Make `llvm-config` detect whether or not LLVM is a shared library. If it is, then only try to link …

tools/llvm-config/llvm-config.cpp

 //===-- llvm-config.cpp - LLVM project configuration utility --------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This tool encapsulates information about an LLVM project configuration for
@@ skipping 331 matching lines @@
     // If no components were specified, default to "all".
     if (Components.empty())
       Components.push_back("all");
 
     // Construct the list of all the required libraries.
     std::vector<StringRef> RequiredLibs;
     ComputeLibsForComponents(Components, RequiredLibs,
                              /*IncludeNonInstalled=*/IsInDevelopmentTree);
 
     if (PrintLibs || PrintLibNames || PrintLibFiles) {
+      // If LLVM was built as a shared library, there will be only one thing
+      // that users should link against.
+      const bool IsSharedLib = (std::strcmp(BUILD_SHARED_LIBS, "ON") == 0);
+      const bool WasBuiltWithCMake = (std::strcmp(WAS_BUILT_WITH_CMAKE, "ON") == 0);
+      // CMake correctly builds components as separate shared libraries, however
+      // autoconfig/make builds components a static libraries and then links
+      // them all together to form a single shared library. Thus, only when
+      // `WAS_BUILT_WITH_CMAKE` and `BUILD_SHARED_LIBS` are `ON` do we override
+      // `RequiredLibs` with the single library name.
+      if (IsSharedLib && !WasBuiltWithCMake) {
+        RequiredLibs.clear();
+        std::string Name = "libLLVM-" PACKAGE_VERSION;
+        const Triple HostTriple(LLVM_DEFAULT_TARGET_TRIPLE);
+        if (HostTriple.isOSWindows()) {
+          Name += ".dll";
+        } else if (HostTriple.isOSDarwin()) {
+          Name += ".dylib";
+        } else {
+          // default to linux' ext:
+          Name += ".so";
+        }
+        RequiredLibs.push_back(Name);
+      }
+
       for (unsigned i = 0, e = RequiredLibs.size(); i != e; ++i) {
         StringRef Lib = RequiredLibs[i];
         if (i)
           OS << ' ';
 
         if (PrintLibNames) {
           OS << Lib;
         } else if (PrintLibFiles) {
           OS << ActiveLibDir << '/' << Lib;
         } else if (PrintLibs) {
           // If this is a typical library name, include it using -l.
-          if (Lib.startswith("lib") && Lib.endswith(".a")) {
-            OS << "-l" << Lib.slice(3, Lib.size()-2);
-            continue;
+          if (Lib.startswith("lib")) {
+            size_t FromEnd = 0;
+            do {
+              if (Lib.endswith(".a")) {
+                FromEnd = 2;
+              } else if (Lib.endswith(".so")) {
+                FromEnd = 3;
+              } else if (Lib.endswith(".dylib")) {
+                FromEnd = 6;
+              } else {
+                FromEnd = 0;
+                break;
+              }
+              OS << "-l" << Lib.slice(3, Lib.size() - FromEnd);
+            } while(false);
+            if (FromEnd != 0) { continue; }
           }
 
           // Otherwise, print the full path.
           OS << ActiveLibDir << '/' << Lib;
         }
       }
       OS << '\n';
     }
 
     // Print SYSTEM_LIBS after --libs.
     // FIXME: Each LLVM component may have its dependent system libs.
     if (PrintSystemLibs)
       OS << LLVM_SYSTEM_LIBS << '\n';
   } else if (!Components.empty()) {
     errs() << "llvm-config: error: components given, but unused\n\n";
     usage();
   }
 
   return 0;
 }