[clang][NFC] Introduce SemaBase (#87634)

This is a follow-up to #84184. Multiple reviewers there pointed out to
me that we should have a common base class for `Sema` and `SemaOpenACC`
to avoid code duplication for common helpers like `getLangOpts()`. On
top of that, `Diag()` function was requested for `SemaOpenACC`. This
patch delivers both.

The intent is to keep `SemaBase` as small as possible, as things there
are globally available across `Sema` and its parts without any
additional effort from usage side. Overused, this can undermine the
whole endeavor of splitting `Sema` apart.

Apart of shuffling code around, this patch introduces a helper private
function `SemaDiagnosticBuilder::getDeviceDeferredDiags()`, the sole
purpose of which is to encapsulate member access into (incomplete)
`Sema` for function templates defined in the header, where `Sema` can't
be complete.

Author: Endilll

clang/include/clang/Sema/Sema.h

@@ -55,6 +55,7 @@
 #include "clang/Sema/ObjCMethodList.h"
 #include "clang/Sema/Ownership.h"
 #include "clang/Sema/Scope.h"
+#include "clang/Sema/SemaBase.h"
 #include "clang/Sema/SemaConcept.h"
 #include "clang/Sema/TypoCorrection.h"
 #include "clang/Sema/Weak.h"
@@ -422,7 +423,7 @@ enum class TemplateDeductionResult {
 
 /// Sema - This implements semantic analysis and AST building for C.
 /// \nosubgrouping
-class Sema final {
+class Sema final : public SemaBase {
   // Table of Contents
   // -----------------
   // 1. Semantic Analysis (Sema.cpp)
@@ -512,195 +513,6 @@ class Sema final {
   ///
   void addExternalSource(ExternalSemaSource *E);
 
