x/tools/gopls: type assertion panics in persistent.Map.Get

[adonovan]

#!stacks
"panicdottypeE" && "persistent.(*Map[...]).Get:=182"

Issue created by stacks.

// Get returns the map value associated with the specified key.
// The ok result indicates whether an entry was found in the map.
func (pm *Map[K, V]) Get(key K) (V, bool) {
	node := pm.root
	for node != nil {
		if key < node.key.(K) {           <--------- panic
			node = node.left
		} else if node.key.(K) < key {
			node = node.right
		} else {
			return node.value.value.(V), true
		}
	}
	var zero V
	return zero, false
}

This stack BPhXeQ was reported by telemetry:

• crash/crash
• runtime.gopanic:+69
• runtime.panicdottypeE:+1
• golang.org/x/tools/gopls/internal/util/persistent.(*Map[...]).Get:=182
• golang.org/x/tools/gopls/internal/cache.(*packageHandleBuilder).evaluatePackageHandle:+2
• golang.org/x/tools/gopls/internal/cache.(*Snapshot).getPackageHandles.func2.1:+8
• golang.org/x/sync/errgroup.(*Group).Go.func1:+3
• runtime.goexit:+0

golang.org/x/tools/gopls@v0.17.1 go1.23.4 linux/amd64 vscode (1)

[adonovan]

Every variable of type mapNode is constructed with a value for its key field, copied from either another mapNode (the inductive case) or from the k parameter of newNodeWithRef. Therefore this bug, in which its value is not of type k, "can't happen". Another sign of a data race?

[gabyhelp]

Related Issues

• x/tools/gopls: sigpanic in persistent.(*mapNode).forEach #71115
• x/tools/gopls: "nil handle" assert in getPackageHandles #71353
• x/tools/gopls: "expected exported symbol" assert in getOneTransitiveRefLocked #71356
• x/tools/gopls: "nil metadata for %q" panic in Snapshot.getPackageHandles (reported by telemetry) #66144 (closed)
• x/tools/gopls: OOB index crash in completion.expectedReturnStmtType #70636 (closed)
• x/tools/gopls: Hover: invalid nil entry in types.Defs map #69362 (closed)
• go/types: panic("t.fromRHS = %s, typ = %s") in setDefType #71029 (closed)
• x/tools/gopls: xrefs.Index panics after "can't fail" pgf.PosRange #70446 (closed)
• x/tools/gopls: panic in token.File.Name within PackageDocHTML (telemetry) #70149 (closed)
• x/tools/gopls: Rename: type assertion panics in renameImports #71656

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