x/tools/gopls: impossible SEGV in Scanner.next

[adonovan]

#!stacks
"goPanicIndex" && "scanner.(*Scanner).next:+7"

Issue created by stacks.

Yet more blatant memory corruption:

func (s *Scanner) next() {
	if s.rdOffset < len(s.src) {
		s.offset = s.rdOffset
		...
		r, w := rune(s.src[s.rdOffset]), 1 // <--- SEGV

Weirdly though, we got two almost identical reports of this in the same day's batch.

This stack 8RmGzg was reported by telemetry:

• crash/crash
• runtime.gopanic:+69,+0x167
• go/parser.ParseFile.func1:+5,+0x3d7
• runtime.gopanic:+50,+0x131
• runtime.goPanicIndex:+2,+0x73
• go/scanner.(*Scanner).next:+7,+0x196
• go/scanner.(*Scanner).Scan:+35,+0xd6
• go/parser.(*parser).next0:+18,+0x184
• go/parser.(*parser).next:+4,+0x64
• go/parser.(*parser).parseOperand:+12,+0x17a
• go/parser.(*parser).parsePrimaryExpr:+6,+0x132
• go/parser.(*parser).parseUnaryExpr:+68,+0x39d
• go/parser.(*parser).parseBinaryExpr:+6,+0x149
• go/parser.(*parser).parseExpr:+5,+0xd4
• go/parser.(*parser).parseRhs:=1892,+0x1d8
• go/parser.(*parser).parseCallOrConversion:+10,+0x175
• go/parser.(*parser).parsePrimaryExpr:+40,+0x33a
• go/parser.(*parser).parseUnaryExpr:+68,+0x39d

golang.org/x/tools/gopls@v0.20.0 go1.24.6 windows/amd64 vscode (1)

Dups: xc6nww

[adonovan]

This stack xc6nww was reported by telemetry:

• crash/crash
• runtime.gopanic:+69,+0x167
• go/parser.ParseFile.func1:+5,+0x3d7
• runtime.gopanic:+50,+0x131
• runtime.goPanicIndex:+2,+0x73
• go/scanner.(*Scanner).next:+7,+0x196
• go/scanner.(*Scanner).skipWhitespace:+2,+0x19
• go/scanner.(*Scanner).Scan:+10,+0x38
• go/parser.(*parser).next0:+18,+0x184
• go/parser.(*parser).consumeComment:+14,+0x13a
• go/parser.(*parser).consumeCommentGroup:+5,+0x26d
• go/parser.(*parser).next:+24,+0x304
• go/parser.(*parser).expectSemi:+16,+0xc7
• go/parser.(*parser).parseFieldDecl:+85,+0x531
• go/parser.(*parser).parseStructType:+12,+0x184
• go/parser.(*parser).tryIdentOrType:+14,+0x355
• go/parser.(*parser).parseType:+5,+0xcb

golang.org/x/tools/gopls@v0.20.0 go1.24.6 windows/amd64 vscode (1)

[gabyhelp]

Related Issues

• x/tools/gopls: impossible SEGV in DecodeRune #76252
• x/tools/gopls: SEGV in go/types due to invalid pointer in BinaryExpr.Y #76238
• x/tools/go/ast/inspector: panics on Node slice of 32M entries #74498
• x/tools/gopls: nil deref in (*types.Package).Path within gcimporter #76222
• x/tools/gopls: Parse: crash in fixInitStmt #72026 (closed)
• x/tools/gopls: objectpath: panic due to nil *types.Signature #75575
• x/tools/gopls: SEGV in ParseDiagnostics (corrupt g or SP) #75464
• x/tools/gopls: OOM reported by fatal in runtime.mallocgc (windows) #70445 (closed)
• x/tools/gopls: crash on multiline gotmpl comments #74635 (closed)
• x/tools/gopls: DidChangeWatchedFiles: impossible crash in growslice #75465

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