Add -Wmissing-prototypes and fix issues it finds.

Most of these are places where we failed to include a header file and
simply never got an error about this. The fix is to include the header
file.

Most other cases are functions that should have been marked `static` but
were not. Finding all of these was a main motivation for me enabling the
warning despite how much work it is.

One complicating factor was that we weren't including the `handle.h` for
all the state-based handler functions. While this isn't a tiny amount of
code, it is just declarations and doesn't add any extra dependencies. It
also lets us have the checking for which functions need to be `static`
and which don't. For the `parse` library I had to add the `handle.h`
header as well, I tried to match the design of it in `check`.

I have also had to work around a bug in the warning, but given the value
it seems to be providing, that seems reasonable. I've filed the bug
upstream: bazelbuild/bazel#22610

I also had to use some hacks to work around limitations of Bazel rules
that wrap `cc_library` rules and don't expose `copts`. I filed a bug for
`cc_proto_library` specifically:
bazelbuild/bazel#22610

.bazelrc

@@ -28,6 +28,21 @@ build --experimental_guard_against_concurrent_changes
 build --per_file_copt=external/.*\.(c|cc|cpp|cxx)$@-w
 build --host_per_file_copt=external/.*\.(c|cc|cpp|cxx)$@-w
 
+# The `rules_treesitter` synthesized libraries don't allow us to inject flags,
+# and compile generated code where we can't fix warnings.
+build --per_file_copt=utils/treesitter/_treesitter.tree_sitter/.*\.c$@-w
+build --host_per_file_copt=utils/treesitter/_treesitter.tree_sitter/.*\.c$@-w
+
+# The `cc_proto_library` rule doesn't allow providing `copts`:
+# https://github.com/bazelbuild/bazel/issues/22610
+#
+# We unfortunately need to work around issues with `-Wmissing-prototypes` in
+# generated protobuf code, so pass the `copt` manually here. The warning issue
+# is likely part of:
+# https://github.com/llvm/llvm-project/issues/94138
+build --per_file_copt=.*\.pb\.cc$@-Wno-missing-prototypes
+build --host_per_file_copt=.*\.pb\.cc$@-Wno-missing-prototypes
+
 # Default dynamic linking to off. While this can help build performance in some
 # edge cases with very large linked executables and a slow linker, between using
 # fast linkers on all platforms (LLD and the Apple linker), as well as having

bazel/cc_toolchains/clang_cc_toolchain_config.bzl

@@ -142,6 +142,7 @@ def _impl(ctx):
                             "-Wimplicit-fallthrough",
                             "-Wctad-maybe-unsupported",
                             "-Wextra-semi",
+                            "-Wmissing-prototypes",
                             "-Wzero-as-null-pointer-constant",
                             # Don't warn on external code as we can't
                             # necessarily patch it easily. Note that these have

common/check_internal.cpp

@@ -10,7 +10,7 @@
 namespace Carbon::Internal {
 
 // Prints the buffered message.
-auto PrintAfterStackTrace(void* str) -> void {
+static auto PrintAfterStackTrace(void* str) -> void {
   llvm::errs() << reinterpret_cast<char*>(str);
 }
 

explorer/ast/value.cpp

@@ -1042,7 +1042,7 @@ auto TypeEqual(Nonnull<const Value*> t1, Nonnull<const Value*> t2,
 
 // Returns true if the two values are known to be equal and are written in the
 // same way at the top level.
-auto ValueStructurallyEqual(
+static auto ValueStructurallyEqual(
     Nonnull<const Value*> v1, Nonnull<const Value*> v2,
     std::optional<Nonnull<const EqualityContext*>> equality_ctx) -> bool {
   if (v1 == v2) {

explorer/fuzzing/BUILD

@@ -110,6 +110,7 @@ cc_fuzz_test(
     name = "explorer_fuzzer",
     size = "small",
     srcs = ["explorer_fuzzer.cpp"],
+    copts = ["-Wno-missing-prototypes"],
     corpus = glob(["fuzzer_corpus/*"]),
     shard_count = 8,
     tags = [

explorer/fuzzing/ast_to_proto_main.cpp

@@ -21,7 +21,7 @@
 
 namespace Carbon::Testing {
 
-auto Main(int argc, char** argv) -> ErrorOr<Success> {
+static auto Main(int argc, char** argv) -> ErrorOr<Success> {
   SetWorkingDirForBazel();
 
   if (argc != 2) {

explorer/interpreter/resolve_control_flow.cpp

@@ -170,8 +170,9 @@ static auto ResolveControlFlow(Nonnull<TraceStream*> trace_stream,
   }
 }
 
