compiler: add support for type parameters (aka generics)

...that was surprisingly easy.

compiler/compiler.go

@@ -21,6 +21,10 @@ import (
 	"tinygo.org/x/go-llvm"
 )
 
+var typeParamUnderlyingType = func(t types.Type) types.Type {
+	return t
+}
+
 func init() {
 	llvm.InitializeAllTargets()
 	llvm.InitializeAllTargetMCs()
@@ -335,6 +339,7 @@ func (c *compilerContext) getLLVMType(goType types.Type) llvm.Type {
 // makeLLVMType creates a LLVM type for a Go type. Don't call this, use
 // getLLVMType instead.
 func (c *compilerContext) makeLLVMType(goType types.Type) llvm.Type {
+	goType = typeParamUnderlyingType(goType)
 	switch typ := goType.(type) {
 	case *types.Array:
 		elemType := c.getLLVMType(typ.Elem())
@@ -444,6 +449,7 @@ func (c *compilerContext) getDIType(typ types.Type) llvm.Metadata {
 // createDIType creates a new DWARF type. Don't call this function directly,
 // call getDIType instead.
 func (c *compilerContext) createDIType(typ types.Type) llvm.Metadata {
+	typ = typeParamUnderlyingType(typ)
 	llvmType := c.getLLVMType(typ)
 	sizeInBytes := c.targetData.TypeAllocSize(llvmType)
 	switch typ := typ.(type) {
@@ -794,6 +800,9 @@ func (c *compilerContext) createPackage(irbuilder llvm.Builder, pkg *ssa.Package
 			for _, method := range methods {
 				// Parse this method.
 				fn := pkg.Prog.MethodValue(method)
+				if fn == nil {
+					continue // probably a generic method
+				}
 				if fn.Blocks == nil {
 					continue // external function
 				}

compiler/compiler_go118.go

@@ -0,0 +1,18 @@
+//go:build go1.18
+// +build go1.18
+
+package compiler
+
+// Workaround for Go 1.17 support. Should be removed once we drop Go 1.17
+// support.
+
+import "go/types"
+
+func init() {
+	typeParamUnderlyingType = func(t types.Type) types.Type {
+		if t, ok := t.(*types.TypeParam); ok {
+			return t.Underlying()
+		}
+		return t
+	}
+}

compiler/symbol.go

@@ -191,7 +191,7 @@ func (c *compilerContext) getFunction(fn *ssa.Function) llvm.Value {
 	// should be created right away.
 	// The exception is the package initializer, which does appear in the
 	// *ssa.Package members and so shouldn't be created here.
-	if fn.Synthetic != "" && fn.Synthetic != "package initializer" {
+	if fn.Synthetic != "" && fn.Synthetic != "package initializer" && fn.Synthetic != "generic function" {
 		irbuilder := c.ctx.NewBuilder()
 		b := newBuilder(c, irbuilder, fn)
 		b.createFunction()