Plan: Iterative Removal of Deprecated Symbols

This document outlines the iterative process for identifying and removing deprecated symbols from the WebRTC codebase. The goal is to safely retire old APIs that have zero footprint in internal and external downstream projects.

Removal Criteria

A symbol is a candidate for removal only if it meets all of the following:

  1. Zero Usage: No references found in WebRTC internals or downstream projects.
  2. Maturity: The [[deprecated]] tag was added at least 3 months ago.
  3. Batch Size: No more than 10 symbols are processed in a single iteration.

Phase 1: Candidate Identification (Iterative)

Perform the following steps to generate a list of exactly 10 candidates for the current removal cycle:

  1. Discovery: Search the entire WebRTC codebase (excluding third_party/) for the [[deprecated]] attribute.
  2. Age Verification: Use git blame on the identified lines. Discard any symbols where the deprecation tag was added less than 3 months ago.
  3. Internal Audit: Run git grep <SymbolName> in the WebRTC repository. Discard any symbols that still have internal call-sites (these must be migrated first). Discard the oldest symbols first.
  4. Downstream Audit (CodeSearch): For each matured symbol, perform broad searches in downstream projects (outside third_party/webrtc).
    • External Usage: cs "content:<SymbolName> -file:stable/webrtc"
    • Search Optimization: To minimize false positives with common names (like kPlanB or local_ssrc), prioritize searching for qualified usage (e.g., cs "content:SdpSemantics::kPlanB" or cs "content:::kPlanB") or structural access (e.g., cs "content:.local_ssrc") before performing broad searches for the bare symbol name.
    • Note: Pay special attention to virtual methods. If a symbol is overridden in a downstream project, removing it from the WebRTC base class will break the downstream build.
  5. Iteration Stop: Continue the audit process until exactly 10 symbols have been confirmed to have zero results. Once 10 are found, stop the search.
  6. Documentation: List the 10 selected symbols, their locations, and their modern equivalents.

Phase 2: Execution and Validation

For the 10 selected candidates:

  1. Test Migration: Update any internal WebRTC unit tests or regression tests that still use the deprecated symbol.
  2. Code Removal: Delete the deprecated declarations and implementation.
  3. Bug Tracking: If a TODO with a bug number was attached to the deprecated function and removed, add that bug number with a webrtc: prefix to the Bug: line in the commit message.
  4. Local Build: Perform a clean build of all major targets (e.g., rtc_unittests, rtc_pc_unittests, peerconnection_unittests).
  5. Verification: Run the relevant test suites and ensure 100% pass rate.
  6. Gerrit Upload: Submit the changes for review. The CL description should refer to “downstream projects” generally and MUST NOT contain the specific names of these projects.

Phase 3: High-Usage Coordination

Symbols that return non-zero usage in downstream projects must not be removed using this process. Instead:

  1. Identify the owner of the consuming code.
  2. File a bug against the consuming team referencing the WebRTC deprecation.
  3. Wait for the consuming team to migrate before moving the symbol to Phase 1 in a future iteration.