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### What does this PR do? This PR adds lldb pretty printing support for `bun.String`, `ZigString` and `WTFStringImpl` so you don't have to click through so many fields to what the actual string value is.
121 lines
3.2 KiB
Markdown
121 lines
3.2 KiB
Markdown
# LLDB Pretty Printers for Bun
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This directory contains LLDB pretty printers for various Bun data structures to improve the debugging experience.
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## Files
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- `bun_pretty_printer.py` - Pretty printers for Bun-specific types (bun.String, WTFStringImpl, ZigString, BabyList, etc.)
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- `lldb_pretty_printers.py` - Pretty printers for Zig language types from the Zig project
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- `lldb_webkit.py` - Pretty printers for WebKit/JavaScriptCore types
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- `init.lldb` - LLDB initialization commands
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## Supported Types
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### bun.String Types
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- `bun.String` (or just `String`) - The main Bun string type
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- `WTFStringImpl` - WebKit string implementation (Latin1/UTF16)
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- `ZigString` - Zig string type (UTF8/Latin1/UTF16 with pointer tagging)
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### Display Format
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The pretty printers show string content directly, with additional metadata:
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```
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# bun.String examples:
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"Hello, World!" [latin1] # Regular ZigString
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"UTF-8 String 🎉" [utf8] # UTF-8 encoded
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"Static content" [latin1 static] # Static string
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"" # Empty string
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<dead> # Dead/invalid string
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# WTFStringImpl examples:
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"WebKit String" # Shows the actual string content
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# ZigString examples:
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"Some text" [utf16 global] # UTF16 globally allocated
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"ASCII text" [latin1] # Latin1 encoded
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```
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## Usage
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### Option 1: Manual Loading
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In your LLDB session:
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```lldb
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command script import /path/to/bun/misctools/lldb/bun_pretty_printer.py
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```
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### Option 2: Add to ~/.lldbinit
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Add the following line to your `~/.lldbinit` file to load automatically:
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```lldb
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command script import /path/to/bun/misctools/lldb/bun_pretty_printer.py
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```
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### Option 3: Use init.lldb
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```lldb
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command source /path/to/bun/misctools/lldb/init.lldb
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```
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## Testing
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To test the pretty printers:
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1. Build a debug version of Bun:
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```bash
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bun bd
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```
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2. Create a test file that uses bun.String types
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3. Debug with LLDB:
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```bash
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lldb ./build/debug/bun-debug
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(lldb) command script import misctools/lldb/bun_pretty_printer.py
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(lldb) breakpoint set --file your_test.zig --line <line_number>
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(lldb) run your_test.zig
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(lldb) frame variable
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```
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## Implementation Details
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### ZigString Pointer Tagging
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ZigString uses pointer tagging in the upper bits:
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- Bit 63: 1 = UTF16, 0 = UTF8/Latin1
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- Bit 62: 1 = Globally allocated (mimalloc)
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- Bit 61: 1 = UTF8 encoding
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The pretty printer automatically detects and handles these tags.
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### WTFStringImpl Encoding
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WTFStringImpl uses flags in `m_hashAndFlags`:
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- Bit 2 (s_hashFlag8BitBuffer): 1 = Latin1, 0 = UTF16
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### bun.String Tag Union
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bun.String is a tagged union with these variants:
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- Dead (0): Invalid/freed string
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- WTFStringImpl (1): WebKit string
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- ZigString (2): Regular Zig string
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- StaticZigString (3): Static/immortal string
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- Empty (4): Empty string ""
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## Troubleshooting
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If the pretty printers don't work:
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1. Verify the Python script loaded:
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```lldb
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(lldb) script print("Python works")
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```
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2. Check if the category is enabled:
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```lldb
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(lldb) type category list
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```
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3. Enable the Bun category manually:
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```lldb
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(lldb) type category enable bun
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```
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4. For debugging the pretty printer itself, check for exceptions:
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- The pretty printers catch all exceptions and return `<error>`
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- Modify the code to print exceptions for debugging |