-auto ResolveControlFlow(Nonnull<TraceStream*> trace_stream,
-                        Nonnull<Declaration*> declaration) -> ErrorOr<Success> {
+static auto ResolveControlFlow(Nonnull<TraceStream*> trace_stream,
+                               Nonnull<Declaration*> declaration)
+    -> ErrorOr<Success> {
   switch (declaration->kind()) {
     case DeclarationKind::DestructorDeclaration:
     case DeclarationKind::FunctionDeclaration: {

testing/fuzzing/proto_to_carbon_main.cpp

@@ -17,7 +17,7 @@
 
 namespace Carbon {
 
-auto Main(int argc, char** argv) -> ErrorOr<Success> {
+static auto Main(int argc, char** argv) -> ErrorOr<Success> {
   Carbon::SetWorkingDirForBazel();
 
   if (argc != 2) {

toolchain/check/check_fuzzer.cpp

@@ -9,6 +9,12 @@
 
 namespace Carbon::Testing {
 
+// Declare this first to work around a bug in `-Wmissing-prototypes`:
+// https://github.com/llvm/llvm-project/issues/94138
+// NOLINTNEXTLINE: Match the documented fuzzer entry point declaration style.
+extern "C" int LLVMFuzzerTestOneInput(const unsigned char* data,
+                                      std::size_t size);
+
 // NOLINTNEXTLINE: Match the documented fuzzer entry point declaration style.
 extern "C" int LLVMFuzzerTestOneInput(const unsigned char* data,
                                       std::size_t size) {

toolchain/check/eval.cpp

@@ -317,8 +317,8 @@ static auto PerformAggregateIndex(Context& context, SemIR::Inst inst)
 }
 
 // Enforces that an integer type has a valid bit width.
-auto ValidateIntType(Context& context, SemIRLoc loc, SemIR::IntType result)
-    -> bool {
+static auto ValidateIntType(Context& context, SemIRLoc loc,
+                            SemIR::IntType result) -> bool {
   auto bit_width =
       context.insts().TryGetAs<SemIR::IntLiteral>(result.bit_width_id);
   if (!bit_width) {
@@ -381,8 +381,8 @@ static auto ValidateFloatBitWidth(Context& context, SemIRLoc loc,
 }
 
 // Enforces that a float type has a valid bit width.
-auto ValidateFloatType(Context& context, SemIRLoc loc, SemIR::FloatType result)
-    -> bool {
+static auto ValidateFloatType(Context& context, SemIRLoc loc,
+                              SemIR::FloatType result) -> bool {
   auto bit_width =
       context.insts().TryGetAs<SemIR::IntLiteral>(result.bit_width_id);
   if (!bit_width) {

toolchain/check/handle_alias.cpp

@@ -3,6 +3,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include "toolchain/check/context.h"
+#include "toolchain/check/handle.h"
 #include "toolchain/check/modifiers.h"
 #include "toolchain/check/name_component.h"
 #include "toolchain/parse/node_ids.h"

toolchain/check/handle_array.cpp

@@ -4,6 +4,7 @@
 
 #include "toolchain/check/context.h"
 #include "toolchain/check/convert.h"
+#include "toolchain/check/handle.h"
 #include "toolchain/parse/node_kind.h"
 
 namespace Carbon::Check {

toolchain/check/handle_binding_pattern.cpp

@@ -4,14 +4,15 @@
 
 #include "toolchain/check/context.h"
 #include "toolchain/check/convert.h"
+#include "toolchain/check/handle.h"
 #include "toolchain/check/return.h"
 #include "toolchain/sem_ir/ids.h"
 #include "toolchain/sem_ir/inst.h"
 
 namespace Carbon::Check {
 
-auto HandleAnyBindingPattern(Context& context, Parse::NodeId node_id,
-                             bool is_generic) -> bool {
+static auto HandleAnyBindingPattern(Context& context, Parse::NodeId node_id,
+                                    bool is_generic) -> bool {
   auto [type_node, parsed_type_id] = context.node_stack().PopExprWithNodeId();
   auto cast_type_id = ExprAsType(context, type_node, parsed_type_id);
 

