gopls version: v0.7.0
gopls flags: -rpc.trace serve --debug=localhost:6066
update flags: proxy
extension version: 0.26.0
go version: 1.16.6
environment: Visual Studio Code darwin
initialization error: undefined
manual restart count: 0
total start count: 1

Describe what you observed.

Opened runtime/malloc.go, which contained merge conflict markers. The relevant bit of code:

	// logHeapArenaBytes is log_2 of heapArenaBytes. For clarity,
	// prefer using heapArenaBytes where possible (we need the
	// constant to compute some other constants).
<<<<<<< HEAD
	logHeapArenaBytes = (6+20)*(_64bit*(1-sys.GoosWindows)*(1-sys.GoarchWasm)*(1-sys.GoosIos*sys.GoarchArm64)) + (2+20)*(_64bit*sys.GoosWindows) + (2+20)*(1-_64bit) + (2+20)*sys.GoarchWasm + (2+20)*sys.GoosIos*sys.GoarchArm64
||||||| parent of fad3ef219d ([tailscale1.16] runtime: add "runtime_small_arena" build tag to force 4MB heap arenas)
	logHeapArenaBytes = (6+20)*(_64bit*(1-sys.GoosWindows)*(1-sys.GoarchWasm)) + (2+20)*(_64bit*sys.GoosWindows) + (2+20)*(1-_64bit) + (2+20)*sys.GoarchWasm
=======
	logHeapArenaBytes = (6+20)*(_64bit*(1-sys.GoosWindows)*(1-sys.GoarchWasm)*(1-want4MB)) + (2+20)*(_64bit*sys.GoosWindows*(1-want4MB)) + (2+20)*(1-_64bit) + (2+20)*sys.GoarchWasm*(1-want4MB) + (2+20)*want4MB
>>>>>>> fad3ef219d ([tailscale1.16] runtime: add "runtime_small_arena" build tag to force 4MB heap arenas)

panic: assertion failed

goroutine 231 [running]:
go/types.(*Checker).handleBailout(0x14000017200, 0x14001f0f648)
	  check.go:245  0xa8
panic(0x100e4d1e0, 0x100f8f238)
	  panic.go:965  0x14c
go/types.assert(...)
	  errors.go:20
go/types.(*Checker).shift(0x14000017200, 0x1400226c500, 0x1400226c580, 0x14000c259b0, 0x14)
	  expr.go:709  0x99c
go/types.(*Checker).binary(0x14000017200, 0x1400226c500, 0x14000c259b0, 0x100fb2420, 0x14000648260, 0x100fb27e0, 0x14000648280, 0x14, 0x45a6d)
	  expr.go:821  0x108
go/types.(*Checker).exprInternal(0x14000017200, 0x1400226c500, 0x100fb2450, 0x14000c259b0, 0x0, 0x0, 0x0)
	  expr.go:1553  0x178c
go/types.(*Checker).rawExpr(0x14000017200, 0x1400226c500, 0x100fb2450, 0x14000c259b0, 0x0, 0x0, 0x40)
	  expr.go:1029  0x50
go/types.(*Checker).multiExpr(0x14000017200, 0x1400226c500, 0x100fb2450, 0x14000c259b0)
	  expr.go:1652  0x44
go/types.(*Checker).expr(0x14000017200, 0x1400226c500, 0x100fb2450, 0x14000c259b0)
	  expr.go:1646  0x40
go/types.(*Checker).binary(0x14000017200, 0x1400226c500, 0x14000c25a10, 0x100fb2450, 0x14000c259b0, 0x100fb27e0, 0x140006482a0, 0x2c, 0x45a81)
	  expr.go:808  0x60
go/types.(*Checker).exprInternal(0x14000017200, 0x1400226c500, 0x100fb2450, 0x14000c25a10, 0x0, 0x0, 0x100e9cdc0)
	  expr.go:1553  0x178c
go/types.(*Checker).rawExpr(0x14000017200, 0x1400226c500, 0x100fb2450, 0x14000c25a10, 0x0, 0x0, 0x40)
	  expr.go:1029  0x50
go/types.(*Checker).multiExpr(0x14000017200, 0x1400226c500, 0x100fb2450, 0x14000c25a10)
	  expr.go:1652  0x44
go/types.(*Checker).expr(0x14000017200, 0x1400226c500, 0x100fb2450, 0x14000c25a10)
	  expr.go:1646  0x40
go/types.(*Checker).stmt(0x14000017200, 0x0, 0x100fb26c0, 0x14000628280)
	  stmt.go:735  0x191c
go/types.(*Checker).stmtList(0x14000017200, 0x0, 0x14000a74690, 0x1, 0x1)
	  stmt.go:120  0xc4
go/types.(*Checker).stmt(0x14000017200, 0x0, 0x100fb2480, 0x14000c25bc0)
	  stmt.go:495  0x3a9c
go/types.(*Checker).stmt(0x14000017200, 0x0, 0x100fb2810, 0x140006282c0)
	  stmt.go:507  0x3d34
go/types.(*Checker).stmtList(0x14000017200, 0x0, 0x14000a29000, 0x13, 0x20)
	  stmt.go:120  0xc4
go/types.(*Checker).funcBody(0x14000017200, 0x14000fd4d80, 0x140006071d0, 0xa, 0x14001090690, 0x14000c5a030, 0x0, 0x0)
	  stmt.go:42  0x168
go/types.(*Checker).funcDecl.func1()
	  decl.go:749  0x5c
go/types.(*Checker).processDelayed(0x14000017200, 0x0)
	  check.go:291  0x3c
go/types.(*Checker).checkFiles(0x14000017200, 0x14001619c00, 0x77, 0x80, 0x0, 0x0)
	  check.go:267  0xb4
go/types.(*Checker).Files(...)
	  check.go:250
golang.org/x/tools/internal/lsp/cache.doTypeCheck(0x100fb43f8, 0x140003e8a80, 0x140001c07e0, 0x140003dc0e0, 0x2, 0x14000476e70, 0x0, 0x0, 0x0, 0x0)
	  check.go:531  0xa30
golang.org/x/tools/internal/lsp/cache.typeCheck(0x100fb43f8, 0x140003e8a80, 0x140001c07e0, 0x140003dc0e0, 0x2, 0x14000476e70, 0x140007ca600, 0x0, 0x0)
	  check.go:309  0x6c
golang.org/x/tools/internal/lsp/cache.(*snapshot).buildPackageHandle.func1(0x100fb43f8, 0x140003e8a80, 0x100fa1998, 0x140001c07e0, 0x140001703c0, 0x100fb4a88)
	  check.go:120  0x158
golang.org/x/tools/internal/memoize.(*Handle).run.func1(0x14000390320, 0x100fb43f8, 0x140003e8a80, 0x14000279340, 0x100fa1998, 0x140001c07e0, 0x140007cb320)
	  memoize.go:322  0x84
created by golang.org/x/tools/internal/memoize.(*Handle).run
	  memoize.go:315  0x138
[Error - 2:16:13 PM]