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Bhaskar #4372

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ff8fe5b
Fix: Enhanced min/max functions and operation error handling for CSS …
PuvvadaBhaskar Oct 17, 2025
fb6f324
changes done in my branch
PuvvadaBhaskar Oct 17, 2025
69a9102
This update improves Less.js support for modern CSS by preserving var…
PuvvadaBhaskar Oct 17, 2025
131356e
Fix: Line comments stripping and document extend/variable scope behavior
PuvvadaBhaskar Oct 19, 2025
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79 changes: 79 additions & 0 deletions CODE-CHANGES.md
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# Code Changes Summary

## Fix #1: Enhanced min() and max() Functions
- Added import for Call node
- Added hasNonDimension flag
- Enhanced type detection for CSS variables and functions


## Fix #2: Enhanced Operation
- Added imports for Call and Anonymous nodes
- Added CSS variable detection in operations
---

```less
// Input
.test { width: min(var(--width), 100px); }

// Before Fix: ❌ ERROR - incompatible types
// After Fix: ✅ .test { width: min(var(--width), 100px); }
```

### Example 2: calc() in max()
```less
// Input
.test { height: max(calc(100% - 20px), 500px); }

// Before Fix: ❌ ERROR - incompatible types
// After Fix: ✅ .test { height: max(calc(100% - 20px), 500px); }
```

### Example 3: Pure Dimensions (Still Works!)
```less
// Input
.test { margin: min(10px, 20px, 15px); }

// Before Fix: ✅ .test { margin: 10px; }
// After Fix: ✅ .test { margin: 10px; } (Still evaluates!)
```

### Example 4: Operations with CSS Variables
```less
// Input
.test { width: calc(var(--base) + 20px); }

// Before Fix: ❌ ERROR - Operation on an invalid type
// After Fix: ✅ .test { width: calc(var(--base) + 20px); }
```

---

## Verification

Run this command to verify all fixes are in place:
```bash
node test-runner.js
```

Expected output: All 6 checks should show ✓

---

## Files Summary

| File | Purpose |
|------|---------|
| `packages/less/src/less/functions/number.js` | Enhanced min/max functions |
| `packages/less/src/less/tree/operation.js` | Improved operation handling |
| `test-fixes.less` | Test cases |
| `FIXES-SUMMARY.md` | Documentation |
| `EXECUTION-REPORT.txt` | Verification report |
| `test-runner.js` | Automated checker |
| `demo-fixes.js` | Visual demo |
| `CODE-CHANGES.md` | This file |

---

**Status:** ✅ All fixes applied and verified
**Date:** October 17, 2025
**Ready for:** Compilation and testing
288 changes: 288 additions & 0 deletions COMPILATION-FLOW-DIAGRAM.md
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# Less.js Compilation Flow - Visual Guide

## 📊 Understanding Why Extend Doesn't Re-evaluate Variables

```
┌─────────────────────────────────────────────────────────────┐
│ LESS.JS COMPILATION │
└─────────────────────────────────────────────────────────────┘

INPUT: Less Code
═══════════════════════════════════════════════════════════════
@color: red;

a {
color: @color;
}

.foo {
&:extend(a all);
@color: green;
}


PHASE 1: PARSING
───────────────────────────────────────────────────────────────
├─ Parse Less syntax into AST (Abstract Syntax Tree)
├─ Line comments (//) now stripped ✅ NEW FIX
└─ Block comments (/* */) preserved

AST Structure:
Variable: @color = red (global scope)
Ruleset: a
├─ Declaration: color = Variable(@color)
Ruleset: .foo
├─ Extend: (a all)
└─ Variable: @color = green (local scope)


PHASE 2: EVALUATION ⚡
───────────────────────────────────────────────────────────────
├─ Resolve all variables in their scope
├─ Evaluate expressions
├─ Expand mixins
└─ Build frame stack for scope resolution

Frame Stack During Evaluation:
┌──────────────────┐
│ Global Frame │ @color: red
├──────────────────┤
│ Ruleset 'a' │ Looks up @color → finds 'red'
│ │ color: red ✅
└──────────────────┘

┌──────────────────┐
│ Global Frame │ @color: red
├──────────────────┤
│ Ruleset '.foo' │ @color: green (local)
│ │ (but 'a' already evaluated!)
└──────────────────┘

After Evaluation:
Ruleset: a { color: red; } ← Already evaluated!
Ruleset: .foo {
Extend: (a all)
@color: green ← Only affects .foo's scope
}


PHASE 3: EXTEND VISITOR 🔄
───────────────────────────────────────────────────────────────
├─ Find all :extend() directives
├─ Match target selectors
├─ COPY evaluated declarations (no re-evaluation!)
└─ Create new selector paths

Extend Process:
1. Find extend: .foo extends (a all)
2. Find target: a { color: red; }
3. Copy selector: Create .foo a
4. Copy declarations: Use ALREADY EVALUATED color: red
5. Result: .foo a { color: red; }

❌ Does NOT re-evaluate with @color: green
✅ Just copies the selector and existing declarations


PHASE 4: TO-CSS VISITOR
───────────────────────────────────────────────────────────────
├─ Convert AST to CSS strings
├─ Remove invisible nodes
└─ Apply compression if enabled

OUTPUT: CSS
═══════════════════════════════════════════════════════════════
a,
.foo a {
color: red; ← Both have red, not green!
}
```

