Fix duplicate function generation when indexes target same columns

[imran31415]

Fix duplicate function generation when indexes target same columns

Problem

When a table has multiple indexes targeting the same column(s), dbtpl generates duplicate function names, causing Go compilation errors.

Specific scenario: Tables with both primary keys and unique indexes on the same column generate identical function names:

CREATE TABLE users (
    id SERIAL PRIMARY KEY,
    email VARCHAR(255) NOT NULL
);

-- This creates duplicate function generation:
CREATE UNIQUE INDEX users_id_unique ON users (id);

Result: Two functions with identical signatures:

func UserById(ctx context.Context, db DB, id int) (*User, error) { ... }  // from PK
func UserById(ctx context.Context, db DB, id int) (*User, error) { ... }  // from unique index - DUPLICATE!

Error: UserById redeclared in this block

Solution

This PR implements backwards-compatible duplicate detection and resolution:

1. Conflict Detection: Analyze all indexes for a table to identify naming conflicts
2. Smart Suffixes: Add type-specific suffixes only to conflicting indexes (keeping first/primary unchanged):
   • Primary keys keep original names (backwards compatible)
   • _unique for conflicting unique indexes
   • _idx for conflicting regular indexes
3. True Backwards Compatibility: Existing function names remain unchanged

Results

Before (broken):

func XoTestById(...) { ... }  // from primary key
func XoTestById(...) { ... }  // from unique index - DUPLICATE!

After (fixed):

func XoTestById(...) { ... }       // from primary key (unchanged - backwards compatible)
func XoTestByIdUnique(...) { ... } // from unique index (suffix added to resolve conflict)

Backwards Compatible:

// Single indexes maintain original names - no breaking changes
func UserByEmail(...) { ... }  // still generates same name

Implementation

Test-Driven Development Approach:

1. Added failing test first (TestIndexFuncNameDuplicates):

   • Created test cases that reproduce the duplicate function bug
   • Test initially failed as expected, exposing the issue
   • Added backwards compatibility tests (TestBackwardsCompatibility)

2. Implemented the fix:

   • Modified indexFuncName() to generate base names without automatic suffixes
   • Added assignUniqueIndexFuncNames() for conflict-aware name assignment with priority ordering
   • Primary keys get priority to keep original names (backwards compatible)
   • Updated index processing pipeline to use two-pass approach

3. Verified fix works:

   • All tests now pass, confirming the fix resolves duplicate generation
   • Backwards compatibility tests ensure no breaking changes
   • Generated code compiles successfully without duplicate function errors

Demo

Live demonstration available at: https://github.com/imran31415/dbdpl-demo-fix

Testing

• ✅ Unit tests cover duplicate detection and resolution
• ✅ Backwards compatibility tests ensure no breaking changes
• ✅ Integration tests verify generated code compiles successfully
• ✅ Demo repository provides real-world validation

Fixes #407