Bashrs Makefile Linting: False Positives & Improvements

Hey guys, let's dive into some interesting challenges when using bashrs to lint Makefiles. As you know, Makefiles are super important for automating builds and tasks, but sometimes, the tools we use to check them can get a little confused. That's what we're going to explore here, focusing on how bashrs can sometimes generate false positives and offer suggestions that don't quite fit the Makefile context. It's all about making the process smoother and more accurate!

The Environment: Setting the Stage

Before we jump in, let's set the scene. We're looking at bashrs version 0.3.1+, which is the latest version at the time of this writing. The file type we're examining is a GNU Makefile. The shell specified within the Makefile is /bin/bash, declared using SHELL := /bin/bash. This setup helps to ensure that we're all on the same page and the issues are clearly defined within this environment.

Issue 1: "Local" in Strings: A False Alarm

One of the first issues we bump into is how bashrs handles the word "local." In shell scripting, "local" is a keyword used within functions. However, when "local" appears inside a string, as it might in a comment or a message, bashrs flags it as an error. For example, consider this snippet:

serve: ## Serve built files locally on port 8080
	@printf 'Starting local server on port 8080...\n'

Here, the line is perfectly valid; the word "local" is part of a string meant to inform the user. Yet, bashrs throws an error: SC2168: 'local' is only valid in functions. This is a false positive. The tool is mistaking a word in a string for a shell keyword. To get around this, you might have to rephrase the string, which is not ideal. A suggestion would be for bashrs to recognize that words within quoted strings are not meant to be shell keywords, avoiding these unnecessary flags.

Issue 2: Variable Expansion Warnings

Makefiles use a special syntax to pass shell variables. For instance, you might see $VAR to refer to a shell variable within a recipe. bashrs, however, often misunderstands this, warning about the use of $VAR. Consider the following example:

validate-makefile:
	@CODE=$?; \
	if [ $CODE -eq 0 ]; then \
		echo "Success";
	fi

In Makefiles, $ is how we escape the $ to pass it to the shell. This is valid and necessary syntax, and bashrs shouldn’t flag it. The tool generates warnings such as SC2082: To expand via indirection, use ${!name} or eval. $ is the PID, not indirection, SC2086: Double quote to prevent globbing and word splitting on $CODE, and SC2154: Variable 'CODE' is referenced but not assigned. These warnings are misleading because they don't apply to the context of a Makefile. The variable CODE is assigned within the recipe itself, and $ is intentionally used to escape the $ character. The main issue here is the context sensitivity; bashrs needs to distinguish between shell scripts and Makefiles.

Issue 3: Awk Regex False Positives

Makefiles frequently use awk commands for text processing. awk employs regular expressions, which can sometimes trigger false positives from bashrs. For instance:

help:
	@awk 'BEGIN {FS = ":.*##"} /^[a-zA-Z_-]+:.*?##/ { printf " %-15s %s\n", $1, $2 }' $(MAKEFILE_LIST)

In this example, the regular expression /^[a-zA-Z_-]+:.*?##/ is perfectly valid. It's used to match specific patterns. bashrs flags this with a warning: SC2102: Ranges can only match single chars (to match + literally, use \+). This isn't accurate. The character class [a-zA-Z_-]+ followed by a + quantifier is valid awk syntax. bashrs should improve how it parses awk and sed patterns or consider skipping them altogether to avoid these incorrect warnings.

Issue 4: Redirection Advice

In Makefiles, you often see redirections used in certain patterns, for example, to check if a command is available. bashrs suggests moving the redirection after fi, but this advice is not always applicable in Makefiles.

target:
	@if command -v tool >/dev/null 2>&1; then \
		tool --do-something; \
	fi

bashrs gives an info message: SC2095: Redirections only apply to the condition command, not the if block. Move redirection after 'fi'. While technically correct in some shell script scenarios, this pattern is often intentional in Makefiles (silencing the condition check). A better approach would be to recognize this pattern and perhaps provide this as an informational message with context specific to Makefiles.

Suggestions for Improvement: Making bashrs Better for Makefiles

Let's discuss some improvements that could enhance bashrs when used for Makefile linting. These suggestions aim to reduce false positives and offer more relevant advice.

1. Makefile-Aware Mode: Implement a special mode or auto-detection for Makefile linting. This could understand $ as an escape, ignore keywords in strings, and recognize Makefile-specific patterns. This would be a game-changer.
2. Context-Aware String Analysis: The tool should be smart enough to differentiate between strings and code. Don't flag shell keywords inside quotes. This is critical for reducing noise.
3. Enhanced Awk/Sed Handling: Improve parsing for awk and sed commands, preventing incorrect regex warnings. Or, consider skipping regex checks within these commands to avoid the issue altogether.
4. Exit Code Configuration: Currently, warnings cause the CI to fail. So changing the exit codes to be more flexible would be a big improvement. The current setup is:
   • Exit 0: No issues
   • Exit 1: Warnings only (non-fatal)
   • Exit 2: Errors found (fatal)
     This would be really helpful in CI pipelines.

Conclusion

bashrs is an awesome tool for shell script linting, and with some thoughtful tweaks, it can become even more effective for Makefiles. By improving how it handles Makefile-specific syntax and avoiding false positives, we can make our build processes cleaner and more reliable. Thanks for this great tool; it's a huge help! These suggested improvements would significantly boost its utility in Makefile linting.