[clangd] Allow using customized include path in URI.

Summary:
Calculating the include path from absolute file path does not always
work for all build system, e.g. bazel uses symlink as the build working
directory. The absolute file path from editor and clang is diverged from
each other. We need to address it properly in build sysmtem integration.

This patch worksarounds the issue by providing a hook in URI which allows
clients to provide their customized include path.

Reviewers: sammccall

Subscribers: klimek, ilya-biryukov, jkorous-apple, ioeric, MaskRay, cfe-commits

Differential Revision: https://reviews.llvm.org/D45426

llvm-svn: 329578

clang-tools-extra/clangd/ClangdServer.cpp

@@ -286,6 +286,13 @@ static llvm::Expected<HeaderFile> toHeaderFile(StringRef Header,
   auto U = URI::parse(Header);
   if (!U)
     return U.takeError();
+
+  auto IncludePath = URI::includeSpelling(*U);
+  if (!IncludePath)
+    return IncludePath.takeError();
+  if (!IncludePath->empty())
+    return HeaderFile{std::move(*IncludePath), /*Verbatim=*/true};
+
   auto Resolved = URI::resolve(*U, HintPath);
   if (!Resolved)
     return Resolved.takeError();

clang-tools-extra/clangd/URI.cpp

@@ -196,5 +196,12 @@ llvm::Expected<std::string> URI::resolve(const URI &Uri,
   return S->get()->getAbsolutePath(Uri.Authority, Uri.Body, HintPath);
 }
 
+llvm::Expected<std::string> URI::includeSpelling(const URI &Uri) {
+  auto S = findSchemeByName(Uri.Scheme);
+  if (!S)
+    return S.takeError();
+  return S->get()->getIncludeSpelling(Uri);
+}
+
 } // namespace clangd
 } // namespace clang

clang-tools-extra/clangd/URI.h

@@ -60,6 +60,16 @@ public:
   static llvm::Expected<std::string> resolve(const URI &U,
                                              llvm::StringRef HintPath = "");
 
+  /// Gets the preferred spelling of this file for #include, if there is one,
+  /// e.g. <system_header.h>, "path/to/x.h".
+  ///
+  /// This allows URI schemas to provide their customized include paths.
+  ///
+  /// Returns an empty string if normal include-shortening based on the absolute
+  /// path should be used.
+  /// Fails if the URI is not valid in the schema.
+  static llvm::Expected<std::string> includeSpelling(const URI &U);
+
   friend bool operator==(const URI &LHS, const URI &RHS) {
     return std::tie(LHS.Scheme, LHS.Authority, LHS.Body) ==
            std::tie(RHS.Scheme, RHS.Authority, RHS.Body);
@@ -94,6 +104,13 @@ public:
 
   virtual llvm::Expected<URI>
   uriFromAbsolutePath(llvm::StringRef AbsolutePath) const = 0;
+
+  /// Returns the include path of the file (e.g. <path>, "path"), which can be
+  /// #included directly. See URI::includeSpelling for details.
+  virtual llvm::Expected<std::string>
+  getIncludeSpelling(const URI& U) const {
+    return "";  // no customized include path for this scheme.
+  }
 };
 
 /// By default, a "file" scheme is supported where URI paths are always absolute

clang-tools-extra/unittests/clangd/ClangdTests.cpp

@@ -152,6 +152,28 @@ protected:
   }
 };
 
+constexpr const char* ClangdTestScheme = "ClangdTests";
+class TestURIScheme : public URIScheme {
+public:
+  llvm::Expected<std::string>
+  getAbsolutePath(llvm::StringRef /*Authority*/, llvm::StringRef Body,
+                  llvm::StringRef /*HintPath*/) const override {
+    llvm_unreachable("ClangdTests never makes absolute path.");
+  }
+
+  llvm::Expected<URI>
+  uriFromAbsolutePath(llvm::StringRef AbsolutePath) const override {
+    llvm_unreachable("ClangdTest never creates a test URI.");
+  }
+
+  llvm::Expected<std::string> getIncludeSpelling(const URI &U) const override {
+    return ("\"" + U.body().trim("/") + "\"").str();
+  }
+};
+
+static URISchemeRegistry::Add<TestURIScheme>
+    X(ClangdTestScheme, "Test scheme for ClangdTests.");
+
 TEST_F(ClangdVFSTest, Parse) {
   // FIXME: figure out a stable format for AST dumps, so that we can check the
   // output of the dump itself is equal to the expected one, not just that it's
@@ -961,6 +983,10 @@ void f() {}
                        /*Preferred=*/"<Y.h>", "<Y.h>"));
   EXPECT_TRUE(Inserted(OriginalHeader, PreferredHeader, "\"Y.h\""));
   EXPECT_TRUE(Inserted("<y.h>", PreferredHeader, "\"Y.h\""));
+  auto TestURIHeader =
+      URI::parse(llvm::formatv("{0}:///x/y/z.h", ClangdTestScheme).str());
+  EXPECT_TRUE(static_cast<bool>(TestURIHeader));
+  EXPECT_TRUE(Inserted(TestURIHeader->toString(), "", "\"x/y/z.h\""));
 
   // Check that includes are sorted.
   const auto Expected = R"cpp(