-  /// Helper class that creates diagnostics with optional
-  /// template instantiation stacks.
-  ///
-  /// This class provides a wrapper around the basic DiagnosticBuilder
-  /// class that emits diagnostics. ImmediateDiagBuilder is
-  /// responsible for emitting the diagnostic (as DiagnosticBuilder
-  /// does) and, if the diagnostic comes from inside a template
-  /// instantiation, printing the template instantiation stack as
-  /// well.
-  class ImmediateDiagBuilder : public DiagnosticBuilder {
-    Sema &SemaRef;
-    unsigned DiagID;
-
-  public:
-    ImmediateDiagBuilder(DiagnosticBuilder &DB, Sema &SemaRef, unsigned DiagID)
-        : DiagnosticBuilder(DB), SemaRef(SemaRef), DiagID(DiagID) {}
-    ImmediateDiagBuilder(DiagnosticBuilder &&DB, Sema &SemaRef, unsigned DiagID)
-        : DiagnosticBuilder(DB), SemaRef(SemaRef), DiagID(DiagID) {}
-
-    // This is a cunning lie. DiagnosticBuilder actually performs move
-    // construction in its copy constructor (but due to varied uses, it's not
-    // possible to conveniently express this as actual move construction). So
-    // the default copy ctor here is fine, because the base class disables the
-    // source anyway, so the user-defined ~ImmediateDiagBuilder is a safe no-op
-    // in that case anwyay.
-    ImmediateDiagBuilder(const ImmediateDiagBuilder &) = default;
-
-    ~ImmediateDiagBuilder() {
-      // If we aren't active, there is nothing to do.
-      if (!isActive())
-        return;
-
-      // Otherwise, we need to emit the diagnostic. First clear the diagnostic
-      // builder itself so it won't emit the diagnostic in its own destructor.
-      //
-      // This seems wasteful, in that as written the DiagnosticBuilder dtor will
-      // do its own needless checks to see if the diagnostic needs to be
-      // emitted. However, because we take care to ensure that the builder
-      // objects never escape, a sufficiently smart compiler will be able to
-      // eliminate that code.
-      Clear();
-
-      // Dispatch to Sema to emit the diagnostic.
-      SemaRef.EmitCurrentDiagnostic(DiagID);
-    }
-
-    /// Teach operator<< to produce an object of the correct type.
-    template <typename T>
-    friend const ImmediateDiagBuilder &
-    operator<<(const ImmediateDiagBuilder &Diag, const T &Value) {
-      const DiagnosticBuilder &BaseDiag = Diag;
-      BaseDiag << Value;
-      return Diag;
-    }
-
-    // It is necessary to limit this to rvalue reference to avoid calling this
-    // function with a bitfield lvalue argument since non-const reference to
-    // bitfield is not allowed.
-    template <typename T,
-              typename = std::enable_if_t<!std::is_lvalue_reference<T>::value>>
-    const ImmediateDiagBuilder &operator<<(T &&V) const {
-      const DiagnosticBuilder &BaseDiag = *this;
-      BaseDiag << std::move(V);
-      return *this;
-    }
-  };
-
-  /// A generic diagnostic builder for errors which may or may not be deferred.
-  ///
-  /// In CUDA, there exist constructs (e.g. variable-length arrays, try/catch)
-  /// which are not allowed to appear inside __device__ functions and are
-  /// allowed to appear in __host__ __device__ functions only if the host+device
-  /// function is never codegen'ed.
-  ///
-  /// To handle this, we use the notion of "deferred diagnostics", where we
-  /// attach a diagnostic to a FunctionDecl that's emitted iff it's codegen'ed.
-  ///
-  /// This class lets you emit either a regular diagnostic, a deferred
-  /// diagnostic, or no diagnostic at all, according to an argument you pass to
-  /// its constructor, thus simplifying the process of creating these "maybe
-  /// deferred" diagnostics.
-  class SemaDiagnosticBuilder {
-  public:
-    enum Kind {
-      /// Emit no diagnostics.
-      K_Nop,
-      /// Emit the diagnostic immediately (i.e., behave like Sema::Diag()).
-      K_Immediate,
-      /// Emit the diagnostic immediately, and, if it's a warning or error, also
-      /// emit a call stack showing how this function can be reached by an a
-      /// priori known-emitted function.
-      K_ImmediateWithCallStack,
-      /// Create a deferred diagnostic, which is emitted only if the function
-      /// it's attached to is codegen'ed.  Also emit a call stack as with
-      /// K_ImmediateWithCallStack.
-      K_Deferred
-    };
-
-    SemaDiagnosticBuilder(Kind K, SourceLocation Loc, unsigned DiagID,
-                          const FunctionDecl *Fn, Sema &S);
-    SemaDiagnosticBuilder(SemaDiagnosticBuilder &&D);
-    SemaDiagnosticBuilder(const SemaDiagnosticBuilder &) = default;
-
-    // The copy and move assignment operator is defined as deleted pending
-    // further motivation.
-    SemaDiagnosticBuilder &operator=(const SemaDiagnosticBuilder &) = delete;
-    SemaDiagnosticBuilder &operator=(SemaDiagnosticBuilder &&) = delete;
-
-    ~SemaDiagnosticBuilder();
-
-    bool isImmediate() const { return ImmediateDiag.has_value(); }
-
-    /// Convertible to bool: True if we immediately emitted an error, false if
-    /// we didn't emit an error or we created a deferred error.
-    ///
-    /// Example usage:
-    ///
-    ///   if (SemaDiagnosticBuilder(...) << foo << bar)
-    ///     return ExprError();
-    ///
-    /// But see CUDADiagIfDeviceCode() and CUDADiagIfHostCode() -- you probably
-    /// want to use these instead of creating a SemaDiagnosticBuilder yourself.
-    operator bool() const { return isImmediate(); }
-
-    template <typename T>
-    friend const SemaDiagnosticBuilder &
-    operator<<(const SemaDiagnosticBuilder &Diag, const T &Value) {
-      if (Diag.ImmediateDiag)
-        *Diag.ImmediateDiag << Value;
-      else if (Diag.PartialDiagId)
-        Diag.S.DeviceDeferredDiags[Diag.Fn][*Diag.PartialDiagId].second
-            << Value;
-      return Diag;
-    }
-
-    // It is necessary to limit this to rvalue reference to avoid calling this
-    // function with a bitfield lvalue argument since non-const reference to
-    // bitfield is not allowed.
-    template <typename T,
-              typename = std::enable_if_t<!std::is_lvalue_reference<T>::value>>
-    const SemaDiagnosticBuilder &operator<<(T &&V) const {
-      if (ImmediateDiag)
-        *ImmediateDiag << std::move(V);
-      else if (PartialDiagId)
-        S.DeviceDeferredDiags[Fn][*PartialDiagId].second << std::move(V);
-      return *this;
-    }
-
-    friend const SemaDiagnosticBuilder &
-    operator<<(const SemaDiagnosticBuilder &Diag, const PartialDiagnostic &PD) {
-      if (Diag.ImmediateDiag)
-        PD.Emit(*Diag.ImmediateDiag);
-      else if (Diag.PartialDiagId)
-        Diag.S.DeviceDeferredDiags[Diag.Fn][*Diag.PartialDiagId].second = PD;
-      return Diag;
-    }
-
-    void AddFixItHint(const FixItHint &Hint) const {
-      if (ImmediateDiag)
-        ImmediateDiag->AddFixItHint(Hint);
-      else if (PartialDiagId)
-        S.DeviceDeferredDiags[Fn][*PartialDiagId].second.AddFixItHint(Hint);
-    }
-
-    friend ExprResult ExprError(const SemaDiagnosticBuilder &) {
-      return ExprError();
-    }
-    friend StmtResult StmtError(const SemaDiagnosticBuilder &) {
-      return StmtError();
-    }
-    operator ExprResult() const { return ExprError(); }
-    operator StmtResult() const { return StmtError(); }
-    operator TypeResult() const { return TypeError(); }
-    operator DeclResult() const { return DeclResult(true); }
-    operator MemInitResult() const { return MemInitResult(true); }
-
-  private:
-    Sema &S;
-    SourceLocation Loc;
-    unsigned DiagID;
-    const FunctionDecl *Fn;
-    bool ShowCallStack;
-
-    // Invariant: At most one of these Optionals has a value.
-    // FIXME: Switch these to a Variant once that exists.
-    std::optional<ImmediateDiagBuilder> ImmediateDiag;
-    std::optional<unsigned> PartialDiagId;
-  };
-
   void PrintStats() const;
 
