Fix DateTime test failures: overload warnings and custom warning categories

dev/architecture/README.md

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+# PerlOnJava Architecture Overview
+
+This directory contains architecture documentation for the PerlOnJava compiler and runtime.
+
+## Quick Overview
+
+PerlOnJava is a Perl 5 implementation that compiles Perl source code to JVM bytecode. The system consists of:
+
+1. **Frontend** (`org.perlonjava.frontend`)
+   - Lexer: Tokenizes Perl source code
+   - Parser: Builds Abstract Syntax Tree (AST)
+   - Semantic analysis: Variable resolution, scope handling
+
+2. **Backend** (`org.perlonjava.backend`)
+   - JVM backend: Emits JVM bytecode using ASM library
+   - Bytecode interpreter: Interprets a subset of operations for eval STRING
+
+3. **Runtime** (`org.perlonjava.runtime`)
+   - Runtime types: RuntimeScalar, RuntimeArray, RuntimeHash, RuntimeCode
+   - Operators: Arithmetic, string, comparison, I/O
+   - Perl modules: Built-in implementations of core modules
+
+## Key Architecture Documents
+
+| Document | Description |
+|----------|-------------|
+| [dynamic-scope.md](dynamic-scope.md) | Dynamic scoping via `local` and DynamicVariableManager |
+| [lexical-pragmas.md](lexical-pragmas.md) | Lexical warnings, strict, and features |
+| [../design/interpreter.md](../design/interpreter.md) | Bytecode interpreter design |
+| [../design/variables_and_values.md](../design/variables_and_values.md) | Runtime value representation |
+
+## Compilation Pipeline
+
+```
+Perl Source
+    │
+    ▼
+┌─────────┐
+│  Lexer  │  Tokenizes source into LexerTokens
+└────┬────┘
+     │
+     ▼
+┌─────────┐
+│ Parser  │  Builds AST (AbstractNode tree)
+└────┬────┘
+     │
+     ▼
+┌─────────────┐
+│  Visitors   │  Analysis passes (variable resolution, etc.)
+└─────┬───────┘
+      │
+      ▼
+┌───────────────┐
+│ JVM Emitter   │  Generates bytecode via ASM
+└───────┬───────┘
+        │
+        ▼
+   JVM Bytecode
+```
+
+## Runtime Architecture
+
+```
+┌────────────────────────────────────────────────┐
+│                  Perl Code                     │
+└────────────────────────────────────────────────┘
+                      │
+                      ▼
+┌────────────────────────────────────────────────┐
+│              Runtime Types                      │
+│  RuntimeScalar, RuntimeArray, RuntimeHash      │
+│  RuntimeCode, RuntimeGlob, RuntimeIO           │
+└────────────────────────────────────────────────┘
+                      │
+                      ▼
+┌────────────────────────────────────────────────┐
+│              Global State                       │
+│  GlobalVariable (package variables)            │
+│  DynamicVariableManager (local scoping)        │
+│  CallerStack (call frame tracking)             │
+└────────────────────────────────────────────────┘
+                      │
+                      ▼
+┌────────────────────────────────────────────────┐
+│                   JVM                          │
+└────────────────────────────────────────────────┘
+```
+
+## Key Design Decisions
+
+1. **Direct JVM Bytecode**: We emit bytecode directly rather than generating Java source, enabling better optimization and avoiding Java language limitations.
+
+2. **Dual Backend**: JVM bytecode for compiled code, bytecode interpreter for `eval STRING` to avoid runtime class generation overhead.
+
+3. **Dynamic Scoping**: Implemented via `DynamicVariableManager` which maintains a stack of saved values, restored on scope exit.
+
+4. **Lexical Pragmas**: Warnings and strict are tracked in the symbol table at compile time and propagate via `CompilerFlagNode`.
+
+## See Also
+
+- [AGENTS.md](../../AGENTS.md) - Development guidelines
+- [dev/design/](../design/) - Detailed design documents

