feat: Add multi-dimensional array support (fixes #49)

[richardwooding]

Summary

Implements comprehensive support for PostgreSQL multi-dimensional arrays with automatic dimension detection from database schema metadata.

Fixes #49

Changes

Core Implementation

1. Schema Enhancement (pg/provider.go)

   • Added Dimensions int field to FieldSchema struct
   • Implemented detectArrayDimensions() function to parse PostgreSQL type strings
   • Updated LoadTableSchema() to query udt_name column and detect dimensions
   • Handles both bracket notation (integer[][]) and underscore notation (_int4[])
   • Correctly combines notations (e.g., _int4[] = 2D array)

2. SQL Generation (cel2sql.go)

   • Updated getArrayDimension() to use CEL typeMap for accurate type lookup
   • Modified ARRAY_LENGTH generation to use detected dimensions: ARRAY_LENGTH(field, dimension)
   • Supports 1D through 4D+ arrays

Test Coverage

1. Unit Tests (pg/dimension_detection_test.go)

   • 22 test cases for detectArrayDimensions()
   • Covers scalar types, 1D-4D arrays, both notations, edge cases

2. Integration Tests (multidim_array_test.go)

   • Tests 1D, 2D, 3D, and 4D array size() operations
   • Backward compatibility tests (defaults to 1D without schema)
   • Explicit vs implicit dimension specification tests

Dimension Detection Logic

// Examples:
"integer"       → 0 (not an array)
"integer[]"     → 1 (1D array)
"_int4"         → 1 (1D array, underscore notation)
"integer[][]"   → 2 (2D array)
"_int4[]"       → 2 (2D array, underscore + bracket)
"integer[][][]" → 3 (3D array)
"_int4[][]"     → 3 (3D array)

Backward Compatibility

✅ Fully backward compatible

• Arrays without schema information default to dimension 1
• Explicit Dimensions=0 defaults to dimension 1
• Existing code continues to work without changes
• All 238 existing tests pass

Example Usage

With Schema (Automatic Detection)

// Database schema introspection automatically detects dimensions
provider, err := pg.NewTypeProviderWithConnection(ctx, connString)
err = provider.LoadTableSchema(ctx, "products")

env, err := cel.NewEnv(
    cel.CustomTypeProvider(provider),
    cel.Variable("product", cel.ObjectType("products")),
)

// For a 2D array field 'matrix integer[][]':
ast, _ := env.Compile("size(product.matrix) > 0")
sql, _ := cel2sql.Convert(ast, cel2sql.WithSchemas(provider.GetSchemas()))
// Output: COALESCE(ARRAY_LENGTH(product.matrix, 2), 0) > 0

Manual Schema Definition

schema := pg.NewSchema([]pg.FieldSchema{
    {Name: "tags", Type: "text", Repeated: true, Dimensions: 1},      // 1D
    {Name: "matrix", Type: "integer", Repeated: true, Dimensions: 2},  // 2D
    {Name: "cube", Type: "float", Repeated: true, Dimensions: 3},      // 3D
})

Test Results

✓ All 238 tests pass
✓ Coverage: 72.2%
✓ No lint issues
✓ Backward compatibility verified

Related Issues

• Fixes Hardcoded Array Dimension Limits Multi-Dimensional Array Support #49 (Hardcoded Array Dimension Limits Multi-Dimensional Array Support)
• Related to LIKE Pattern Escaping Missing Explicit ESCAPE Clause #40 (LIKE escaping)
• Related to Missing Type Validation for JSON Array Comprehensions #48 (JSON comprehensions)

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