   /// Warn that the stack is nearly exhausted.
@@ -742,14 +554,6 @@ class Sema final {
 
   void addImplicitTypedef(StringRef Name, QualType T);
 
-  /// Emit a diagnostic.
-  SemaDiagnosticBuilder Diag(SourceLocation Loc, unsigned DiagID,
-                             bool DeferHint = false);
-
-  /// Emit a partial diagnostic.
-  SemaDiagnosticBuilder Diag(SourceLocation Loc, const PartialDiagnostic &PD,
-                             bool DeferHint = false);
-
   /// Whether uncompilable error has occurred. This includes error happens
   /// in deferred diagnostics.
   bool hasUncompilableErrorOccurred() const;
@@ -13115,9 +12919,7 @@ class Sema final {
   /// Diagnostics that are emitted only if we discover that the given function
   /// must be codegen'ed.  Because handling these correctly adds overhead to
   /// compilation, this is currently only enabled for CUDA compilations.
-  llvm::DenseMap<CanonicalDeclPtr<const FunctionDecl>,
-                 std::vector<PartialDiagnosticAt>>
-      DeviceDeferredDiags;
+  SemaDiagnosticBuilder::DeferredDiagnosticsType DeviceDeferredDiags;
 
   /// A pair of a canonical FunctionDecl and a SourceLocation.  When used as the
   /// key in a hashtable, both the FD and location are hashed.