[build] Enable -Wctad-maybe-unsupported

Enable a clang warning that embedders might enable, and fix issues
found by it.

R=ahaas@chromium.org, nicohartmann@chromium.org, mlippautz@chromium.org

Bug: v8:13069
Change-Id: I935f18872178f4421b441f33ef8ab1d8f030dfc6
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3760443
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Nico Hartmann <nicohartmann@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81853}

BUILD.gn

@@ -1318,6 +1318,11 @@ config("toolchain") {
     cflags += [
       "-Wmissing-field-initializers",
 
+      # Google3 enables this warning, so we should also enable it to find issue
+      # earlier. See https://reviews.llvm.org/D56731 for details about this
+      # warning.
+      "-Wctad-maybe-unsupported",
+
       # TODO(v8:12245): Fix shadowing instances and remove.
       "-Wno-shadow",
     ]

src/base/small-vector.h

@@ -100,11 +100,11 @@ class SmallVector {
   T* end() { return end_; }
   const T* end() const { return end_; }
 
-  auto rbegin() { return std::reverse_iterator{end_}; }
+  auto rbegin() { return std::make_reverse_iterator(end_); }
-  auto rbegin() const { return std::reverse_iterator{end_}; }
+  auto rbegin() const { return std::make_reverse_iterator(end_); }
 
-  auto rend() { return std::reverse_iterator{begin_}; }
+  auto rend() { return std::make_reverse_iterator(begin_); }
-  auto rend() const { return std::reverse_iterator{begin_}; }
+  auto rend() const { return std::make_reverse_iterator(begin_); }
 
   size_t size() const { return end_ - begin_; }
   bool empty() const { return end_ == begin_; }

src/base/string-format.h

@@ -171,6 +171,11 @@ class FormattedString {
   std::tuple<Part<Ts>...> parts_;
 };
 
+// Add an explicit deduction guide for empty template parameters (fixes
+// clang's -Wctad-maybe-unsupported warning). Non-empty formatted strings
+// explicitly declare template parameters anyway.
+FormattedString()->FormattedString<>;
+
 }  // namespace v8::base
 
 #endif  // V8_BASE_STRING_FORMAT_H_

src/compiler/turboshaft/graph.h

@@ -551,9 +551,9 @@ class Graph {
   }
 
   base::iterator_range<base::DerefPtrIterator<Block>> blocks() {
-    return {
+    return {base::DerefPtrIterator<Block>(bound_blocks_.data()),
-        base::DerefPtrIterator(bound_blocks_.data()),
+            base::DerefPtrIterator<Block>(bound_blocks_.data() +
-        base::DerefPtrIterator(bound_blocks_.data() + bound_blocks_.size())};
+                                          bound_blocks_.size())};
   }
   base::iterator_range<base::DerefPtrIterator<const Block>> blocks() const {
     return {base::DerefPtrIterator<const Block>(bound_blocks_.data()),

src/heap/cppgc/write-barrier.cc

@@ -215,7 +215,7 @@ YoungGenerationEnabler& YoungGenerationEnabler::Instance() {
 
 void YoungGenerationEnabler::Enable() {
   auto& instance = Instance();
-  v8::base::LockGuard _(&instance.mutex_);
+  v8::base::MutexGuard _(&instance.mutex_);
   if (++instance.is_enabled_ == 1) {
     // Enter the flag so that the check in the write barrier will always trigger
     // when young generation is enabled.
@@ -225,7 +225,7 @@ void YoungGenerationEnabler::Enable() {
 
 void YoungGenerationEnabler::Disable() {
   auto& instance = Instance();
-  v8::base::LockGuard _(&instance.mutex_);
+  v8::base::MutexGuard _(&instance.mutex_);
   DCHECK_LT(0, instance.is_enabled_);
   if (--instance.is_enabled_ == 0) {
     WriteBarrier::FlagUpdater::Exit();
@@ -234,7 +234,7 @@ void YoungGenerationEnabler::Disable() {
 
 bool YoungGenerationEnabler::IsEnabled() {
   auto& instance = Instance();
-  v8::base::LockGuard _(&instance.mutex_);
+  v8::base::MutexGuard _(&instance.mutex_);
   return instance.is_enabled_;
 }
 

src/utils/bit-vector.h

@@ -282,7 +282,7 @@ class V8_EXPORT_PRIVATE BitVector : public ZoneObject {
       return data_.inline_ == 0;
     } else {
       return std::all_of(data_.ptr_, data_.ptr_ + data_length_,
-                         std::logical_not{});
+                         std::logical_not<uintptr_t>{});
     }
   }
 

src/wasm/module-decoder-impl.h

@@ -297,6 +297,10 @@ class WasmSectionIterator {
   }
 };
 
+// Add an explicit template deduction guide for {WasmSectionIterator}.
+template <class T>
+WasmSectionIterator(Decoder*, T) -> WasmSectionIterator<T>;
+
 // The main logic for decoding the bytes of a module.
 template <class Tracer>
 class ModuleDecoderTemplate : public Decoder {