fix(preprocess): avoid shadowing of iota

[Villaquiranm]

closes #5876

[Gno2D2]

🛠 PR Checks Summary

🔴 Pending initial approval by a review team member, or review from tech-staff

Manual Checks (for Reviewers):

• IGNORE the bot requirements for this PR (force green CI check)

Read More

🤖 This bot helps streamline PR reviews by verifying automated checks and providing guidance for contributors and reviewers.

✅ Automated Checks (for Contributors):

🟢 Maintainers must be able to edit this pull request (more info)
🔴 Pending initial approval by a review team member, or review from tech-staff

☑️ Contributor Actions:

1. Fix any issues flagged by automated checks.
2. Follow the Contributor Checklist to ensure your PR is ready for review.
   • Add new tests, or document why they are unnecessary.
   • Provide clear examples/screenshots, if necessary.
   • Update documentation, if required.
   • Ensure no breaking changes, or include BREAKING CHANGE notes.
   • Link related issues/PRs, where applicable.

☑️ Reviewer Actions:

1. Complete manual checks for the PR, including the guidelines and additional checks if applicable.

📚 Resources:

• Report a bug with the bot.
• View the bot’s configuration file.

Debug

Automated Checks

Maintainers must be able to edit this pull request (more info)

If

🟢 Condition met
└── 🟢 And
    ├── 🟢 The base branch matches this pattern: ^master$
    └── 🟢 The pull request was created from a fork (head branch repo: Villaquiranm/gno)

Then

🟢 Requirement satisfied
└── 🟢 Maintainer can modify this pull request

Pending initial approval by a review team member, or review from tech-staff

If

🟢 Condition met
└── 🟢 And
    ├── 🟢 The base branch matches this pattern: ^master$
    └── 🟢 Not (🔴 Pull request author is a member of the team: tech-staff)

Then

🔴 Requirement not satisfied
└── 🔴 If
    ├── 🔴 Condition
    │   └── 🔴 Or
    │       ├── 🔴 At least one of these user(s) reviewed the pull request: [aronpark1007 davd-gzl jefft0 notJoon omarsy MikaelVallenet] (with state "APPROVED")
    │       ├── 🔴 At least 1 user(s) of the team tech-staff reviewed pull request
    │       └── 🔴 This pull request is a draft
    └── 🔴 Else
        └── 🔴 And
            ├── 🟢 This label is applied to pull request: review/triage-pending
            └── 🔴 On no pull request

Manual Checks

**IGNORE** the bot requirements for this PR (force green CI check)

If

🟢 Condition met
└── 🟢 On every pull request

Can be checked by

• Any user with comment edit permission

[davd-gzl]

[AI bot]

Verified on af3accb: gno lint rejects a package whose exported function takes an iota parameter, as gnoPreprocessError, matching the VM even though go/types accepts the source. Nested const groups still evaluate iota exactly as the Go compiler does.

main / build is red only on formatting: four of the new filetests end with a trailing blank line. docs is red on an unreachable link in gnoland-networks.md, which this branch does not touch.

Full review: https://github.com/samouraiworld/gno-agent-workspace/blob/main/reviews/pr/5xxx/5981-avoid-shadowing-iota/2-af3accbce/review_claude-opus-4-8_davd-gzl.md

[davd-gzl]

A three-clause for init never reaches this check. initStaticBlocks1 renames those names, and their body references, to <name>.loopvar, and it runs before Reserve sees them. So for iota := 0; iota < 2; iota++ { println(iota) } prints 0 and 1, while for iota := range s is rejected.

repro

# from a local clone of gnolang/gno:
gh pr checkout 5981 -R gnolang/gno
cat > gnovm/tests/files/iota_forinit.gno <<'EOF'
package main

func main() {
	for iota := 0; iota < 2; iota++ {
		println(iota)
	}
}

// Error:
// main/iota_forinit.gno:4:6-14: builtin identifiers cannot be shadowed: iota
EOF
go test -run 'TestFiles/iota_forinit.gno$' ./gnovm/pkg/gnolang/
rm gnovm/tests/files/iota_forinit.gno

--- FAIL: TestFiles (0.03s)
    --- FAIL: TestFiles/iota_forinit.gno (0.00s)
        files_test.go:135: unexpected output:
            0
            1

FAIL
FAIL	github.com/gnolang/gno/gnovm/pkg/gnolang	0.044s

[davd-gzl]

func f(iota int) { println("hi") }, func f() (iota int) and func (iota T) M() all run on master, because the name is bound but never referenced. Node startup re-preprocesses every stored package at VMKeeper.Initialize, with no per-package recover. A package already on chain that uses one of those forms would fail at boot rather than at its next call.

repro

# from a local clone of gnolang/gno:
gh pr checkout 5981 -R gnolang/gno
cat > iota_param.gno <<'EOF'
package main

func f(iota int) { println("hi") }

func main() { f(3) }
EOF
echo "== at PR head:"; go run ./gnovm/cmd/gno run iota_param.gno
git checkout $(git merge-base origin/master HEAD) -- gnovm/pkg/gnolang/nodes.go
echo "== with the check removed:"; go run ./gnovm/cmd/gno run iota_param.gno
git checkout HEAD -- gnovm/pkg/gnolang/nodes.go
rm iota_param.gno

== at PR head:
panic: builtin identifiers cannot be shadowed: iota [recovered]
	panic: main/iota_param.gno:3:1-35: builtin identifiers cannot be shadowed: iota:
	--- preprocess stack ---
== with the check removed:
hi

[davd-gzl]

Nit: func f(len int) int { return len } compiles here, and so does every uverse name but iota in that position. The message says builtin identifiers cannot be shadowed, so an author who hits it on a parameter reads a rule the compiler does not enforce.