toolchain/check/handle_call_expr.cpp

@@ -4,6 +4,7 @@
 
 #include "toolchain/check/call.h"
 #include "toolchain/check/context.h"
+#include "toolchain/check/handle.h"
 #include "toolchain/sem_ir/inst.h"
 
 namespace Carbon::Check {

toolchain/check/handle_choice.cpp

@@ -3,6 +3,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include "toolchain/check/context.h"
+#include "toolchain/check/handle.h"
 
 namespace Carbon::Check {
 

toolchain/check/handle_class.cpp

@@ -7,6 +7,7 @@
 #include "toolchain/check/convert.h"
 #include "toolchain/check/decl_name_stack.h"
 #include "toolchain/check/eval.h"
+#include "toolchain/check/handle.h"
 #include "toolchain/check/merge.h"
 #include "toolchain/check/modifiers.h"
 #include "toolchain/check/name_component.h"

toolchain/check/handle_codeblock.cpp

@@ -3,6 +3,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include "toolchain/check/context.h"
+#include "toolchain/check/handle.h"
 
 namespace Carbon::Check {
 

toolchain/check/handle_export.cpp

@@ -4,6 +4,7 @@
 
 #include "toolchain/check/context.h"
 #include "toolchain/check/decl_name_stack.h"
+#include "toolchain/check/handle.h"
 #include "toolchain/check/modifiers.h"
 #include "toolchain/check/name_component.h"
 #include "toolchain/parse/typed_nodes.h"

toolchain/check/handle_expr_statement.cpp

@@ -4,6 +4,7 @@
 
 #include "toolchain/check/context.h"
 #include "toolchain/check/convert.h"
+#include "toolchain/check/handle.h"
 #include "toolchain/sem_ir/inst.h"
 
 namespace Carbon::Check {

toolchain/check/handle_file.cpp

@@ -3,6 +3,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include "toolchain/check/context.h"
+#include "toolchain/check/handle.h"
 
 namespace Carbon::Check {
 

toolchain/check/handle_function.cpp

@@ -8,6 +8,7 @@
 #include "toolchain/check/decl_name_stack.h"
 #include "toolchain/check/decl_state.h"
 #include "toolchain/check/function.h"
+#include "toolchain/check/handle.h"
 #include "toolchain/check/interface.h"
 #include "toolchain/check/merge.h"
 #include "toolchain/check/modifiers.h"

toolchain/check/handle_if_expr.cpp

@@ -4,6 +4,7 @@
 
 #include "toolchain/check/context.h"
 #include "toolchain/check/convert.h"
+#include "toolchain/check/handle.h"
 
 namespace Carbon::Check {
 

toolchain/check/handle_if_statement.cpp

@@ -4,6 +4,7 @@
 
 #include "toolchain/check/context.h"
 #include "toolchain/check/convert.h"
+#include "toolchain/check/handle.h"
 
 namespace Carbon::Check {
 

toolchain/check/handle_impl.cpp

@@ -5,6 +5,7 @@
 #include "toolchain/check/context.h"
 #include "toolchain/check/convert.h"
 #include "toolchain/check/decl_name_stack.h"
+#include "toolchain/check/handle.h"
 #include "toolchain/check/impl.h"
 #include "toolchain/check/modifiers.h"
 #include "toolchain/parse/typed_nodes.h"

toolchain/check/handle_import_and_package.cpp

@@ -4,6 +4,7 @@
 
 #include "toolchain/check/context.h"
 #include "toolchain/check/decl_state.h"
+#include "toolchain/check/handle.h"
 #include "toolchain/check/modifiers.h"
 
 namespace Carbon::Check {

toolchain/check/handle_index.cpp

@@ -5,6 +5,7 @@
 #include "toolchain/base/kind_switch.h"
 #include "toolchain/check/context.h"
 #include "toolchain/check/convert.h"
+#include "toolchain/check/handle.h"
 #include "toolchain/sem_ir/inst.h"
 
 namespace Carbon::Check {

toolchain/check/handle_interface.cpp

@@ -3,6 +3,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include "toolchain/check/context.h"
+#include "toolchain/check/handle.h"
 #include "toolchain/check/interface.h"
 #include "toolchain/check/modifiers.h"
 #include "toolchain/check/name_component.h"