dev/architecture/dynamic-scope.md

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+# Dynamic Scoping in PerlOnJava
+
+This document explains how PerlOnJava implements Perl's dynamic scoping via the `local` keyword and how the same mechanism is used for other features.
+
+## Overview
+
+Perl's `local` keyword provides dynamic scoping: it temporarily saves a variable's value and restores it when the current scope exits. This is different from lexical scoping (`my`), which creates a new variable visible only in the current block.
+
+```perl
+$x = "global";
+sub foo {
+    local $x = "local";
+    bar();  # sees $x = "local"
+}
+sub bar {
+    print $x;  # prints "local" when called from foo()
+}
+foo();
+print $x;  # prints "global"
+```
+
+## Implementation
+
+### Core Components
+
+#### 1. DynamicState Interface
+
+All values that can be dynamically scoped implement `DynamicState`:
+
+```java
+public interface DynamicState {
+    void dynamicSaveState();    // Save current state
+    void dynamicRestoreState(); // Restore saved state
+}
+```
+
+Implementations:
+- `RuntimeScalar` - scalar variables
+- `RuntimeArray` - array variables  
+- `RuntimeHash` - hash variables
+- `RuntimeGlob` - typeglobs
+- `DeferBlock` - defer block execution
+- `RegexState` - regex match state ($1, $2, etc.)
+
+#### 2. DynamicVariableManager
+
+Manages a stack of saved states:
+
+```java
+public class DynamicVariableManager {
+    private static final Deque<DynamicState> variableStack = new ArrayDeque<>();
+
+    // Save current state and push onto stack
+    public static void pushLocalVariable(DynamicState variable) {
+        variable.dynamicSaveState();
+        variableStack.addLast(variable);
+    }
+
+    // Restore all states back to a saved level
+    public static void popToLocalLevel(int targetLevel) {
+        while (variableStack.size() > targetLevel) {
+            DynamicState variable = variableStack.removeLast();
+            variable.dynamicRestoreState();
+        }
+    }
+
+    // Get current stack level (saved at block entry)
+    public static int getLocalLevel() {
+        return variableStack.size();
+    }
+}
+```
+
+#### 3. RuntimeScalar State Management
+
+Each `RuntimeScalar` has its own save stack:
+
+```java
+public class RuntimeScalar implements DynamicState {
+    private static final Stack<RuntimeScalar> dynamicStateStack = new Stack<>();
+
+    @Override
+    public void dynamicSaveState() {
+        // Save a copy of current state
+        RuntimeScalar copy = new RuntimeScalar();
+        copy.type = this.type;
+        copy.value = this.value;
+        dynamicStateStack.push(copy);
+    }
+
+    @Override
+    public void dynamicRestoreState() {
+        RuntimeScalar saved = dynamicStateStack.pop();
+        this.type = saved.type;
+        this.value = saved.value;
+    }
+}
+```
+
+### Code Generation
+
+When the compiler sees `local $x`:
+
+1. **Block Entry**: Save current local level
+   ```java
+   int savedLevel = DynamicVariableManager.getLocalLevel();
+   ```
+
+2. **Local Assignment**: Save and modify variable
+   ```java
+   DynamicVariableManager.pushLocalVariable(variable);
+   variable.set(newValue);
+   ```
+
+3. **Block Exit**: Restore all local variables (in finally block)
+   ```java
+   DynamicVariableManager.popToLocalLevel(savedLevel);
+   ```
+
+### Detection of Local Usage
+
+`FindDeclarationVisitor` scans AST blocks to detect if `local` is used:
+
+```java
+public static boolean containsLocalOrDefer(Node blockNode) {
+    FindDeclarationVisitor visitor = new FindDeclarationVisitor();
+    visitor.operatorName = "local";
+    blockNode.accept(visitor);
+    return visitor.containsLocalOperator || visitor.containsDefer;
+}
+```
+
+This allows the compiler to skip local setup/teardown for blocks that don't need it.
+
+## Other Uses of DynamicVariableManager
+
+The same mechanism is used for several other features:
+
+### 1. Defer Blocks
+
+`defer { ... }` blocks execute code when scope exits:
+
+```perl
+{
+    defer { print "cleanup\n" }
+    print "work\n";
+}  # prints: work, cleanup
+```
+
+Implementation:
+```java
+public class DeferBlock implements DynamicState {
+    private final RuntimeCode code;
+
+    @Override
+    public void dynamicRestoreState() {
+        // Execute the defer block
+        code.apply(new RuntimeArray(), RuntimeContextType.VOID);
+    }
+}
+```
+
+### 2. Regex State
+
+Match variables (`$1`, `$2`, `$&`, etc.) are saved/restored:
+
+```java
+public class RegexState implements DynamicState {
+    // Saves: captureGroups, lastMatch, prematch, postmatch, etc.
+}
+```
+
+This ensures regex state is properly scoped in nested matches.
+
+### 3. Warning Scope (${^WARNING_SCOPE})
+
+Runtime warning suppression uses local semantics:
+
+```perl
+{
+    no warnings 'DateTime';  # Sets local ${^WARNING_SCOPE} = scopeId
+    DateTime->new(...);      # warnif() checks ${^WARNING_SCOPE}
+}  # ${^WARNING_SCOPE} restored to 0
+```
+
+The `CompilerFlagNode` emits:
+```java
+GlobalRuntimeScalar.makeLocal("${^WARNING_SCOPE}");
+scopeVar.set(scopeId);
+```
+
+### 4. Signal Handlers
+
+`local $SIG{__WARN__}` and `local $SIG{__DIE__}` use the same mechanism:
+
+```perl
+{
+    local $SIG{__WARN__} = sub { ... };
+    # warnings go to custom handler
+}  # original handler restored
+```
+
+## Exception Safety
+
+`popToLocalLevel()` is exception-safe:
+
+```java
+public static void popToLocalLevel(int targetLevel) {
+    Throwable pendingException = null;
+
+    while (variableStack.size() > targetLevel) {
+        DynamicState variable = variableStack.removeLast();
+        try {
+            variable.dynamicRestoreState();
+        } catch (Throwable t) {
+            // Continue cleanup, remember last exception
+            pendingException = t;
+        }
+    }
+
+    // Re-throw after all cleanup
+    if (pendingException != null) {
+        throw pendingException;
+    }
+}
+```
+
+This ensures:
+1. All local variables are restored even if one throws
+2. Defer blocks all execute even if one throws
+3. The last exception "wins" (Perl semantics)
+
+## Performance Considerations
+
+1. **Stack Allocation**: Uses `ArrayDeque` (no synchronization overhead)
+2. **Lazy Detection**: `containsLocalOrDefer()` avoids setup for blocks without `local`
+3. **Per-Variable Stacks**: Each variable type manages its own save stack
+
+## Files
+
+| File | Purpose |
+|------|---------|
+| `DynamicState.java` | Interface for saveable state |
+| `DynamicVariableManager.java` | Central stack management |
+| `RuntimeScalar.java` | Scalar save/restore |
+| `RuntimeArray.java` | Array save/restore |
+| `RuntimeHash.java` | Hash save/restore |
+| `DeferBlock.java` | Defer block execution |
+| `RegexState.java` | Regex state save/restore |
+| `Local.java` | Code generation helpers |
+| `FindDeclarationVisitor.java` | Detection of local usage |
+
+## See Also
+
+- [lexical-pragmas.md](lexical-pragmas.md) - How warnings/strict use this mechanism
+- [../design/warnings-scope.md](../design/warnings-scope.md) - Warning scope design