compiler: add support for type parameters (aka generics)

...that was surprisingly easy.

loader/loader.go

@@ -28,6 +28,8 @@ import (
 	"github.com/tinygo-org/tinygo/goenv"
 )
 
+var addInstances func(*types.Info)
+
 // Program holds all packages and some metadata about the program as a whole.
 type Program struct {
 	config       *compileopts.Config
@@ -164,6 +166,9 @@ func Load(config *compileopts.Config, inputPkg string, clangHeaders string, type
 				Selections: make(map[*ast.SelectorExpr]*types.Selection),
 			},
 		}
+		if addInstances != nil {
+			addInstances(&pkg.info)
+		}
 		err := decoder.Decode(&pkg.PackageJSON)
 		if err != nil {
 			if err == io.EOF {

loader/loader_go118.go

@@ -0,0 +1,18 @@
+//go:build go1.18
+// +build go1.18
+
+package loader
+
+// Workaround for Go 1.17 support. Should be removed once we drop Go 1.17
+// support.
+
+import (
+	"go/ast"
+	"go/types"
+)
+
+func init() {
+	addInstances = func(info *types.Info) {
+		info.Instances = make(map[*ast.Ident]types.Instance)
+	}
+}

loader/ssa.go

@@ -8,7 +8,7 @@ import (
 //
 // The program must already be parsed and type-checked with the .Parse() method.
 func (p *Program) LoadSSA() *ssa.Program {
-	prog := ssa.NewProgram(p.fset, ssa.SanityCheckFunctions|ssa.BareInits|ssa.GlobalDebug)
+	prog := ssa.NewProgram(p.fset, ssa.SanityCheckFunctions|ssa.BareInits|ssa.GlobalDebug|ssa.InstantiateGenerics)
 
 	for _, pkg := range p.sorted {
 		prog.CreatePackage(pkg.Pkg, pkg.Files, &pkg.info, true)