desc, ok := m.descriptors[name]
	if !ok {
		panic(fmt.Sprintf("metric has no description: %s", name))
	}

	if len(labels)%2 != 0 {
		panic("labels must be a list of ordered key-value pairs")
	}

	validLabels := desc.getLabelSet()
	labelMap := make(map[string]string, len(labels)/2)
	for i := 0; i < len(labels); i += 2 {
		if _, ok := validLabels[labels[i]]; !ok {

func close(c chan<- Type)

// The panic built-in function stops normal execution of the current
// goroutine. When a function F calls panic, normal execution of F stops
// immediately. Any functions whose execution was deferred by F are run in
// the usual way, and then F returns to its caller. To the caller G, the
// invocation of F then behaves like a call to panic, terminating G's

// as we only guarantee a lookback buffer size of one, any subsequent calls to back()
// before calling next() may panic
func (s *scanner) back() {
	if s.ipos <= 0 {
		panic("back buffer exhausted")
	}
	s.ipos--
	s.pos--

The [GODEBUG History](#history) gives the exact defaults for each Go toolchain version.
For example, Go 1.21 introduces the `panicnil` setting,
controlling whether `panic(nil)` is allowed;
it defaults to `panicnil=0`, making `panic(nil)` a run-time error.
Using `panicnil=1` restores the behavior of Go 1.20 and earlier.

When compiling a work module or workspace that declares

		if debugPrint {
			fmt.Println("Mux", m.ID, "Handler took", time.Since(start).Round(time.Millisecond))
		}
		if r := recover(); r != nil {
			gridLogIf(ctx, fmt.Errorf("grid handler (%v) panic: %v", msg.Handler, r))
			err := RemoteErr(fmt.Sprintf("handler panic: %v", r))
			handlerErr = &err
		}
		if debugPrint {
			fmt.Println("muxServer: Mux", m.ID, "Returned with", handlerErr)
		}
	}()

	}
}

type panicReader struct{ panic bool }

func (r panicReader) Read(p []byte) (int, error) {
	if r.panic {
		panic("oops")
	}
	return 0, io.EOF
}

// Make sure that an empty Buffer remains empty when
// it is "grown" before a Read that panics
func TestReadFromPanicReader(t *testing.T) {

	// First verify non-panic behaviour
	var buf Buffer

At that point, the program is terminated and the error
condition is reported, including the value of the argument to <code>panic</code>.
This termination sequence is called <i>panicking</i>.
</p>

<pre>
panic(42)
panic("unreachable")
panic(Error("cannot parse"))
</pre>

<p>
The <code>recover</code> function allows a program to manage behavior
of a panicking goroutine.

func TestDontLoopForever(t *testing.T) {
	s := NewScanner(strings.NewReader("abc"))
	s.Split(loopAtEOFSplit)
	// Expect a panic
	defer func() {
		err := recover()
		if err == nil {
			t.Fatal("should have panicked")
		}
		if msg, ok := err.(string); !ok || !strings.Contains(msg, "empty tokens") {
			panic(err)
		}
	}()
	for count := 0; s.Scan(); count++ {
		if count > 1000 {
			t.Fatal("looping")
		}
	}

package main

import (
	"go/ast"
	"go/token"
)

func (f *File) walkUnexpected(x interface{}, context astContext, visit func(*File, interface{}, astContext)) {
	error_(token.NoPos, "unexpected type %T in walk", x)
	panic("unexpected type")
}

func funcTypeTypeParams(n *ast.FuncType) *ast.FieldList {
	return nil
}

func typeSpecTypeParams(n *ast.TypeSpec) *ast.FieldList {
	return nil

	if _, dup := decompressors.LoadOrStore(method, dcomp); dup {
		panic("decompressor already registered")
	}
}

// RegisterCompressor registers custom compressors for a specified method ID.
// The common methods [Store] and [Deflate] are built in.
func RegisterCompressor(method uint16, comp Compressor) {
	if _, dup := compressors.LoadOrStore(method, comp); dup {
		panic("compressor already registered")
	}
}