From b318e23f06322c0333418aaeda0fc65d709c8b97 Mon Sep 17 00:00:00 2001
From: Sebastian Sebbie Silbermann <sebastian.silbermann@vercel.com>
Date: Sun, 29 Mar 2026 13:44:08 -0700
Subject: [PATCH] Use trie for removeStringLiteralsMatchedByTemplateLiterals

Optimize removeStringLiteralsMatchedByTemplateLiterals by building a
prefix trie from TemplateLiteralType patterns and using O(L) trie
traversal per string literal instead of O(m) linear scan across all
templates. StringMappingType templates (which cannot be trie-indexed)
are checked separately.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
---
 internal/checker/checker.go | 52 +++++++++++++++++++++++++++----------
 internal/checker/relater.go | 47 +++++++++++++++++++++++++++++++++
 internal/checker/types.go   |  5 ++++
 3 files changed, 90 insertions(+), 14 deletions(-)

diff --git a/internal/checker/checker.go b/internal/checker/checker.go
index 79171ee859f..52a6bbb0d4c 100644
--- a/internal/checker/checker.go
+++ b/internal/checker/checker.go
@@ -25193,26 +25193,50 @@ func (c *Checker) removeRedundantLiteralTypes(types []*Type, includes TypeFlags,
 
 func (c *Checker) removeStringLiteralsMatchedByTemplateLiterals(types []*Type) []*Type {
 	templates := core.Filter(types, c.isPatternLiteralType)
-	if len(templates) != 0 {
-		i := len(types)
-		for i > 0 {
-			i--
-			t := types[i]
-			if t.flags&TypeFlagsStringLiteral != 0 && core.Some(templates, func(template *Type) bool {
-				return c.isTypeMatchedByTemplateLiteralOrStringMapping(t, template)
-			}) {
-				types = slices.Delete(types, i, i+1)
-			}
+	if len(templates) == 0 {
+		return types
+	}
+	templateLiterals := core.Filter(templates, func(t *Type) bool {
+		return t.flags&TypeFlagsTemplateLiteral != 0
+	})
+	stringMappings := core.Filter(templates, func(t *Type) bool {
+		return t.flags&TypeFlagsStringMapping != 0
+	})
+	var trie *templateLiteralTrieNode
+	if len(templateLiterals) >= 2 {
+		trie = c.buildTemplateLiteralTrieFromTypes(templateLiterals)
+	}
+	i := len(types)
+	for i > 0 {
+		i--
+		t := types[i]
+		if t.flags&TypeFlagsStringLiteral != 0 && c.isStringLiteralMatchedByTemplates(t, trie, templateLiterals, stringMappings) {
+			types = slices.Delete(types, i, i+1)
 		}
 	}
 	return types
 }
 
-func (c *Checker) isTypeMatchedByTemplateLiteralOrStringMapping(t *Type, template *Type) bool {
-	if template.flags&TypeFlagsTemplateLiteral != 0 {
-		return c.isTypeMatchedByTemplateLiteralType(t, template.AsTemplateLiteralType(), c.compareTypesAssignable)
+func (c *Checker) isStringLiteralMatchedByTemplates(source *Type, trie *templateLiteralTrieNode, templateLiterals []*Type, stringMappings []*Type) bool {
+	if trie != nil {
+		if c.findMatchingTemplateLiteralInTrie(trie, source, c.compareTypesAssignable) != nil {
+			return true
+		}
+	} else if len(templateLiterals) > 0 {
+		if core.Some(templateLiterals, func(tl *Type) bool {
+			return c.isTypeMatchedByTemplateLiteralType(source, tl.AsTemplateLiteralType(), c.compareTypesAssignable)
+		}) {
+			return true
+		}
 	}
-	return c.isMemberOfStringMapping(t, template)
+	if len(stringMappings) > 0 {
+		if core.Some(stringMappings, func(sm *Type) bool {
+			return c.isMemberOfStringMapping(source, sm)
+		}) {
+			return true
+		}
+	}
+	return false
 }
 
 func (c *Checker) removeConstrainedTypeVariables(types []*Type) []*Type {
diff --git a/internal/checker/relater.go b/internal/checker/relater.go
index 691bb1d24a0..b04681ae279 100644
--- a/internal/checker/relater.go
+++ b/internal/checker/relater.go
@@ -1105,6 +1105,53 @@ func (c *Checker) getMatchingUnionConstituentForType(unionType *Type, t *Type) *
 	return c.getConstituentTypeForKeyType(unionType, propType)
 }
 
+func (c *Checker) buildTemplateLiteralTrieFromTypes(templateTypes []*Type) *templateLiteralTrieNode {
+	root := &templateLiteralTrieNode{}
+	for _, t := range templateTypes {
+		prefix := t.AsTemplateLiteralType().texts[0]
+		node := root
+		for _, ch := range []byte(prefix) {
+			if node.children == nil {
+				node.children = make(map[byte]*templateLiteralTrieNode)
+			}
+			child := node.children[ch]
+			if child == nil {
+				child = &templateLiteralTrieNode{}
+				node.children[ch] = child
+			}
+			node = child
+		}
+		node.types = append(node.types, t)
+	}
+	return root
+}
+
+func (c *Checker) findMatchingTemplateLiteralInTrie(trie *templateLiteralTrieNode, source *Type, compareTypes TypeComparer) *Type {
+	value := source.AsLiteralType().Value().(string)
+	node := trie
+	// Check root candidates (empty-prefix templates like `${string}`)
+	for _, t := range node.types {
+		if c.isTypeMatchedByTemplateLiteralType(source, t.AsTemplateLiteralType(), compareTypes) {
+			return t
+		}
+	}
+	for _, ch := range []byte(value) {
+		if node.children == nil {
+			return nil
+		}
+		node = node.children[ch]
+		if node == nil {
+			return nil
+		}
+		for _, t := range node.types {
+			if c.isTypeMatchedByTemplateLiteralType(source, t.AsTemplateLiteralType(), compareTypes) {
+				return t
+			}
+		}
+	}
+	return nil
+}
+
 // Return the name of a discriminant property for which it was possible and feasible to construct a map of
 // constituent types keyed by the literal types of the property by that name in each constituent type. Return
 // an empty string if no such discriminant property exists.
diff --git a/internal/checker/types.go b/internal/checker/types.go
index 84e2e3fb093..4f9bba3b237 100644
--- a/internal/checker/types.go
+++ b/internal/checker/types.go
@@ -1059,6 +1059,11 @@ type TemplateLiteralType struct {
 func (t *TemplateLiteralType) Texts() []string { return t.texts }
 func (t *TemplateLiteralType) Types() []*Type  { return t.types }
 
+type templateLiteralTrieNode struct {
+	children map[byte]*templateLiteralTrieNode
+	types    []*Type // template literal types whose prefix ends at this node
+}
+
 type StringMappingType struct {
 	ConstrainedType
 	target *Type