Support for "always safe" for error returning and ok-form functions

[sonalmahajan15]

This PR adds support for "always safe" case for rich check effect functions, namely error returning functions and ok-form functions.

The support for always safe tracking is currently limited to:

1. directly determinable cases of "non-nil" return

      (a) return &S{}, errors.New(...)  // supported
      (b) return new(S), errors.New(...)  // supported
      (c) if s != nil {
               return s, errors.New(...)  // supported
          }
  
      (d) return getS(), errors.New(...)  // not supported
      (e) return x.y.z.f, errors.New(...)   // not supported

2. immediate function call only

func errRetFunc() (*S, error) {
      return &S{}, errors.New(...)
}

func wrapErrRetFunc() (*S, error) {
      return errRetFunc()
}

func test1() {
       // supported
       v, _ := errRetFunc()    // immediate function call, supported
       _ = *v

       // not supported
       v, _ := wrapErrRetFunc()  // multiple hops, not supported
       _ = *v
}

[closes #151 , #199 ]

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.64%. Comparing base (28b542b) to head (5ec951b).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #264      +/-   ##
==========================================
+ Coverage   87.51%   87.64%   +0.13%     
==========================================
  Files          63       63              
  Lines        7842     7927      +85     
==========================================
+ Hits         6863     6948      +85     
  Misses        799      799              
  Partials      180      180              

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[github-actions]

Golden Test

Warning

❌ NilAway errors reported on stdlib are different 📉.

3283 errors on base branch (main, 28b542b)
3275 errors on test branch (d830871)

Diffs

- /opt/hostedtoolcache/go/1.22.5/x64/src/encoding/base32/base32_test.go:114:41: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- base32/base32_test.go:114:41: result 0 of `AppendDecode()` lacking guarding; sliced into via the assignment(s):
- 		- `StdEncoding.AppendDecode(...)` to `dst` at base32/base32_test.go:110:3
- /opt/hostedtoolcache/go/1.22.5/x64/src/encoding/base64/base64_test.go:173:37: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- base64/base64_test.go:173:37: result 0 of `AppendDecode()` lacking guarding; sliced into via the assignment(s):
- 		- `tt.enc.AppendDecode(...)` to `dst` at base64/base64_test.go:169:4
- /opt/hostedtoolcache/go/1.22.5/x64/src/go/parser/parser.go:2195:29: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- parser/parser.go:2249:36: result 0 of `parseSimpleStmt()` lacking guarding; passed as arg `s` to `isTypeSwitchGuard()` via the assignment(s):
- 		- `p.parseSimpleStmt(...)` to `s2` at parser/parser.go:2243:5
- 	- parser/parser.go:2195:29: function parameter `s` accessed field `X`
- /opt/hostedtoolcache/go/1.22.5/x64/src/net/http/cookiejar/jar.go:204:11: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- cookiejar/jar_test.go:1347:13: result 0 of `New()` lacking guarding; used as receiver to call `Cookies()` via the assignment(s):
- 		- `New(nil)` to `jar` at cookiejar/jar_test.go:1345:3
- 	- cookiejar/jar.go:158:9: read by method receiver `j` used as receiver to call `cookies()`
- 	- cookiejar/jar.go:204:11: read by method receiver `j` accessed field `entries`
- /opt/hostedtoolcache/go/1.22.5/x64/src/net/http/cookiejar/jar.go:204:11: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- cookiejar/jar_test.go:1351:13: result 0 of `New()` lacking guarding; used as receiver to call `Cookies()` via the assignment(s):
- 		- `New(nil)` to `jar` at cookiejar/jar_test.go:1345:3
- 	- cookiejar/jar.go:158:9: read by method receiver `j` used as receiver to call `cookies()`
- 	- cookiejar/jar.go:204:11: read by method receiver `j` accessed field `entries`
- /opt/hostedtoolcache/go/1.22.5/x64/src/net/http/cookiejar/jar.go:291:11: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- cookiejar/jar_test.go:1350:3: result 0 of `New()` lacking guarding; used as receiver to call `SetCookies()` via the assignment(s):
- 		- `New(nil)` to `jar` at cookiejar/jar_test.go:1345:3
- 	- cookiejar/jar.go:233:2: read by method receiver `j` used as receiver to call `setCookies()`
- 	- cookiejar/jar.go:291:11: read by method receiver `j` accessed field `entries`
- /opt/hostedtoolcache/go/1.22.5/x64/src/net/url/example_test.go:157:2: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- url/url.go:1123:9: result 0 of `ParseQuery()` lacking guarding; returned from `Query()` in position 0 via the assignment(s):
- 		- `ParseQuery(...)` to `v` at url/url.go:1122:2
- 	- url/example_test.go:157:2: result 0 of `Query()` called `Set()` via the assignment(s):
- 		- `url.Parse(...)` to `u` at url/example_test.go:150:2,
- 		- `u.Query()` to `q` at url/example_test.go:156:2
- 
- (Same nil source could also cause potential nil panic(s) at 3 other place(s): "url/example_test.go:158:15", "url/example_test.go:308:14", and "url/example_test.go:309:14".)
- /opt/hostedtoolcache/go/1.22.5/x64/src/net/url/url_test.go:1307:13: Potential nil panic detected. Observed nil flow from source to dereference point: 
- 	- url/url.go:1123:9: result 0 of `ParseQuery()` lacking guarding; returned from `Query()` in position 0 via the assignment(s):
- 		- `ParseQuery(...)` to `v` at url/url.go:1122:2
- 	- url/url_test.go:1307:13: result 0 of `Query()` called `Get()` via the assignment(s):
- 		- `Parse(...)` to `u` at url/url_test.go:1302:2,
- 		- `u.Query()` to `v` at url/url_test.go:1303:2
- 
- (Same nil source could also cause potential nil panic(s) at 9 other place(s): "url/url_test.go:1311:13", "url/url_test.go:1314:13", "url/url_test.go:1317:13", "url/url_test.go:1320:13", "url/url_test.go:1323:13", "url/url_test.go:1326:13", "url/url_test.go:1329:13", "url/url_test.go:1332:2", and "url/url_test.go:1333:13".)

[yuxincs]

Use slices.DeleteFunc to modify the slice in-place?

[sonalmahajan15]

Good idea. Done :)

[yuxincs]

remove this comment?

[sonalmahajan15]

Yeah, makes sense, it has become redundant now. Done.