Fix NilAway FPs on channel sends/receives

[yuxincs]

See issue #192 for a more detailed discussion on handling channels in NilAway. To make this PR more self-contained, below is a partial copy of the discussion there:

See the following behaviors regarding nil / closed channels (taken from this SO post, slightly modified):

1. A send to a nil channel blocks forever
2. A receive from a nil channel blocks forever
3. A send to a closed channel panics
4. A receive from a closed channel returns the zero value immediately

Only case 3 (sending to a closed channel) will result in a panic. The other cases arguably may not be within scope of NilAway's analysis. Moreover, NilAway currently only tracks nilabilities of channels, but not the states of them, making it unable to really handle case 2 and 4.

Since this introduces a lot more FPs than TPs (if any), this PR removes logic to require sending to/receiving from nonnil channels. We leave properly handling channels as future work (especially around tracking states of channels).

The test cases have been updated to reflect this. Specifically, we kept the test cases there to now serve as negative cases in case for future development of such a support.

Fixes #98
Fixes #167

[github-actions]

Golden Test

Warning

❌ NilAway errors reported on stdlib are different 📉.

3043 errors on base branch (main, 9b1d75d)
3003 errors on test branch (6c337e8)

Diffs

- /opt/hostedtoolcache/go/1.21.6/x64/src/context/context_test.go:124:9: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- context/context.go:184:9: literal `nil` returned from `Done()` in position 0
- 	- context/context.go:105:2: returned as result 0 from interface method `Context.Done()` (implemented by `emptyCtx.Done()`)
- 	- context/context_test.go:124:9: result 0 of `Done()` uninitialized; nil channel accessed via the assignment(s):
- 		- `WithValue(...)` to `precanceledChild` at context/context_test.go:122:2
- 
- (Same nil source could also cause potential nil panic(s) at 1 other place(s): "context/context_test.go:124:9".)
- /opt/hostedtoolcache/go/1.21.6/x64/src/context/context_test.go:124:9: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- context/context.go:582:9: literal `nil` returned from `Done()` in position 0
- 	- context/context.go:105:2: returned as result 0 from interface method `Context.Done()` (implemented by `withoutCancelCtx.Done()`)
- 	- context/context_test.go:124:9: result 0 of `Done()` uninitialized; nil channel accessed via the assignment(s):
- 		- `WithValue(...)` to `precanceledChild` at context/context_test.go:122:2
- /opt/hostedtoolcache/go/1.21.6/x64/src/crypto/internal/randutil/randutil.go:34:9: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- randutil/randutil.go:16:2: nilable value assigned into global variable `closedChan`
- 	- randutil/randutil.go:34:9: global variable `closedChan` uninitialized; nil channel accessed
- /opt/hostedtoolcache/go/1.21.6/x64/src/crypto/tls/handshake_server_test.go:2050:9: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- context/context.go:184:9: literal `nil` returned from `Done()` in position 0
- 	- context/context.go:105:2: returned as result 0 from interface method `Context.Done()` (implemented by `emptyCtx.Done()`)
- 	- tls/handshake_server_test.go:2050:9: result 0 of `Done()` uninitialized; nil channel accessed
- /opt/hostedtoolcache/go/1.21.6/x64/src/crypto/tls/quic.go:417:9: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- context/context.go:184:9: literal `nil` returned from `Done()` in position 0
- 	- context/context.go:105:2: returned as result 0 from interface method `Context.Done()` (implemented by `emptyCtx.Done()`)
- 	- tls/conn.go:1510:20: result 0 of `Done()` assigned into field `cancelc` via the assignment(s):
- 		- `context.WithCancel(ctx)` to `handshakeCtx` at tls/conn.go:1503:2
- 	- tls/quic.go:417:9: field `cancelc` uninitialized; nil channel accessed
- 
