perf(linker): Fixes brute force chunk cycle detection (#3069)

Author: ruiconti

internal/linker/linker.go

@@ -452,28 +452,41 @@ func (c *linkerContext) mangleProps(mangleCache map[string]interface{}) {
 // can cause initialization bugs. So let's forbid these cycles for now to guard
 // against code splitting bugs that could cause us to generate buggy chunks.
 func (c *linkerContext) enforceNoCyclicChunkImports() {
-	var validate func(int, []int)
-	validate = func(chunkIndex int, path []int) {
-		for _, otherChunkIndex := range path {
-			if chunkIndex == otherChunkIndex {
-				c.log.AddError(nil, logger.Range{}, "Internal error: generated chunks contain a circular import")
-				return
-			}
+	var validate func(int, map[int]int) bool
+
+	// DFS memoization with 3-colors, more space efficient
+	// 0: white (unvisited), 1: gray (visiting), 2: black (visited)
+	colors := make(map[int]int)
+	validate = func(chunkIndex int, colors map[int]int) bool {
+		if colors[chunkIndex] == 1 {
+			c.log.AddError(nil, logger.Range{}, "Internal error: generated chunks contain a circular import")
+			return true
 		}
-		path = append(path, chunkIndex)
+
+		if colors[chunkIndex] == 2 {
+			return false
+		}
+
+		colors[chunkIndex] = 1
+
 		for _, chunkImport := range c.chunks[chunkIndex].crossChunkImports {
-			// Ignore cycles caused by dynamic "import()" expressions. These are fine
-			// because they don't necessarily cause initialization order issues and
-			// they don't indicate a bug in our chunk generation algorithm. They arise
-			// normally in real code (e.g. two files that import each other).
 			if chunkImport.importKind != ast.ImportDynamic {
-				validate(int(chunkImport.chunkIndex), path)
+
+				// Recursively validate otherChunkIndex
+				if validate(int(chunkImport.chunkIndex), colors) {
+					return true
+				}
 			}
 		}
+
+		colors[chunkIndex] = 2
+		return false
 	}
-	path := make([]int, 0, len(c.chunks))
+
 	for i := range c.chunks {
-		validate(i, path)
+		if validate(i, colors) {
+			break
+		}
 	}
 }