EQ(2u, list.size());
+    ASSERT_EQ(2u, list.size()) << "Got: " << list[0].to_str();
 
     {
         auto& t = list[0];