- (Same nil source could also cause potential nil panic(s) at 1 other place(s): "tls/quic.go:407:9".)
- /opt/hostedtoolcache/go/1.21.6/x64/src/database/sql/ctxutil.go:21:10: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- context/context.go:184:9: literal `nil` returned from `Done()` in position 0
- 	- context/context.go:105:2: returned as result 0 from interface method `Context.Done()` (implemented by `emptyCtx.Done()`)
- 	- sql/ctxutil.go:21:10: result 0 of `Done()` uninitialized; nil channel accessed
- 
- (Same nil source could also cause potential nil panic(s) at 13 other place(s): "sql/ctxutil.go:40:9", "sql/ctxutil.go:57:9", "sql/ctxutil.go:74:9", "sql/ctxutil.go:91:9", "sql/sql.go:1219:10", "sql/sql.go:1336:10", "sql/sql.go:1290:9", "sql/sql.go:2174:4", "sql/sql.go:2210:9", "sql/sql.go:2255:9", "sql/sql.go:2966:9", "sql/sql.go:2963:9", and "sql/sql.go:2969:9".)
- /opt/hostedtoolcache/go/1.21.6/x64/src/database/sql/ctxutil.go:21:10: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- context/context.go:184:9: literal `nil` returned from `Done()` in position 0
- 	- context/context.go:105:2: returned as result 0 from interface method `Context.Done()` (implemented by `emptyCtx.Done()`)
- 	- sql/ctxutil.go:21:10: result 0 of `Done()` uninitialized; nil channel accessed
- 
- (Same nil source could also cause potential nil panic(s) at 17 other place(s): "sql/ctxutil.go:40:9", "sql/ctxutil.go:57:9", "sql/ctxutil.go:74:9", "sql/ctxutil.go:91:9", "sql/sql.go:1219:10", "sql/sql.go:1336:10", "sql/sql.go:1290:9", "sql/sql.go:2174:4", "sql/sql.go:2210:9", "sql/sql.go:2255:9", "sql/sql.go:2966:9", "sql/sql.go:2963:9", "sql/sql.go:2969:9", "sql/fakedb_test.go:692:11", "sql/fakedb_test.go:799:9", "sql/sql_test.go:345:9", and "sql/sql_test.go:3031:9".)
- /opt/hostedtoolcache/go/1.21.6/x64/src/database/sql/fakedb_test.go:287:3: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- sql/fakedb_test.go:290:17: literal `nil` assigned into field `waitingCh`
- 	- sql/fakedb_test.go:287:3: field `waitingCh` uninitialized; nil channel accessed
- /opt/hostedtoolcache/go/1.21.6/x64/src/database/sql/sql.go:1063:10: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- sql/sql.go:1070:19: literal `nil` assigned into field `cleanerCh`
- 	- sql/sql.go:1063:10: field `cleanerCh` uninitialized; nil channel accessed
- /opt/hostedtoolcache/go/1.21.6/x64/src/database/sql/sql.go:2966:9: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- sql/sql.go:2966:9: unassigned variable `txctxDone` uninitialized; nil channel accessed
- /opt/hostedtoolcache/go/1.21.6/x64/src/internal/fuzz/fuzz.go:225:10: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- context/context.go:184:9: literal `nil` returned from `Done()` in position 0
- 	- context/context.go:105:2: returned as result 0 from interface method `Context.Done()` (implemented by `emptyCtx.Done()`)
- 	- fuzz/fuzz.go:225:10: result 0 of `Done()` uninitialized; nil channel accessed via the assignment(s):
- 		- `context.WithTimeout(...)` to `ctx` at fuzz/fuzz.go:107:3,
- 		- `ctx.Done()` to `doneC` at fuzz/fuzz.go:114:2
- 
- (Same nil source could also cause potential nil panic(s) at 3 other place(s): "fuzz/worker.go:111:10", "fuzz/worker.go:776:10", and "fuzz/worker.go:1190:9".)
- /opt/hostedtoolcache/go/1.21.6/x64/src/internal/fuzz/fuzz.go:384:8: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- fuzz/fuzz.go:384:8: unassigned variable `inputC` uninitialized; nil channel accessed
- /opt/hostedtoolcache/go/1.21.6/x64/src/internal/fuzz/fuzz.go:388:8: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- fuzz/fuzz.go:388:8: unassigned variable `minimizeC` uninitialized; nil channel accessed
- /opt/hostedtoolcache/go/1.21.6/x64/src/internal/fuzz/worker.go:119:10: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- fuzz/worker.go:343:12: literal `nil` assigned into field `termC`
- 	- fuzz/worker.go:119:10: field `termC` uninitialized; nil channel accessed
