Fix a bug in TreeCursor.matchContext

FIX: Fix a bug in `TreeCursor.matchContext` where, if the context fell
partially in a buffer node and partially in tree nodes, it could return
incorrect results.

Closes codemirror/dev#1449

src/tree.ts

@@ -815,7 +815,7 @@ abstract class BaseNode implements SyntaxNode {
   }
 
   matchContext(context: readonly string[]): boolean {
-    return matchNodeContext(this, context)
+    return matchNodeContext(this.parent, context)
   }
 
   enterUnfinishedNodesBefore(pos: number) {
@@ -935,8 +935,8 @@ function getChildren(node: SyntaxNode, type: string | number, before: string | n
   }
 }
 
-function matchNodeContext(node: SyntaxNode, context: readonly string[], i = context.length - 1): boolean {
-  for (let p: SyntaxNode | null = node.parent; i >= 0; p = p.parent) {
+function matchNodeContext(node: SyntaxNode | null, context: readonly string[], i = context.length - 1): boolean {
+  for (let p = node; i >= 0; p = p.parent) {
     if (!p) return false
     if (!p.type.isAnonymous) {
       if (context[i] && context[i] != p.name) return false
@@ -1331,10 +1331,10 @@ export class TreeCursor implements SyntaxNodeRef {
   /// of direct parent node names. Empty strings in the context array
   /// are treated as wildcards.
   matchContext(context: readonly string[]): boolean {
-    if (!this.buffer) return matchNodeContext(this.node, context)
+    if (!this.buffer) return matchNodeContext(this.node.parent, context)
     let {buffer} = this.buffer, {types} = buffer.set
     for (let i = context.length - 1, d = this.stack.length - 1; i >= 0; d--) {
-      if (d < 0) return matchNodeContext(this.node, context, i)
+      if (d < 0) return matchNodeContext(this._tree, context, i)
       let type = types[buffer.buffer[this.stack[d]]]
       if (!type.isAnonymous) {
         if (context[i] && context[i] != type.name) return false

test/test-tree.ts

@@ -324,3 +324,23 @@ describe("TreeCursor", () => {
     ist(c.type, NodeType.none)
   })
 })
+
+describe("matchContext", () => {
+  it("can match on nodes", () => {
+    ist(simple().resolve(10, 1).matchContext(["T", "Pa", "Br"]))
+  })
+
+  it("can match wildcards", () => {
+    ist(simple().resolve(10, 1).matchContext(["T", "", "Br"]))
+  })
+
+  it("can mismatch on nodes", () => {
+    ist(!simple().resolve(10, 1).matchContext(["Q", "Br"]))
+  })
+
+  it("can match on cursor", () => {
+    let c = simple().cursor()
+    for (let i = 0; i < 3; i++) c.enter(15, -1)
+    ist(c.matchContext(["T", "Pa", "Br"]))
+  })
+})