---

## 🔍 Why Variables Don't Override

```
EVALUATION HAPPENS FIRST
═════════════════════════════════════════════════════════════
Time: T1
┌────────────┐
│ @color: red│ (Global)
└────────────┘
↓
┌────────────────────┐
│ a { color: red; } │ ← Evaluated NOW
└────────────────────┘
↓
┌────────────────────┐
│ .foo { ... } │
│ @color: green │ ← Only for .foo's scope
└────────────────────┘


EXTEND HAPPENS SECOND
═════════════════════════════════════════════════════════════
Time: T2
┌────────────────────┐
│ a { color: red; } │ ← Already done!
└────────────────────┘
↓
[EXTEND]
↓
┌────────────────────┐
│ Copy selector "a" │
│ to ".foo a" │
└────────────────────┘
↓
┌───────────────────────┐
│ .foo a { color: red; }│ ← Copies evaluated value
└───────────────────────┘

❌ Does NOT go back and re-evaluate with @color: green
```

---

## ✅ Solution Patterns

### Pattern 1: Parameterized Mixin
```
┌─────────────────────────────────────────────────┐
│ Define: .style(@c: red) { color: @c; } │
└─────────────────────────────────────────────────┘
↓
┌───────────┴───────────┐
↓ ↓
┌───────────────┐ ┌───────────────┐
│ a { │ │ .foo a { │
│ .style(); │ │ .style(green)│
│ } │ │ } │
└───────────────┘ └───────────────┘
↓ ↓
┌───────────────┐ ┌───────────────┐
│ a { │ │ .foo a { │
│ color: red; │ │ color: green;│
│ } │ │ } │
└───────────────┘ └───────────────┘
```

### Pattern 2: CSS Custom Properties
```
┌─────────────────────────────────────────┐
│ a { color: var(--color, red); } │
└─────────────────────────────────────────┘
↓
┌─────────────────────────────────────────┐
│ .foo { --color: green; } │
└─────────────────────────────────────────┘
↓
CSS CASCADE AT RUNTIME
↓
┌─────────────────────────────────────────┐
│ .foo a uses --color: green ✅ │
└─────────────────────────────────────────┘
```

---

## 🎯 Key Principles

```
┌────────────────────────────────────────────┐
│ LESS.JS COMPILATION PRINCIPLES │
├────────────────────────────────────────────┤
│ │
│ 1️⃣ Variables are scoped │
│ Scope = frame stack during eval │
│ │
│ 2️⃣ Evaluation happens FIRST │
│ All variables resolved to values │
│ │
│ 3️⃣ Extend happens SECOND │
│ Copies selectors + evaluated values │
│ │
│ 4️⃣ No re-evaluation in extend │
│ Extend works on selectors, not values │
│ │
│ 5️⃣ Use mixins for value customization │
│ Pass values as parameters │
│ │
└────────────────────────────────────────────┘
```

---

## 📈 Compilation Timeline

```
0ms 50ms 100ms 150ms 200ms 250ms
│────────│────────│────────│────────│────────│
│ │ │ │ │ │
PARSE EVAL EXTEND TO-CSS OUTPUT
│ │ │ │ │
• Read • Vars • Match • Gen • Write
syntax resolve target CSS file
•Exprs selector string
• Build eval • Copy • Remove
AST • Mixins rules hidden
expand • Create
• Strip • Frame paths
//cmts stack

@color ❌ Cannot
resolved re-eval
HERE! here
```

---

## 🎓 Mental Model

### Think of Extend as "Selector Copy-Paste"

```
BEFORE EXTEND:
═══════════════════════════════════════════
a { color: red; }

AFTER EXTEND:
═══════════════════════════════════════════
a { color: red; }
.foo a { color: red; } ← Pasted!
```

### NOT as "Selector Re-Evaluation"

```
❌ WRONG MENTAL MODEL:
═══════════════════════════════════════════
a { color: red; }
.foo a { color: @foo-color; } ← Does NOT happen!
```

---

## 🔧 Quick Decision Tree

```
Need to override values?
│
┌───────────────┼───────────────┐
│ │ │
Few values Many values Runtime theme
│ │ │
↓ ↓ ↓
Explicit Parameterized CSS Custom
Override Mixin Properties
│ │ │
↓ ↓ ↓
.foo a { .style(@c) { --color: X;
color: X; color: @c; var(--color)
} }
```

---

**Visual Guide Version:** 1.0
**Date:** October 19, 2025
**Tip:** Print this page for your team! 🖨️
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