golang/go

x/tools/cmd/goyacc: bad code generated by goyacc for large grammars (more than 1000 non-terminals)

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#78251 opened on Mar 20, 2026

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Description

Go version

go version go1.26.1 darwin/arm64

Output of go env in your module/workspace:

AR='ar'
CC='cc'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='c++'
GCCGO='gccgo'
GO111MODULE=''
GOARCH='arm64'
GOARM64='v8.0'
GOAUTH='netrc'
GOBIN=''
GOCACHE='/Users/deepak/Library/Caches/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/Users/deepak/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/yw/mq1pwdbx3gd9077rsc65x7jw0000gn/T/go-build4184327577=/tmp/go-build -gno-record-gcc-switches -fno-common'
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMOD='/Users/deepak/src/varonis/dev.azure.com/VaronisIO/DA Cloud/pg-parser/go.mod'
GOMODCACHE='/Users/deepak/go/pkg/mod'
GONOPROXY='github.com/cyralinc/*,dev.azure.com/VaronisIO/*,github.com/lestrrat-go/*'
GONOSUMDB='github.com/cyralinc/*,dev.azure.com/VaronisIO/*'
GOOS='darwin'
GOPATH='/Users/deepak/go'
GOPRIVATE='github.com/cyralinc/*,dev.azure.com/VaronisIO/*'
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/opt/homebrew/Cellar/go/1.26.1/libexec'
GOSUMDB='sum.golang.org'
GOTELEMETRY='local'
GOTELEMETRYDIR='/Users/deepak/Library/Application Support/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/opt/homebrew/Cellar/go/1.26.1/libexec/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.26.1'
GOWORK=''

What did you do?

Run goyacc on a large grammar

What did you see happen?

When the number of non-terminals in the grammar is < 1000, the generated code behaves fine but the generated code fails to parse even simple inputs when the number of non-terminals is >= 1000. I confirmed that changing the value of the constant NOMORE to something like -1000000 from -1000 fixes the issue. This appears to be a sentinel value which should have a larger absolute value than the number of non-terminals in the grammar.

The number of states etc., were all within limits of the other defined constant values in the code.

What did you expect to see?

The generated code should work fine for a large number of non-terminal symbols in the grammar. 1000 definitely is not a very large number.

Contributor guide

Tech stack
go
Domain
tooling
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
under 1 hour
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
basic Go knowledgefamiliarity with goyacc
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
90
Research direction
The issue identifies that the constant NOMORE in goyacc source code has a value of 1000, which fails when grammars have 1000 or more non terminals. The fix involves increasing the absolute value of NOMORE or making it dynamically computed based on grammar size. The relevant file is likely in x/tools/cmd/goyacc/. Maintainers should review the constant usage and decide on a safe sentinel value.