internal/parser: prevent infinite loop in value parsing

This should do some backtracking later, but let's fix the loop for now.

Author: stephen

esbuildplugin/plugin.go

@@ -1,6 +1,9 @@
 package esbuildplugin
 
 import (
+	"context"
+	"runtime/pprof"
+
 	"github.com/evanw/esbuild/pkg/api"
 	"github.com/samsarahq/go/oops"
 	"github.com/stephen/cssc"
@@ -86,6 +89,7 @@ func Plugin(opts ...Option) api.Plugin {
 						options = opt(options)
 					}
 
+					pprof.SetGoroutineLabels(pprof.WithLabels(context.TODO(), pprof.Labels("cssc-path", args.Path)))
 					result := cssc.Compile(options)
 
 					if len(errors) > 0 {

internal/parser/parser.go

@@ -408,7 +408,13 @@ func (p *parser) parseValue() ast.Value {
 					fn.Arguments = append(fn.Arguments, p.parseMathExpression())
 					continue
 				}
-				fn.Arguments = append(fn.Arguments, p.parseValue())
+				val := p.parseValue()
+				if val == nil {
+					// XXX: there's probably some backtracking to do here?
+					break arguments
+				}
+
+				fn.Arguments = append(fn.Arguments, val)
 			}
 		}