AST: Refactor missing import diagnostic into standalone utility.

NFC.

Author: tshortli

include/swift/AST/Decl.h

@@ -2788,7 +2788,7 @@ class ValueDecl : public Decl {
 public:
   /// Find the import that makes the given declaration available.
   std::optional<AttributedImport<ImportedModule>>
-  findImport(const DeclContext *fromDC);
+  findImport(const DeclContext *fromDC) const;
 
   /// Return true if this protocol member is a protocol requirement.
   ///

include/swift/AST/DiagnosticsSema.def

@@ -167,9 +167,9 @@ ERROR(init_candidate_inaccessible,none,
 
 ERROR(candidate_from_missing_import,none,
       "%0 %1 is not available due to missing import of defining module %2",
-      (DescriptiveDeclKind, DeclName, DeclName))
+      (DescriptiveDeclKind, DeclName, ModuleDecl *))
 NOTE(candidate_add_import,none,
-     "add import of module %0", (DeclName))
+     "add import of module %0", (ModuleDecl *))
 
 ERROR(cannot_pass_rvalue_mutating_subelement,none,
       "cannot use mutating member on immutable value: %0",

include/swift/AST/Module.h

@@ -1269,6 +1269,11 @@ void collectParsedExportedImports(const ModuleDecl *M,
                                   llvm::SmallDenseMap<ModuleDecl *, SmallPtrSet<Decl *, 4>, 4> &QualifiedImports,
                                   llvm::function_ref<bool(AttributedImport<ImportedModule>)> includeImport = nullptr);
 
+/// If the import that would make the given declaration visibile is absent,
+/// emit a diagnostic and a fix-it suggesting adding the missing import.
+bool diagnoseMissingImportForMember(const ValueDecl *decl,
+                                    const DeclContext *dc, SourceLoc loc);
+
 } // end namespace swift
 
 #endif

lib/AST/Decl.cpp

@@ -3865,7 +3865,7 @@ ValueDecl::getSatisfiedProtocolRequirements(bool Sorted) const {
 }
 
 std::optional<AttributedImport<ImportedModule>>
-ValueDecl::findImport(const DeclContext *fromDC) {
+ValueDecl::findImport(const DeclContext *fromDC) const {
   // If the type is from the current module, there's no import.
   auto module = getModuleContext();
   if (module == fromDC->getParentModule())

lib/AST/Module.cpp

@@ -4001,3 +4001,40 @@ version::Version ModuleDecl::getLanguageVersionBuiltWith() const {
 
   return version::Version();
 }
+
+bool swift::diagnoseMissingImportForMember(const ValueDecl *decl,
+                                           const DeclContext *dc,
+                                           SourceLoc loc) {
+  if (decl->findImport(dc))
+    return false;
+
+  auto &ctx = dc->getASTContext();
+  auto definingModule = decl->getModuleContext();
+  ctx.Diags.diagnose(loc, diag::candidate_from_missing_import,
+                     decl->getDescriptiveKind(), decl->getName(),
+                     definingModule);
+
+  SourceLoc bestLoc =
+      ctx.Diags.getBestAddImportFixItLoc(decl, dc->getParentSourceFile());
+  if (bestLoc.isValid()) {
+    llvm::SmallString<64> importText;
+
+    // @_spi imports.
+    if (decl->isSPI()) {
+      auto spiGroups = decl->getSPIGroups();
+      if (!spiGroups.empty()) {
+        importText += "@_spi(";
+        importText += spiGroups[0].str();
+        importText += ") ";
+      }
+    }
+
+    importText += "import ";
+    importText += definingModule->getName().str();
+    importText += "\n";
+    ctx.Diags.diagnose(bestLoc, diag::candidate_add_import, definingModule)
+        .fixItInsert(bestLoc, importText);
+  }
+
+  return true;
+}

lib/Sema/CSDiagnostics.cpp

@@ -6187,39 +6187,11 @@ bool InaccessibleMemberFailure::diagnoseAsError() {
 
   auto loc = nameLoc.isValid() ? nameLoc.getStartLoc() : ::getLoc(anchor);
   auto accessLevel = Member->getFormalAccessScope().accessLevelForDiagnostics();
-  bool suppressDeclHereNote = false;
   if (accessLevel == AccessLevel::Public &&
-      !Member->findImport(getDC())) {
-    auto definingModule = Member->getDeclContext()->getParentModule();
-    emitDiagnosticAt(loc, diag::candidate_from_missing_import,
-                     Member->getDescriptiveKind(), Member->getName(),
-                     definingModule->getName());
-
-    SourceLoc bestLoc =
-        getBestAddImportFixItLocation(Member, getDC()->getParentSourceFile());
-    if (bestLoc.isValid()) {
-      llvm::SmallString<64> importText;
-
-      // @_spi imports.
-      if (Member->isSPI()) {
-        auto spiGroups = Member->getSPIGroups();
-        if (!spiGroups.empty()) {
-          importText += "@_spi(";
-          importText += spiGroups[0].str();
-          importText += ") ";
-        }
-      }
-
-      importText += "import ";
-      importText += definingModule->getName().str();
-      importText += "\n";
-      emitDiagnosticAt(bestLoc, diag::candidate_add_import,
-                       definingModule->getName())
-        .fixItInsert(bestLoc, importText);
-    }
+      diagnoseMissingImportForMember(Member, getDC(), loc))
+    return true;
 
-    suppressDeclHereNote = true;
-  } else if (auto *CD = dyn_cast<ConstructorDecl>(Member)) {
+  if (auto *CD = dyn_cast<ConstructorDecl>(Member)) {
     emitDiagnosticAt(loc, diag::init_candidate_inaccessible,
                      CD->getResultInterfaceType(), accessLevel)
         .highlight(nameLoc.getSourceRange());
@@ -6229,8 +6201,7 @@ bool InaccessibleMemberFailure::diagnoseAsError() {
         .highlight(nameLoc.getSourceRange());
   }
 
-  if (!suppressDeclHereNote)
-    emitDiagnosticAt(Member, diag::decl_declared_here, Member);
+  emitDiagnosticAt(Member, diag::decl_declared_here, Member);
   return true;
 }