[llvm-go] parameterize $GOPATH construction

[axw]

Summary

To build llgo, you must currently ensure that llgo
is in the tools/llgo directory, due to a hard-coded
path in llvm-go.

To support the use of LLVM_EXTERNAL_LLGO_SOURCE_DIR,
we introduce a flag to llvm-go that enables the
caller to specify the paths to symlink in the
temporary $GOPATH.

[axw]

@pcc ping?

[pcc]

LGTM

cmake/modules/AddLLVM.cmake

if(LLVM_BINDINGS MATCHES "go")
     set(cxx "${CMAKE_CXX_COMPILER} ${CMAKE_CXX_COMPILER_ARG1}")
     set(cppflags "")
     get_property(include_dirs DIRECTORY PROPERTY INCLUDE_DIRECTORIES)
     foreach(d ${include_dirs})
       set(cppflags "${cppflags} -I${d}")
     endforeach(d)
     set(ldflags "${CMAKE_EXE_LINKER_FLAGS}")
     add_custom_command(OUTPUT ${binpath}
-      COMMAND ${CMAKE_BINARY_DIR}/bin/llvm-go "go=${GO_EXECUTABLE}" "cc=${cc}" "cxx=${cxx}" "cppflags=${cppflags}" "ldflags=${ldflags}"
+      COMMAND ${CMAKE_BINARY_DIR}/bin/llvm-go "go=${GO_EXECUTABLE}" "cc=${cc}" "cxx=${cxx}" "cppflags=${cppflags}" "ldflags=${ldflags}" "packages=${LLVM_GO_PACKAGES}"
               ${ARG_GOFLAGS} build -o ${binpath} ${pkgpath}
       DEPENDS llvm-config ${CMAKE_BINARY_DIR}/bin/llvm-go${CMAKE_EXECUTABLE_SUFFIX}
               ${llvmlibs} ${ARG_DEPENDS}
       COMMENT "Building Go executable ${binary}"
       VERBATIM)
     if (ARG_ALL)
       add_custom_target(${binary} ALL DEPENDS ${binpath})
     else()

tools/llvm-go/llvm-go.go

 )
 
 type pkg struct {
   llvmpath, pkgpath string
 }
 
 var packages = []pkg{
   {"bindings/go/llvm", "llvm.org/llvm/bindings/go/llvm"},
-  {"tools/llgo", "llvm.org/llgo"},
 }
 
 type compilerFlags struct {
   cpp, cxx, ld string
 }
 
 var components = []string{
   "all-targets",

 #cgo LDFLAGS: %s
 */
 import "C"
 
 type (run_build_sh int)
 `, flags.cpp, flags.cxx, flags.ld)
 }
 
-func runGoWithLLVMEnv(args []string, cc, cxx, gocmd, llgo, cppflags, cxxflags, ldflags string) {
+func runGoWithLLVMEnv(args []string, cc, cxx, gocmd, llgo, cppflags, cxxflags, ldflags string, packages []pkg) {
   args = addTag(args, "byollvm")
 
   srcdir := llvmConfig("--src-root")
 
   tmpgopath, err := ioutil.TempDir("", "gopath")
   if err != nil {
     panic(err.Error())
   }
 
   for _, p := range packages {
     path := filepath.Join(tmpgopath, "src", p.pkgpath)
     err := os.MkdirAll(filepath.Dir(path), os.ModePerm)
     if err != nil {
       panic(err.Error())
     }
 
-    err = os.Symlink(filepath.Join(srcdir, p.llvmpath), path)
+    abspath := p.llvmpath
+    if !filepath.IsAbs(abspath) {
+      abspath = filepath.Join(srcdir, abspath)
+    }
+
+    err = os.Symlink(abspath, path)
     if err != nil {
       panic(err.Error())
     }
   }
 
   newpath := os.Getenv("PATH")
 
   newgopathlist := []string{tmpgopath}

 func main() {
   cc := os.Getenv("CC")
   cxx := os.Getenv("CXX")
   cppflags := os.Getenv("CGO_CPPFLAGS")
   cxxflags := os.Getenv("CGO_CXXFLAGS")
   ldflags := os.Getenv("CGO_LDFLAGS")
   gocmd := "go"
   llgo := ""
+  packagesString := ""
 
   flags := []struct {
     name string
     dest *string
   }{
     {"cc", &cc},
     {"cxx", &cxx},
     {"go", &gocmd},
     {"llgo", &llgo},
     {"cppflags", &cppflags},
     {"ldflags", &ldflags},
+    {"packages", &packagesString},
   }
 
   args := os.Args[1:]
 LOOP:
   for {
     if len(args) == 0 {
       usage()
     }
     for _, flag := range flags {
       if strings.HasPrefix(args[0], flag.name+"=") {
         *flag.dest = args[0][len(flag.name)+1:]
         args = args[1:]
         continue LOOP
       }
     }
     break
   }
 
+  packages := packages
+  if packagesString != "" {
+    for _, field := range strings.Fields(packagesString) {
+      pos := strings.IndexRune(field, '=')
+      if pos == -1 {
+        fmt.Fprintf(os.Stderr, "invalid packages value %q, expected 'pkgpath=llvmpath [pkgpath=llvmpath ...]'\n", packagesString)
+        os.Exit(1)
+      }
+      packages = append(packages, pkg{
+        pkgpath:  field[:pos],
+        llvmpath: field[pos+1:],
+      })
+    }
+  }
+
   switch args[0] {
   case "build", "get", "install", "run", "test":
-    runGoWithLLVMEnv(args, cc, cxx, gocmd, llgo, cppflags, cxxflags, ldflags)
+    runGoWithLLVMEnv(args, cc, cxx, gocmd, llgo, cppflags, cxxflags, ldflags, packages)
   case "print-components":
     printComponents()
   case "print-config":
     printConfig()
   default:
     usage()
   }
 }