- /opt/hostedtoolcache/go/1.21.6/x64/src/log/slog/logger_test.go:343:4: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- context/context.go:184:9: literal `nil` returned from `Done()` in position 0
- 	- context/context.go:105:2: returned as result 0 from interface method `Context.Done()` (implemented by `emptyCtx.Done()`)
- 	- slog/logger_test.go:343:4: result 0 of `Done()` uninitialized; nil channel accessed via the assignment(s):
- 		- `context.WithTimeout(...)` to `ctx` at slog/logger_test.go:333:2
- /opt/hostedtoolcache/go/1.21.6/x64/src/net/dial.go:592:10: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- context/context.go:184:9: literal `nil` returned from `Done()` in position 0
- 	- context/context.go:105:2: returned as result 0 from interface method `Context.Done()` (implemented by `emptyCtx.Done()`)
- 	- net/dial.go:592:10: result 0 of `Done()` uninitialized; nil channel accessed
- 
- (Same nil source could also cause potential nil panic(s) at 4 other place(s): "net/fd_unix.go:143:11", "net/fd_unix.go:63:10", "net/lookup.go:277:9", and "net/lookup.go:333:9".)
- /opt/hostedtoolcache/go/1.21.6/x64/src/net/dial.go:592:10: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- context/context.go:184:9: literal `nil` returned from `Done()` in position 0
- 	- context/context.go:105:2: returned as result 0 from interface method `Context.Done()` (implemented by `emptyCtx.Done()`)
- 	- net/dial.go:592:10: result 0 of `Done()` uninitialized; nil channel accessed
- 
- (Same nil source could also cause potential nil panic(s) at 6 other place(s): "net/fd_unix.go:143:11", "net/fd_unix.go:63:10", "net/lookup.go:277:9", "net/lookup.go:333:9", "net/dial_test.go:152:5", and "net/dial_unix_test.go:100:9".)
- /opt/hostedtoolcache/go/1.21.6/x64/src/net/http/h2_bundle.go:7666:12: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- context/context.go:184:9: literal `nil` returned from `Done()` in position 0
- 	- context/context.go:105:2: returned as result 0 from interface method `Context.Done()` (implemented by `emptyCtx.Done()`)
- 	- http/h2_bundle.go:7666:12: result 0 of `Done()` uninitialized; nil channel accessed via the assignment(s):
- 		- `http2shouldRetryRequest(...)` to `req` at http/h2_bundle.go:7652:7
- 
- (Same nil source could also cause potential nil panic(s) at 17 other place(s): "http/h2_bundle.go:8164:9", "http/h2_bundle.go:8396:10", "http/h2_bundle.go:8559:10", "http/h2_bundle.go:8513:11", "http/h2_bundle.go:8440:9", "http/h2_bundle.go:8578:9", "http/h2_bundle.go:8920:10", "http/h2_bundle.go:9696:9", "http/h2_bundle.go:10040:9", "http/server.go:2816:10", "http/server.go:3415:9", "http/transport.go:573:10", "http/transport.go:1407:11", "http/transport.go:1421:9", "http/transport.go:1727:10", "http/transport.go:2252:10", and "http/transport.go:2697:10".)
- /opt/hostedtoolcache/go/1.21.6/x64/src/net/http/h2_bundle.go:8552:10: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- http/h2_bundle.go:8552:10: literal `nil` uninitialized; nil channel accessed via the assignment(s):
- 		- `nil` to `respHeaderTimer` at http/h2_bundle.go:8556:4
- /opt/hostedtoolcache/go/1.21.6/x64/src/net/http/h2_bundle.go:8552:10: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- http/h2_bundle.go:8552:10: unassigned variable `respHeaderTimer` uninitialized; nil channel accessed
- /opt/hostedtoolcache/go/1.21.6/x64/src/net/http/h2_bundle.go:8554:10: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- http/h2_bundle.go:8554:10: literal `nil` uninitialized; nil channel accessed via the assignment(s):
- 		- `nil` to `respHeaderRecv` at http/h2_bundle.go:8555:4
- /opt/hostedtoolcache/go/1.21.6/x64/src/net/http/h2_bundle.go:8554:10: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- http/h2_bundle.go:8554:10: unassigned variable `respHeaderRecv` uninitialized; nil channel accessed
