x/tools/go/analysis/passes/httpresponse: unrecognized failures

[gopherbot]

#!watchflakes
post <- pkg == "golang.org/x/tools/go/analysis/passes/httpresponse" && test == ""

Issue created automatically to collect these failures.

Example (log):

panic: runtime error: invalid memory address or nil pointer dereference [recovered]
	panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x5 pc=0x18354]

goroutine 119 [running]:
go/types.(*Checker).handleBailout(0xc0002f7e00, 0xc000115b40)
	/workdir/go/src/go/types/check.go:335 +0xc0
panic({0x2ac2c0?, 0x4c4300?})
	/workdir/go/src/runtime/panic.go:914 +0x27c
go/types.(*Scope).Lookup(...)
...
sync.(*Once).doSlow(0x0?, 0x0?)
	/workdir/go/src/sync/once.go:74 +0x110
sync.(*Once).Do(...)
	/workdir/go/src/sync/once.go:65
golang.org/x/tools/go/packages.(*loader).loadRecursive(0x0?, 0x0?)
	/workdir/gopath/src/golang.org/x/tools/go/packages/packages.go:839 +0x80
golang.org/x/tools/go/packages.(*loader).loadRecursive.func1.1(0x0?)
	/workdir/gopath/src/golang.org/x/tools/go/packages/packages.go:846 +0x40
created by golang.org/x/tools/go/packages.(*loader).loadRecursive.func1 in goroutine 114
	/workdir/gopath/src/golang.org/x/tools/go/packages/packages.go:845 +0x98

— watchflakes

[gopherbot]

Found new dashboard test flakes for:

#!watchflakes
post <- pkg == "golang.org/x/tools/go/analysis/passes/httpresponse" && test == ""

2023-05-01 14:33 linux-ppc64le-buildlet tools@7590fe4d go@069f9fb2 x/tools/go/analysis/passes/httpresponse (log)

panic: runtime error: invalid memory address or nil pointer dereference [recovered]
	panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x5 pc=0x18354]

goroutine 119 [running]:
go/types.(*Checker).handleBailout(0xc0002f7e00, 0xc000115b40)
	/workdir/go/src/go/types/check.go:335 +0xc0
panic({0x2ac2c0?, 0x4c4300?})
	/workdir/go/src/runtime/panic.go:914 +0x27c
go/types.(*Scope).Lookup(...)
...
sync.(*Once).doSlow(0x0?, 0x0?)
	/workdir/go/src/sync/once.go:74 +0x110
sync.(*Once).Do(...)
	/workdir/go/src/sync/once.go:65
golang.org/x/tools/go/packages.(*loader).loadRecursive(0x0?, 0x0?)
	/workdir/gopath/src/golang.org/x/tools/go/packages/packages.go:839 +0x80
golang.org/x/tools/go/packages.(*loader).loadRecursive.func1.1(0x0?)
	/workdir/gopath/src/golang.org/x/tools/go/packages/packages.go:846 +0x40
created by golang.org/x/tools/go/packages.(*loader).loadRecursive.func1 in goroutine 114
	/workdir/gopath/src/golang.org/x/tools/go/packages/packages.go:845 +0x98

— watchflakes

[timothy-king]

@griesemer @findleyr This looks like a go/types flake.

[findleyr]

This panic indicates that check.scope is nil during type-checking... not sure how that is possible.

[adonovan]

I agree, it is weird. The crash is reported in Lookup, whose only (noninlined) possible nil panic is the s dereference, but the call stack shows the parent is LookupParent, which only calls it with a non-nil s.

goroot/src/go/types/scope.go:

// Lookup returns the object in scope s with the given name if such an
// object exists; otherwise the result is nil.
func (s *Scope) Lookup(name string) Object {
	return resolve(name, s.elems[name]) // panic: nil deref here
}

// LookupParent follows the parent chain of scopes starting with s until
// it finds a scope where Lookup(name) returns a non-nil object, and then
// returns that scope and object. If a valid position pos is provided,
// only objects that were declared at or before pos are considered.
// If no such scope and object exists, the result is (nil, nil).
//
// Note that obj.Parent() may be different from the returned scope if the
// object was inserted into the scope and already had a parent at that
// time (see Insert). This can only happen for dot-imported objects
// whose scope is the scope of the package that exported them.
func (s *Scope) LookupParent(name string, pos token.Pos) (*Scope, Object) {
	for ; s != nil; s = s.parent {
		if obj := s.Lookup(name); obj != nil && (!pos.IsValid() || cmpPos(obj.scopePos(), pos) <= 0) { // Lookup called here
			return s, obj
		}
	}
	return nil, nil
}

The ppc assembly looks fine to me. Perhaps one of the compiler+runtime folks can take a look.

