Skip to content

Commit aee1fad

Browse files
fglockfglock
committed
Add strategy enhancements for debugging sessions
Enhanced the high-yield test analysis strategy with: 1. Technique 20: Preserving test files in dev/sandbox between sessions - Guidelines for using dev/sandbox directory - Cleanup checklist for continuation prompts - Prevents accumulation of temporary files 2. Flexibility Rule for time management - Allow upgrading problem complexity when valuable - Easy→Medium or Medium→Hard when high impact discovered - Prevents abandoning valuable fixes due to rigid limits 3. Created continuation prompt for readonly undef chop issue - Documented 45 minutes of investigation - Preserved test cases in dev/sandbox - Ready for future implementation This session demonstrated effective use of time management strategy, creating a continuation prompt at the 45-minute checkpoint when the issue proved more complex than initially expected.
1 parent a442554 commit aee1fad

File tree

2 files changed

+175
-0
lines changed

2 files changed

+175
-0
lines changed

‎dev/prompts/fix-readonly-undef-chop.md‎

Lines changed: 115 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,115 @@
1+
# Fix Read-Only Undef in Chop Operations
2+
3+
## Objective
4+
Fix the "Modification of a read-only value attempted" error when using chop on `+()` (unary plus on empty list), which currently crashes op/chop.t at line 245.
5+
6+
## Problem Statement
7+
When `chop(+())` is executed, PerlOnJava throws a read-only modification error, but standard Perl allows this operation. This causes op/chop.t to crash at test 138.
8+
9+
## Current Status
10+
- **Test file:** t/op/chop.t
11+
- **Crash at:** line 245 (`map chop(+()), ('')x68;`)
12+
- **Error:** "Modification of a read-only value attempted"
13+
- **Impact:** Test suite crashes, unable to run remaining tests
14+
15+
## Root Cause Analysis
16+
17+
### Investigation Done (45 minutes)
18+
1. Used `--disassemble` to trace bytecode generation
19+
2. Found that `+()` generates: `INVOKESTATIC org/perlonjava/operators/Operator.undef()`
20+
3. `Operator.undef()` returns `scalarUndef`, a cached read-only value
21+
4. Also found `RuntimeList.scalar()` returns `scalarUndef` for empty lists
22+
23+
### Current Implementation
24+
```java
25+
// In Operator.java
26+
public static RuntimeScalar undef() {
27+
return scalarUndef; // Returns cached read-only value
28+
}
29+
30+
// In RuntimeList.java
31+
public RuntimeScalar scalar() {
32+
if (isEmpty()) {
33+
return scalarUndef; // Returns cached read-only value
34+
}
35+
return elements.getLast().scalar();
36+
}
37+
```
38+
39+
### Attempted Fixes That Failed
40+
1. **Changed Operator.undef() to return new RuntimeScalar()** - Still fails
41+
2. **Changed RuntimeList.scalar() to return new RuntimeScalar()** - Still fails
42+
3. **Created undefLvalue() method** - Couldn't identify where to use it
43+
44+
### The Real Issue
45+
The problem appears to be in how `addToScalar()` works. When `+()` is evaluated:
46+
1. It calls `Operator.undef()` to get an initial value
47+
2. Then calls `addToScalar()` on that value
48+
3. But somewhere in this chain, a read-only value is being created or preserved
49+
50+
## Proposed Solutions
51+
52+
### Option 1: Track Lvalue Context
53+
Modify the code generation to detect when undef is needed in an lvalue context (like as an argument to chop) and use a different method.
54+
55+
### Option 2: Make All Undefs Modifiable
56+
Always return modifiable undefs, accepting the performance cost. This is simpler but may have memory implications.
57+
58+
### Option 3: Fix addToScalar Chain
59+
Investigate the full chain of `addToScalar()` calls to find where the read-only value is introduced.
60+
61+
## Test Cases to Verify
62+
63+
```perl
64+
# Minimal test case
65+
chop(+()); # Should not error
66+
67+
# From op/chop.t line 245
68+
map chop(+()), ('')x68; # Should not error
69+
70+
# Comparison
71+
chop(undef); # Should error (literal undef is read-only)
72+
my $x; chop($x); # Should work (variable undef is modifiable)
73+
```
74+
75+
## Implementation Checklist
76+
- [ ] Identify exact code path from `+()` to chop
77+
- [ ] Determine where read-only flag is set
78+
- [ ] Implement fix to return modifiable undef in this context
79+
- [ ] Test with op/chop.t
80+
- [ ] Verify no regressions in other tests
81+
82+
## Expected Impact
83+
- **Direct fix:** 1 crash in op/chop.t
84+
- **Indirect benefit:** Tests 138-148 can run (currently blocked by crash)
85+
- **Potential issues:** May affect performance if all undefs become modifiable
86+
87+
## Complexity Assessment
88+
- **Estimated effort:** 1-2 hours (complex interaction between multiple systems)
89+
- **Risk level:** Medium (affects core scalar operations)
90+
- **Files involved:**
91+
- Operator.java
92+
- RuntimeList.java
93+
- RuntimeScalar.java
94+
- Possibly EmitOperator.java
95+
96+
## Next Steps
97+
1. Trace the exact execution path with debugger
98+
2. Identify where RuntimeScalarReadOnly is introduced
99+
3. Implement targeted fix for this specific case
100+
4. Consider broader implications for other similar operations
101+
102+
## Test Files Preserved
103+
- `dev/sandbox/readonly_undef_chop_test.pl` - Test cases for the issue
104+
105+
## Cleanup Checklist
106+
- [ ] Remove `dev/sandbox/readonly_undef_*.pl` test files after fix
107+
- [ ] Revert changes to `Operator.java` and `RuntimeList.java` if not working
108+
- [ ] Clean up any `test_*.pl` files in project root
109+
- [ ] Move useful test cases to `src/test/resources/` if fix is successful
110+
111+
## Code References
112+
- Bytecode generation: `EmitOperator.emitUndef()`
113+
- Operator implementation: `Operator.undef()`
114+
- List scalar conversion: `RuntimeList.scalar()`
115+
- Scalar assignment: `RuntimeList.addToScalar()`

