refactor(pest)!: greatly simplified grammar, removed expensive look-ahead that offer no real benefit

[lalvarezt]

This PR simplifies the template parser by removing expensive lookahead operations and consolidating multiple context-specific argument parsers into a single, unified approach.

The Problem

The previous grammar implementation attempted to be "smart" by using context-specific parsing rules:

• simple_arg for basic operations (append, prepend, join)
• regex_arg for regex patterns
• split_arg for split separators
• map_regex_arg for regex within map operations

Each parser had different lookahead logic to determine when special characters (|, :, {, }) should be treated as literals versus syntax. This required extensive operation_keyword lookahead and complex negative assertions like:

split_content = { !(":" ~ (number | range_part)) ~ !("|" ~ operation_keyword) ~ !("}" ~ EOI) ~ ANY }

The Solution

The refactor introduces a single unified argument parser:

argument     = { (escaped_char | normal_char)* }
normal_char  = { !("|" | "}" | "{" | ":" | "\\") ~ ANY }
escaped_char = { "\\" ~ ANY }

All operations now use the same escaping rules. Special characters require explicit escaping - no exceptions, no context-dependent behavior.

Why This is Better

Performance: Lookahead operations are expensive. Removing them provides immediate parsing performance improvements, especially for complex templates.

Maintainability: One set of rules to understand, test, and maintain instead of four context-specific parsers.

Predictability: Users now have clear, consistent rules. If a character is special (|, :, {, }, \), escape it. No need to understand parser internals or memorize context-specific exceptions.

Explicitness: Templates become more intentional. Compare:

{split:|:0}           # old: relies on smart parsing
{split:\|:0}          # new: explicit intent

The second version clearly shows what's a separator and what's syntax.

Robustness: Fewer edge cases means fewer bugs. Complex lookahead logic often fails in corner cases that are hard to predict.

The Trade-off

This is a breaking change. Templates that previously relied on smart escaping need updates:

• Pipes in split separators: {split:|:0} → {split:\|:0}
• Colons in regex patterns: {regex_extract:Version: (\d+):1} → {regex_extract:Version\: (\d+):1}

However, the migration path is straightforward, and the long-term benefits of a simpler, faster, more predictable parser far outweigh the one-time update cost.

[lalvarezt]

/bench d264124 a194856

[github-actions]

🚀 Benchmark comparison started

Comparing:

• Baseline: d2641242c4628bc725ea5fa0602db1f5a51d8f9d
• Current: a194856553402e5645376917e43726d816a3b581

Parameters:

• Iterations: 100
• Sizes: 1000,5000,10000

Results will be posted here when complete...

[github-actions]

🔬 Benchmark Comparison Report

Requested by: @lalvarezt

Comparison:

• Baseline (older): d2641242c4628bc725ea5fa0602db1f5a51d8f9d (d264124)
• Current (newer): a194856553402e5645376917e43726d816a3b581 (a194856)

Parameters:

• Iterations: 100
• Sizes: 1000,5000,10000

---

📊 Benchmark Comparison Report

Input Size: 10,000 paths

Baseline Timestamp: 1762543388
Current Timestamp: 1762543498

Performance Comparison

Template	Avg/Path	Change	p95	Change	Throughput	Change
Basename no ext	1.22μs	➖ -1.3%	1.26μs	➖ -0.4%	817.14K/s	➖ +1.3%
Breadcrumb last 3	1.57μs	➖ -0.3%	1.61μs	➖ +0.6%	635.35K/s	➖ +0.2%
Chain: map complex	3.22μs	🟢 -52.0%	3.29μs	🟢 -52.5%	310.78K/s	🟢 +108.2%
Chain: split+filter+sort+join	5.73μs	➖ -1.2%	5.77μs	➖ -1.4%	174.46K/s	➖ +1.2%
Chain: trim+upper+pad	1.39μs	➖ +0.8%	1.42μs	➖ +0.7%	718.51K/s	➖ -0.8%
Extract directory	1.35μs	➖ +0.7%	1.37μs	➖ +0.3%	739.97K/s	➖ -0.7%
Extract filename	375ns	🟡 +4.2%	396ns	⚠️ +5.3%	2.67M/s	🟡 -4.0%
File extension	1.23μs	➖ -1.7%	1.28μs	🟢 -6.8%	812.71K/s	➖ +1.7%
Filter	5.27μs	➖ +0.5%	5.32μs	➖ +0.2%	189.64K/s	➖ -0.5%
Join	1.34μs	➖ -0.8%	1.36μs	✅ -2.9%	748.21K/s	➖ +0.8%
Lower	940ns	🟡 +3.6%	1.00μs	⚠️ +6.8%	1.06M/s	🟡 -3.5%
Normalize filename	1.07μs	✅ -2.3%	1.10μs	➖ -1.3%	930.86K/s	✅ +2.3%
Pad	1.20μs	➖ +1.6%	1.23μs	🟡 +2.4%	830.72K/s	➖ -1.6%
Regex extract filename	4.86μs	➖ -0.9%	4.91μs	✅ -3.6%	205.86K/s	➖ +0.9%
Remove hidden dirs	5.03μs	➖ +1.4%	5.07μs	➖ +0.7%	198.98K/s	➖ -1.4%
Replace complex	3.45μs	➖ +0.6%	3.51μs	➖ +1.7%	289.94K/s	➖ -0.6%
Replace simple	3.59μs	➖ -0.9%	3.65μs	➖ -1.5%	278.30K/s	➖ +0.9%
Reverse	920ns	➖ +0.4%	949ns	➖ +1.0%	1.09M/s	➖ -0.4%
Slug generation	493ns	🟢 -45.9%	506ns	🟢 -45.7%	2.03M/s	🟢 +84.7%
Sort	1.75μs	➖ +1.3%	1.77μs	➖ +0.9%	571.43K/s	➖ -1.3%
Split all	540ns	✅ -4.9%	563ns	🟢 -5.5%	1.85M/s	🟢 +5.2%
Split last index	353ns	🟢 -8.5%	367ns	🟢 -10.9%	2.83M/s	🟢 +9.4%
Strip ANSI	276ns	✅ -2.8%	279ns	🟢 -7.3%	3.62M/s	✅ +3.1%
Substring	1.11μs	➖ -0.2%	1.16μs	➖ +0.8%	898.03K/s	➖ +0.2%
Trim	1.04μs	➖ -0.1%	1.09μs	🟡 +2.2%	964.47K/s	➖ +0.1%
Unique	2.25μs	➖ -0.7%	2.28μs	➖ -0.4%	443.45K/s	➖ +0.7%
Upper	892ns	➖ -0.7%	920ns	➖ -1.0%	1.12M/s	➖ +0.7%
Uppercase all components	2.42μs	🟡 +2.0%	2.81μs	🔴 +17.4%	413.49K/s	➖ -2.0%

Summary

• Total templates compared: 28
• Improvements: 3 🟢
• Regressions: 0 🔴
• Neutral: 25 ➖

✨ Performance Improvements

• Chain: map complex: 52.0% faster
• Slug generation: 45.9% faster
• Split last index: 8.5% faster

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Legend

• 🟢 Significant improvement (>5% faster)
• ✅ Improvement (2-5% faster)
• ➖ Neutral (<2% change)
• 🟡 Caution (2-5% slower)
• ⚠️ Warning (5-10% slower)
• 🔴 Regression (>10% slower)

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_{Triggered by /bench command}