[NFC] Add explicit deduction guides for CTAD (#6094)

Class template argument deduction (CTAD) is a C++17 feature that allows
variables to be declared with class template types without specifying the
template parameters. Deduction guides are a mechanism by which template authors
can control how the template parameters are inferred when CTAD is used. The
Google style guide prohibits the use of CTAD except where template authors opt
in to supporting it by providing explicit deduction guides. For compatibility
with users adhering to Google style, set the compiler flag to check this
condition and add the necessary deduction guides to make the compiler happy
again.

8 files changed, 30 insertions, 0 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 2aefeef05..4727100de 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -280,6 +280,11 @@ else()
   add_compile_flag("-Wimplicit-fallthrough")
   add_compile_flag("-Wnon-virtual-dtor")
 
+  if(CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
+    # Google style requires this, so make sure we compile cleanly with it.
+    add_compile_flag("-Wctad-maybe-unsupported")
+  endif()
+
   if(WIN32)
     add_compile_flag("-D_GNU_SOURCE")
     add_compile_flag("-D__STDC_FORMAT_MACROS")
diff --git a/src/analysis/lattices/inverted.h b/src/analysis/lattices/inverted.h
index 22e326742..b70e58968 100644
--- a/src/analysis/lattices/inverted.h
+++ b/src/analysis/lattices/inverted.h
@@ -49,6 +49,9 @@ template<FullLattice L> struct Inverted {
   }
 };
 
+// Deduction guide.
+template<typename L> Inverted(L&&) -> Inverted<L>;
+
 #if __cplusplus >= 202002L
 static_assert(Lattice<Inverted<Bool>>);
 #endif
diff --git a/src/analysis/lattices/lift.h b/src/analysis/lattices/lift.h
index ba711ac65..ec0f57967 100644
--- a/src/analysis/lattices/lift.h
+++ b/src/analysis/lattices/lift.h
@@ -74,6 +74,9 @@ template<Lattice L> struct Lift {
   }
 };
 
+// Deduction guide.
+template<typename L> Lift(L&&) -> Lift<L>;
+
 #if __cplusplus >= 202002L
 static_assert(Lattice<Lift<Bool>>);
 #endif
diff --git a/src/analysis/lattices/shared.h b/src/analysis/lattices/shared.h
index e75b895ea..54acf92b4 100644
--- a/src/analysis/lattices/shared.h
+++ b/src/analysis/lattices/shared.h
@@ -118,6 +118,9 @@ template<Lattice L> struct Shared {
   }
 };
 
+// Deduction guide.
+template<typename L> Shared(L&&) -> Shared<L>;
+
 #if __cplusplus >= 202002L
 static_assert(Lattice<Shared<Bool>>);
 #endif // __cplusplus >= 202002L
diff --git a/src/analysis/lattices/stack.h b/src/analysis/lattices/stack.h
index ad71cb1ac..c27965116 100644
--- a/src/analysis/lattices/stack.h
+++ b/src/analysis/lattices/stack.h
@@ -179,6 +179,9 @@ template<Lattice L> struct Stack {
   }
 };
 
+// Deduction guide.
+template<typename L> Stack(L&&) -> Stack<L>;
+
 #if __cplusplus >= 202002L
 static_assert(Lattice<Stack<Bool>>);
 #endif
diff --git a/src/analysis/lattices/vector.h b/src/analysis/lattices/vector.h
index 175ec5e3c..050b0f408 100644
--- a/src/analysis/lattices/vector.h
+++ b/src/analysis/lattices/vector.h
@@ -151,6 +151,9 @@ private:
   }
 };
 
+// Deduction guide.
+template<typename L> Vector(L&&, size_t) -> Vector<L>;
+
 #if __cplusplus >= 202002L
 static_assert(FullLattice<Vector<Bool>>);
 static_assert(Lattice<Vector<Flat<bool>>>);
diff --git a/src/analysis/monotone-analyzer.h b/src/analysis/monotone-analyzer.h
index 5ca8caacc..c2ec7c2b4 100644
--- a/src/analysis/monotone-analyzer.h
+++ b/src/analysis/monotone-analyzer.h
@@ -55,6 +55,10 @@ public:
   void print(std::ostream& os);
 };
 
+// Deduction guide.
+template<typename L, typename TxFn>
+MonotoneCFGAnalyzer(L&, TxFn&, CFG&) -> MonotoneCFGAnalyzer<L, TxFn>;
+
 } // namespace wasm::analysis
 
 #include "monotone-analyzer-impl.h"
diff --git a/src/wasm-type-printing.h b/src/wasm-type-printing.h
index c7277e96d..11afde882 100644
--- a/src/wasm-type-printing.h
+++ b/src/wasm-type-printing.h
@@ -95,6 +95,9 @@ struct IndexedTypeNameGenerator
   }
 };
 
+// Deduction guide.
+template<typename T> IndexedTypeNameGenerator(T&) -> IndexedTypeNameGenerator<>;
+
 // Prints heap types stored in a module, falling back to the given
 // FallbackGenerator if the module does not have a name for type type.
 template<typename FallbackGenerator = DefaultTypeNameGenerator>
@@ -122,6 +125,9 @@ struct ModuleTypeNameGenerator
   }
 };
 
+// Deduction guide.
+ModuleTypeNameGenerator(const Module&) -> ModuleTypeNameGenerator<>;
+
 } // namespace wasm
 
 #endif // wasm_wasm_type_printing_h