‎dev/prompts/high-yield-test-analysis-strategy.md‎

Lines changed: 60 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -65,6 +65,36 @@ Time Spent | Root Cause Found | Fix Complexity | Action
6565
> 90 min | Any | Any | STOP - Create prompt
6666
```
6767

68+
**Flexibility Rule: Upgrading Problem Complexity**
69+
70+
If you're working on an **Easy** or **Medium** problem and discover:
71+
- The fix would have high impact (many tests fixed)
72+
- You're close to a solution but need more time
73+
- The learning value is significant
74+
75+
**You can upgrade the complexity classification:**
76+
```
77+
Easy (15-30 min) → Medium (30-60 min)
78+
Medium (30-60 min) → Hard (60-90 min)
79+
```
80+
81+
**When to upgrade:**
82+
- At the checkpoint, you understand the problem well
83+
- The fix affects more tests than initially estimated
84+
- You've found the root cause but implementation is complex
85+
- The issue reveals a systematic problem worth fixing
86+
87+
**Example:**
88+
```
89+
Started: Easy problem (15 min budget)
90+
At 15 min: Found it affects 20 tests, not just 1
91+
Decision: Upgrade to Medium, continue for 30 more minutes
92+
At 45 min: Have working fix, just needs testing
93+
Decision: Complete the fix (worth the time investment)
94+
```
95+
96+
This flexibility prevents abandoning valuable fixes due to rigid time limits while still maintaining discipline.
97+
6898
## Quick Start: Finding High-Yield Targets
6999

70100
### Step 1: Use Automated Analysis Tools
@@ -782,6 +812,36 @@ Minimal reproductions and how to test the fix.
782812
### Temporary Debug Tests
783813
For quick debugging (files in project root), simple scripts without Test::More are fine. These should be cleaned up after use.
784814

815+
### Technique 20: Preserving Test Files Between Sessions
816+
**IMPORTANT:** If you need to preserve test files for continuation in another session:
817+
818+
```bash
819+
# Save important test files to dev/sandbox
820+
mv test_*.pl dev/sandbox/
821+
cp important_test.pl dev/sandbox/issue_name_test.pl
822+
823+
# Document in the continuation prompt
824+
echo "Test files saved in dev/sandbox/:
825+
- issue_name_test.pl - reproduces the bug
826+
- debug_output.txt - contains diagnostic output" >> dev/prompts/fix-issue.md
827+
```
828+
829+
**Best Practice:**
830+
1. Use `dev/sandbox/` directory for files that need to persist
831+
2. Name files descriptively: `issue_readonly_undef_test.pl`
832+
3. **Add to continuation prompt:** "Clean up dev/sandbox/issue_* files after fix"
833+
4. Don't commit sandbox files unless they become permanent tests
834+
835+
**Example in continuation prompt:**
836+
```markdown
837+
## Cleanup Checklist
838+
- [ ] Remove dev/sandbox/readonly_undef_*.pl test files
839+
- [ ] Move useful tests to src/test/resources/ if needed
840+
- [ ] Clear any debug output files in dev/sandbox/
841+
```
842+
843+
This prevents accumulation of temporary files while preserving important debugging context.
844+
785845
## Common PerlOnJava Patterns
786846

787847
### Pattern 1: Context Parameters

0 commit comments

Comments
 (0)