[clang-tools-extra] [clangd] [C++20] [Modules] Introduce initial support for C++20 Modules (PR #66462)

[kadir çetinkaya via cfe-commits]

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@@ -0,0 +1,115 @@
+//===----------------- ModulesBuilder.h --------------------------*- C++-*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// Experimental support for C++20 Modules.
+//
+// Currently we simplify the implementations by preventing reusing module files
+// across different versions and different source files. But this is clearly a
+// waste of time and space in the end of the day.
+//
+// TODO: Supporting reusing module files across different versions and
+// different source files.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANGD_MODULES_BUILDER_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANGD_MODULES_BUILDER_H
+
+#include "GlobalCompilationDatabase.h"
+#include "ProjectModules.h"
+
+#include "support/Path.h"
+#include "support/ThreadsafeFS.h"
+
+#include "clang/Frontend/CompilerInvocation.h"
+
+#include "llvm/ADT/SmallString.h"
+
+#include <memory>
+
+namespace clang {
+namespace clangd {
+
+/// Store all the needed module files information to parse a single
+/// source file. e.g.,
+///
+///   ```
+///   // a.cppm
+///   export module a;
+///
+///   // b.cppm
+///   export module b;
+///   import a;
+///
+///   // c.cppm
+///   export module c;
+///   import a;
+///   ```
+///
+/// For the source file `c.cppm`, an instance of the class will store
+/// the module files for `a.cppm` and `b.cppm`. But the module file for `c.cppm`
+/// won't be stored. Since it is not needed to parse `c.cppm`.
+///
+/// Users should only get PrerequisiteModules from
+/// `ModulesBuilder::buildPrerequisiteModulesFor(...)`.
+///
+/// Users can detect whether the PrerequisiteModules is still up to date by
+/// calling the `canReuse()` member function.
+///
+/// The users should call `adjustHeaderSearchOptions(...)` to update the
+/// compilation commands to select the built module files first. Before calling
+/// `adjustHeaderSearchOptions()`, users should call `canReuse()` first to check
+/// if all the stored module files are valid. In case they are not valid,
+/// users should call `ModulesBuilder::buildPrerequisiteModulesFor(...)` again
+/// to get the new PrerequisiteModules.
+class PrerequisiteModules {
+public:
+  /// Change commands to load the module files recorded in this
+  /// PrerequisiteModules first.
+  virtual void
+  adjustHeaderSearchOptions(HeaderSearchOptions &Options) const = 0;
+
+  /// Whether or not the built module files are up to date.
+  /// Note that this can only be used after building the module files.
+  virtual bool
+  canReuse(const CompilerInvocation &CI,
+           llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem>) const = 0;
+
+  /// Return true if the modile file specified by ModuleName is built.
+  /// Note that this interface will only check the existence of the module
+  /// file instead of checking the validness of the module file.
+  virtual bool isModuleUnitBuilt(llvm::StringRef ModuleName) const = 0;
----------------
kadircet wrote:

i think we can drop this from the interface. it's only used by tests or modulebuilder internals.

internally we already build modules with concrete standalone-prereq-modules, hence we can just expose the method there. for tests we should use the public `adjustHeaderSearchOptions` to check if a module-name is part of the set or not.

https://github.com/llvm/llvm-project/pull/66462