compiler: Fix package dependency order calculation

The algorithm is now simpler and seems to work better.

tgo.go

@@ -124,7 +124,7 @@ func (c *Compiler) Parse(mainPath string, buildTags []string) error {
 
 	// TODO: pick the error of the first package, not a random package
 	for _, pkgInfo := range lprogram.AllPackages {
-		fmt.Println("package:", pkgInfo.Pkg.Name())
+		fmt.Println("package:", pkgInfo.Pkg.Path())
 		if len(pkgInfo.Errors) != 0 {
 			return pkgInfo.Errors[0]
 		}
@@ -136,23 +136,24 @@ func (c *Compiler) Parse(mainPath string, buildTags []string) error {
 	// Make a list of packages in import order.
 	packageList := []*ssa.Package{}
 	packageSet := map[string]struct{}{}
-	worklist := [][]string{{"runtime", mainPath}}
+	worklist := []string{"runtime", mainPath}
 	for len(worklist) != 0 {
-		for _, pkgPath := range worklist[0] {
+		pkgPath := worklist[0]
 		pkg := program.ImportedPackage(pkgPath)
 		if pkg == nil {
+			// Non-SSA package (e.g. cgo).
 			packageSet[pkgPath] = struct{}{}
-				continue // non-SSA package (e.g. cgo)
+			worklist = worklist[1:]
+			continue
 		}
 		if _, ok := packageSet[pkgPath]; ok {
+			// Package already in the final package list.
+			worklist = worklist[1:]
 			continue
 		}
 
 		unsatisfiedImports := make([]string, 0)
 		imports := pkg.Pkg.Imports()
-			if pkgPath != "runtime" && pkgPath != "unsafe" && pkgPath != "runtime/cgo" && pkgPath != "syscall" {
-				imports = append(imports, program.ImportedPackage("runtime").Pkg)
-			}
 		for _, pkg := range imports {
 			if _, ok := packageSet[pkg.Path()]; ok {
 				continue
@@ -160,15 +161,17 @@ func (c *Compiler) Parse(mainPath string, buildTags []string) error {
 			unsatisfiedImports = append(unsatisfiedImports, pkg.Path())
 		}
 		if len(unsatisfiedImports) == 0 {
-				// all dependencies are in packageList inserted
+			// All dependencies of this package are satisfied, so add this
+			// package to the list.
 			packageList = append(packageList, pkg)
 			packageSet[pkgPath] = struct{}{}
-			} else {
-				unsatisfiedImports = append(unsatisfiedImports, pkgPath) // reconsider
-				worklist = append(worklist, unsatisfiedImports)
-			}
-		}
 			worklist = worklist[1:]
+		} else {
+			// Prepend all dependencies to the worklist and reconsider this
+			// package (by not removing it from the worklist). At that point, it
+			// must be possible to add it to packageList.
+			worklist = append(unsatisfiedImports, worklist...)
+		}
 	}
 
 	// Transform each package into LLVM IR.
@@ -309,7 +312,7 @@ func (c *Compiler) getFunctionName(fn *ssa.Function) string {
 }
 
 func (c *Compiler) parsePackage(program *ssa.Program, pkg *ssa.Package) error {
-	fmt.Println("package:", pkg.Pkg.Path())
+	fmt.Println("\npackage:", pkg.Pkg.Path())
 
 	// Make sure we're walking through all members in a constant order every
 	// run.