TEXT go/types.(*Scope).LookupParent(SB) /Users/adonovan/w/goroot/src/go/types/scope.go
prolog:
  scope.go:86           0x2ada90                eade0010                MOVD 16(R30),R22                        
  scope.go:86           0x2ada94                7c360840                CMPU R22,R1                             
  scope.go:86           0x2ada98                41800030                BLT 0x2adac8    body  

stack check:                      
  scope.go:86           0x2ada9c                f8610020                MOVD R3,32(R1)                          
  scope.go:86           0x2adaa0                f8810028                MOVD R4,40(R1)                          
  scope.go:86           0x2adaa4                f8a10030                MOVD R5,48(R1)                          
  scope.go:86           0x2adaa8                f8c10038                MOVD R6,56(R1)                          
  scope.go:86           0x2adaac                7ca802a6                MOVD LR,R5                              
  scope.go:86           0x2adab0                4bdd3f01                CALL runtime.morestack_noctxt.abi0(SB)  
  scope.go:86           0x2adab4                e8610020                MOVD 32(R1),R3                          
  scope.go:86           0x2adab8                e8810028                MOVD 40(R1),R4                          
  scope.go:86           0x2adabc                e8a10030                MOVD 48(R1),R5                          
  scope.go:86           0x2adac0                e8c10038                MOVD 56(R1),R6                          
  scope.go:86           0x2adac4                4bffffcc                BR go/types.(*Scope).LookupParent(SB)   

body (loop header):   r3=s
  scope.go:86           0x2adac8                7fe802a6                MOVD LR,R31                             
  scope.go:86           0x2adacc                fbe1ffa9                MOVDU R31,-88(R1)                       
  scope.go:86           0x2adad0                f8c10090                MOVD R6,144(R1)                         
  scope.go:86           0x2adad4                f8a10088                MOVD R5,136(R1)                         
  scope.go:86           0x2adad8                f8810080                MOVD R4,128(R1)                         
  scope.go:87           0x2adadc                48000018                BR 0x2adaf4  looptest
loophead:                           
  scope.go:87           0x2adae0                e9010050                MOVD 80(R1),R8                          
  scope.go:87           0x2adae4                e8680000                MOVD 0(R8),R3   load s indirectly from stack
  scope.go:73           0x2adae8                e8810080                MOVD 128(R1),R4                         
  scope.go:73           0x2adaec                e8a10088                MOVD 136(R1),R5                         
  position.go:88        0x2adaf0                7ce63b78                OR R7,R7,R6                             
looptest:
  scope.go:87           0x2adaf4                7c230000                CMP R3,R0                               
  scope.go:87           0x2adaf8                418200bc                BEQ 0x2adbb4      if s == nil return
  scope.go:87           0x2adafc                f8610050                MOVD R3,80(R1)       spill s  
# --- this is the range of lines reported in the crash ---             
  scope.go:73           0x2adb00                e8e30028                MOVD 40(R3),R7     s.elems                      
  scope.go:73           0x2adb04                7ca62b78                OR R5,R5,R6                        
  scope.go:73           0x2adb08                7c852378                OR R4,R4,R5                             
  scope.go:73           0x2adb0c                7ce43b78                OR R7,R7,R4                             
  scope.go:73           0x2adb10                3c600094                ADDIS $0,$148,R3                        
  scope.go:73           0x2adb14                38633020                ADD R3,$12320,R3                        
  scope.go:73           0x2adb18                4bd74429                CALL runtime.mapaccess1_faststr(SB)     
  scope.go:73           0x2adb1c                e8a30000                MOVD 0(R3),R5                   
  scope.go:73           0x2adb20                e8c30008                MOVD 8(R3),R6                           
  scope.go:73           0x2adb24                e8610080                MOVD 128(R1),R3   unspill s                       
  scope.go:73           0x2adb28                e8810088                MOVD 136(R1),R4                         
  scope.go:73           0x2adb2c                48000ab5                CALL go/types.resolve(SB)               
# ---
  ...

[findleyr]

CC @golang/runtime

[bcmills]

Duplicate of #37602