- /opt/hostedtoolcache/go/1.21.6/x64/src/net/http/pprof/pprof.go:113:9: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- context/context.go:184:9: literal `nil` returned from `Done()` in position 0
- 	- context/context.go:105:2: returned as result 0 from interface method `Context.Done()` (implemented by `emptyCtx.Done()`)
- 	- pprof/pprof.go:113:9: result 0 of `Done()` uninitialized; nil channel accessed
- 
- (Same nil source could also cause potential nil panic(s) at 1 other place(s): "pprof/pprof.go:300:9".)
- /opt/hostedtoolcache/go/1.21.6/x64/src/net/http/serve_test.go:4788:9: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- context/context.go:184:9: literal `nil` returned from `Done()` in position 0
- 	- context/context.go:105:2: returned as result 0 from interface method `Context.Done()` (implemented by `emptyCtx.Done()`)
- 	- http/serve_test.go:4788:9: result 0 of `Done()` uninitialized; nil channel accessed via the assignment(s):
- 		- `<-ctxc` to `ctx` at http/serve_test.go:4786:2
- /opt/hostedtoolcache/go/1.21.6/x64/src/net/http/transport.go:1405:11: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- context/context.go:184:9: literal `nil` returned from `Done()` in position 0
- 	- context/context.go:105:2: returned as result 0 from interface method `Context.Done()` (implemented by `emptyCtx.Done()`)
- 	- http/client_test.go:1332:15: result 0 of `Done()` assigned into field `Cancel` via the assignment(s):
- 		- `context.WithCancel(...)` to `ctx` at http/client_test.go:1322:2
- 	- http/transport.go:1405:11: field `Cancel` uninitialized; nil channel accessed
- /opt/hostedtoolcache/go/1.21.6/x64/src/net/http/transport.go:2669:10: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- http/transport.go:2669:10: literal `nil` uninitialized; nil channel accessed via the assignment(s):
- 		- `nil` to `pcClosed` at http/transport.go:2670:4
- /opt/hostedtoolcache/go/1.21.6/x64/src/net/http/transport.go:2677:10: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- http/transport.go:2677:10: unassigned variable `respHeaderTimer` uninitialized; nil channel accessed
- /opt/hostedtoolcache/go/1.21.6/x64/src/net/http/transport.go:2694:10: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- http/transport.go:2694:10: literal `nil` uninitialized; nil channel accessed via the assignment(s):
- 		- `nil` to `cancelChan` at http/transport.go:2696:4
- /opt/hostedtoolcache/go/1.21.6/x64/src/net/http/transport.go:2697:10: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- http/transport.go:2697:10: literal `nil` uninitialized; nil channel accessed via the assignment(s):
- 		- `nil` to `ctxDoneChan` at http/transport.go:2700:4
- /opt/hostedtoolcache/go/1.21.6/x64/src/net/net.go:688:2: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- net/net.go:680:5: nilable value assigned into global variable `threadLimit`
- 	- net/net.go:688:2: global variable `threadLimit` uninitialized; nil channel accessed
- /opt/hostedtoolcache/go/1.21.6/x64/src/os/exec/exec.go:664:10: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- context/context.go:184:9: literal `nil` returned from `Done()` in position 0
- 	- context/context.go:105:2: returned as result 0 from interface method `Context.Done()` (implemented by `emptyCtx.Done()`)
- 	- exec/exec.go:664:10: result 0 of `Done()` uninitialized; nil channel accessed
- 
- (Same nil source could also cause potential nil panic(s) at 1 other place(s): "exec/exec.go:760:9".)
- /opt/hostedtoolcache/go/1.21.6/x64/src/os/signal/example_unix_test.go:40:9: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- context/context.go:184:9: literal `nil` returned from `Done()` in position 0
- 	- context/context.go:105:2: returned as result 0 from interface method `Context.Done()` (implemented by `emptyCtx.Done()`)
- 	- signal/example_unix_test.go:40:9: result 0 of `Done()` uninitialized; nil channel accessed via the assignment(s):
- 		- `signal.NotifyContext(...)` to `ctx` at signal/example_unix_test.go:21:2
