Language server refactoring

While there's more to do here, we've got to start somewhere.

- Simplify handlers by extracting shared logic
- Use "global" vars for static slices to avoid needless allocations
- No named return values
- Add GetContentAndModule convenience function to reduce boilerplate
- Various fixes

This should not change behavior of anything, just nake server.go
a little more manageable.

Signed-off-by: Anders Eknert <[email protected]>

internal/lsp/cache/cache.go

@@ -106,6 +106,20 @@ func (c *Cache) SetModule(fileURI string, module *ast.Module) {
 	c.modules.Set(fileURI, module)
 }
 
+func (c *Cache) GetContentAndModule(fileURI string) (string, *ast.Module, bool) {
+	content, ok := c.GetFileContents(fileURI)
+	if !ok {
+		return "", nil, false
+	}
+
+	module, ok := c.GetModule(fileURI)
+	if !ok {
+		return "", nil, false
+	}
+
+	return content, module, true
+}
+
 func (c *Cache) Rename(oldKey, newKey string) {
 	if content, ok := c.fileContents.Get(oldKey); ok {
 		c.fileContents.Set(newKey, content)

internal/lsp/handler/handler.go

@@ -0,0 +1,44 @@
+package handler
+
+import (
+	"context"
+
+	"github.com/anderseknert/roast/pkg/encoding"
+	"github.com/sourcegraph/jsonrpc2"
+)
+
+type handlerFunc[T any] func(T) (any, error)
+
+type handlerContextFunc[T any] func(context.Context, T) (any, error)
+
+var ErrInvalidParams = &jsonrpc2.Error{Code: jsonrpc2.CodeInvalidParams}
+
+func Decode[T any](req *jsonrpc2.Request, params *T) error {
+	if req.Params == nil {
+		return ErrInvalidParams
+	}
+
+	if err := encoding.JSON().Unmarshal(*req.Params, &params); err != nil {
+		return &jsonrpc2.Error{Code: jsonrpc2.CodeInvalidParams, Message: err.Error()}
+	}
+
+	return nil
+}
+
+func WithParams[T any](req *jsonrpc2.Request, h handlerFunc[T]) (any, error) {
+	var params T
+	if err := Decode(req, &params); err != nil {
+		return nil, err
+	}
+
+	return h(params)
+}
+
+func WithContextAndParams[T any](ctx context.Context, req *jsonrpc2.Request, h handlerContextFunc[T]) (any, error) {
+	var params T
+	if err := Decode(req, &params); err != nil {
+		return nil, err
+	}
+
+	return h(ctx, params)
+}