toolchain/check/handle_let.cpp

@@ -4,6 +4,7 @@
 
 #include "toolchain/check/context.h"
 #include "toolchain/check/convert.h"
+#include "toolchain/check/handle.h"
 #include "toolchain/check/interface.h"
 #include "toolchain/check/modifiers.h"
 #include "toolchain/diagnostics/diagnostic_emitter.h"

toolchain/check/handle_literal.cpp

@@ -4,6 +4,7 @@
 
 #include "toolchain/check/call.h"
 #include "toolchain/check/context.h"
+#include "toolchain/check/handle.h"
 #include "toolchain/sem_ir/typed_insts.h"
 
 namespace Carbon::Check {

toolchain/check/handle_loop_statement.cpp

@@ -4,6 +4,7 @@
 
 #include "toolchain/check/context.h"
 #include "toolchain/check/convert.h"
+#include "toolchain/check/handle.h"
 
 namespace Carbon::Check {
 

toolchain/check/handle_match.cpp

@@ -4,6 +4,7 @@
 
 #include "toolchain/check/context.h"
 #include "toolchain/check/convert.h"
+#include "toolchain/check/handle.h"
 
 namespace Carbon::Check {
 

toolchain/check/handle_modifier.cpp

@@ -4,6 +4,7 @@
 
 #include "toolchain/check/context.h"
 #include "toolchain/check/decl_state.h"
+#include "toolchain/check/handle.h"
 #include "toolchain/lex/token_kind.h"
 
 namespace Carbon::Check {

toolchain/check/handle_name.cpp

@@ -3,6 +3,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include "toolchain/check/context.h"
+#include "toolchain/check/handle.h"
 #include "toolchain/check/member_access.h"
 #include "toolchain/check/name_component.h"
 #include "toolchain/check/pointer_dereference.h"

toolchain/check/handle_named_constraint.cpp

@@ -3,6 +3,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include "toolchain/check/context.h"
+#include "toolchain/check/handle.h"
 
 namespace Carbon::Check {
 

toolchain/check/handle_namespace.cpp

@@ -4,6 +4,7 @@
 
 #include "toolchain/check/context.h"
 #include "toolchain/check/decl_state.h"
+#include "toolchain/check/handle.h"
 #include "toolchain/check/modifiers.h"
 #include "toolchain/check/name_component.h"
 #include "toolchain/sem_ir/ids.h"

toolchain/check/handle_noop.cpp

@@ -3,6 +3,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include "toolchain/check/context.h"
+#include "toolchain/check/handle.h"
 
 namespace Carbon::Check {
 

toolchain/check/handle_operator.cpp

@@ -4,6 +4,7 @@
 
 #include "toolchain/check/context.h"
 #include "toolchain/check/convert.h"
+#include "toolchain/check/handle.h"
 #include "toolchain/check/operator.h"
 #include "toolchain/check/pointer_dereference.h"
 #include "toolchain/diagnostics/diagnostic_emitter.h"

toolchain/check/handle_paren_expr.cpp

@@ -3,6 +3,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include "toolchain/check/context.h"
+#include "toolchain/check/handle.h"
 
 namespace Carbon::Check {
 

toolchain/check/handle_pattern_list.cpp

@@ -3,6 +3,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include "toolchain/check/context.h"
+#include "toolchain/check/handle.h"
 
 namespace Carbon::Check {
 

toolchain/check/handle_return_statement.cpp

@@ -3,6 +3,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include "toolchain/check/context.h"
+#include "toolchain/check/handle.h"
 #include "toolchain/check/return.h"
 
 namespace Carbon::Check {

toolchain/check/handle_struct.cpp

@@ -4,6 +4,7 @@
 
 #include "toolchain/check/context.h"
 #include "toolchain/check/convert.h"
+#include "toolchain/check/handle.h"
 
 namespace Carbon::Check {
 

toolchain/check/handle_tuple_literal.cpp

@@ -3,6 +3,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include "toolchain/check/context.h"
+#include "toolchain/check/handle.h"
 
 namespace Carbon::Check {
 

toolchain/check/handle_variable.cpp

@@ -4,6 +4,7 @@
 
 #include "toolchain/check/context.h"
 #include "toolchain/check/convert.h"
+#include "toolchain/check/handle.h"
 #include "toolchain/check/modifiers.h"
 
 namespace Carbon::Check {