- /opt/hostedtoolcache/go/1.21.6/x64/src/os/signal/signal_test.go:728:5: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- context/context.go:184:9: literal `nil` returned from `Done()` in position 0
- 	- context/context.go:105:2: returned as result 0 from interface method `Context.Done()` (implemented by `emptyCtx.Done()`)
- 	- signal/signal_test.go:728:5: result 0 of `Done()` uninitialized; nil channel accessed via the assignment(s):
- 		- `NotifyContext(...)` to `ctx` at signal/signal_test.go:715:3
- 
- (Same nil source could also cause potential nil panic(s) at 4 other place(s): "signal/signal_test.go:801:9", "signal/signal_test.go:822:9", "signal/signal_test.go:844:9", and "signal/signal_test.go:872:9".)
- /opt/hostedtoolcache/go/1.21.6/x64/src/reflect/all_test.go:1701:3: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- reflect/all_test.go:1701:3: unassigned variable `c` uninitialized; nil channel accessed
- 
- (Same nil source could also cause potential nil panic(s) at 7 other place(s): "reflect/all_test.go:1695:13", "reflect/all_test.go:1690:16", "reflect/all_test.go:1680:10", "reflect/all_test.go:1678:3", "reflect/all_test.go:1669:3", "reflect/all_test.go:1657:3", and "reflect/all_test.go:1652:13".)
- /opt/hostedtoolcache/go/1.21.6/x64/src/runtime/abi_test.go:27:2: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- runtime/abi_test.go:23:5: nilable value assigned into global variable `regConfirmRun`
- 	- runtime/abi_test.go:27:2: global variable `regConfirmRun` uninitialized; nil channel accessed
- /opt/hostedtoolcache/go/1.21.6/x64/src/runtime/cgocall.go:306:5: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- runtime/proc.go:129:5: nilable value assigned into global variable `main_init_done`
- 	- runtime/cgocall.go:306:5: global variable `main_init_done` uninitialized; nil channel accessed
- /opt/hostedtoolcache/go/1.21.6/x64/src/runtime/signal_unix.go:202:3: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- runtime/signal_unix.go:94:2: nilable value assigned into global variable `enableSigChan`
- 	- runtime/signal_unix.go:202:3: global variable `enableSigChan` uninitialized; nil channel accessed
- /opt/hostedtoolcache/go/1.21.6/x64/src/runtime/signal_unix.go:203:5: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- runtime/signal_unix.go:95:2: nilable value assigned into global variable `maskUpdatedChan`
- 	- runtime/signal_unix.go:203:5: global variable `maskUpdatedChan` uninitialized; nil channel accessed
- /opt/hostedtoolcache/go/1.21.6/x64/src/runtime/signal_unix.go:227:3: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- runtime/signal_unix.go:93:2: nilable value assigned into global variable `disableSigChan`
- 	- runtime/signal_unix.go:227:3: global variable `disableSigChan` uninitialized; nil channel accessed
- /opt/hostedtoolcache/go/1.21.6/x64/src/time/example_test.go:156:14: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- time/example_test.go:150:5: nilable value assigned into global variable `c`
- 	- time/example_test.go:156:14: global variable `c` uninitialized; nil channel accessed

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (9b1d75d) 88.33% compared to head (fe6b551) 88.31%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #193      +/-   ##
==========================================
- Coverage   88.33%   88.31%   -0.03%     
==========================================
  Files          55       55              
  Lines        9364     9344      -20     
==========================================
- Hits         8272     8252      -20     
  Misses        917      917              
  Partials      175      175              

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[sonalmahajan15]

As discussed internally, we did agree upon this strategy to address false positives. LGTM!

[sonalmahajan15]

Unrelated to the PR, I guess, but a welcome change :)

[yuxincs]

Yes :)