[nzakas]

Adds shell/no-expansions-in-single-quotes, which mirrors ShellCheck SC2016. Expansions don't happen inside single quotes, so '$var' is almost always a mistake.

Behavior

• Reports a single-quoted string that contains $name, ${...}, $(...), or a backtick pair.
• Not reported:
  • Positional-style references such as $1, so awk and sed programs like awk '{print $1}' stay clean.
  • A lone $ followed by a digit or punctuation ('costs $5').
  • $'...' strings.
• No autofix: switching to double quotes can change the meaning of other characters in the string.
• Recommended config: "warn", not "error", because single-quoting literal $ text is sometimes intentional (for example, text passed to another program).

Documentation

Adds docs/rules/no-expansions-in-single-quotes.md, following the format of the @eslint/json, @eslint/css, and @eslint/markdown rule docs: description, background, rule details with incorrect and correct examples, options, when not to use it, and the ShellCheck reference. The rule's meta.docs.url points at that file, and its README table entry links to it.

Testing

9 RuleTester cases and 5 documentation checks (191 total); build, lint, and format checks pass.

🤖 Generated with Claude Code

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Summary by CodeRabbit

• New Features

  • Added the no-expansions-in-single-quotes rule, which warns about variable, parameter, command, and backtick-style expansions inside single-quoted strings.
  • Enabled the rule in the recommended Bash configuration at warning level.
  • Includes exceptions for positional references, literal dollar signs, and ANSI-C quoting.

• Documentation

  • Added usage guidance, examples, configuration details, and a ShellCheck SC2016 reference for the new rule.

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• README.md
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• src/index.ts
• src/rules/no-expansions-in-single-quotes.spec.ts
• src/rules/no-expansions-in-single-quotes.ts

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• README.md
• docs/rules/no-expansions-in-single-quotes.md
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• src/index.ts
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• src/rules/no-expansions-in-single-quotes.ts

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📝 Walkthrough

Walkthrough

This change adds the no-expansions-in-single-quotes rule. The rule detects expansion-like syntax in single-quoted strings, is enabled in the recommended configuration, has test coverage, and is documented with its ShellCheck SC2016 mapping.

Changes

Single-quoted expansion rule

Layer / File(s)	Summary
Rule implementation and validation src/rules/no-expansions-in-single-quotes.ts, src/rules/no-expansions-in-single-quotes.spec.ts	The new rule reports variable, parameter, command, and backtick expansion-like syntax in single-quoted strings. Tests cover valid exclusions, invalid cases, and diagnostic locations.
Plugin registration src/index.ts, src/index.spec.ts	The rule is exported and enabled as a warning in the recommended Bash configuration. The entry-point test verifies both exported rules.
Rule documentation docs/rules/no-expansions-in-single-quotes.md, README.md	Documentation describes detection behavior, exclusions, examples, configuration, severity, and the ShellCheck SC2016 mapping.

Estimated code review effort: 2 (Simple) | ~15 minutes

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[Copilot]

Copilot review overview

🟡 Changes recommended

Empty backtick command substitutions are valid but currently evade the documented detection behavior.

Review effort: Balanced
Findings: 1

Open (1)

• Empty backtick command substitutions are not flagged · New

What changed in this PR

Adds a ShellCheck SC2016-inspired rule detecting expansion-like syntax inside single-quoted Bash strings.

Changes:

• Implements and tests the new rule.
• Enables it as a recommended warning.
• Adds rule documentation and README coverage.

File	Description
src/​rules/​no-expansions-in-single-quotes.ts	Implements expansion detection.
src/​rules/​no-expansions-in-single-quotes.spec.ts	Adds rule tests.
src/​index.ts	Registers and configures the rule.
src/​index.spec.ts	Verifies rule exposure.
README.md	Lists the new rule.
docs/​rules/​no-expansions-in-single-quotes.md	Documents behavior and usage.

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