Consolidate Error Sections by Resolution Theme

Replace individual diagnostic H2 sections with thematic H2 sections organized around shared resolution strategies.

Required Input

Collect the destination filename for the consolidated .md file in docs/csharp/language-reference/compiler-messages/.

Key Paths

• Destination: docs/csharp/language-reference/compiler-messages/{destination-filename}
• Reference examples: Other *-errors.md files in docs/csharp/language-reference/compiler-messages/

Phase A: Propose Themes

1. Read the destination and identify every error code and current H2 section.
2. Read two or three other consolidated *-errors.md files to learn the expected structure and tone.
3. Group codes by their messages, underlying language rules, and shared resolution strategies. Each theme must represent a coherent set of related diagnostics.
4. For each proposed theme, provide:
   • The title that would become its H2 heading and anchor.
   • The included error codes.
   • A one-sentence rationale.

Present the proposal and stop:

### Proposed themes

1. **Operator signature requirements** (`#operator-signature-requirements`)
   - CS0448, CS0559, CS0562, CS0563, CS0564, CS0567, CS0590
   - These errors all relate to invalid parameter or return types in operator declarations.

2. **Overflow and underflow errors** (`#overflow-and-underflow-errors`)
   - CS0031, CS0220, CS0221, CS0463, CS0543, CS0594, CS0652, CS1021, CS8778, CS8973
   - These errors all involve constant values or operations that exceed type boundaries.

Tell the user:

Review and approve each theme. Let me know which to proceed with and any adjustments.

Wait for user approval before proceeding to Phase B.

Phase B: Build Approved Thematic Sections

For each approved theme, complete the following steps.

1. Update the Master Error List

Link each code to its theme anchor and keep the complete list in numeric order:

- [**CS{NNNN}**](#{theme-anchor}): *{verbatim compiler error message}*

2. Create the Thematic H2

Replace the theme's individual diagnostic H2 sections with one section:

## {Theme title}

- **CS{NNNN}**: *{verbatim error message}*
- **CS{NNNN}**: *{verbatim error message}*

{Resolution-focused content}

Repeat codes and messages without anchor links inside the thematic section.

3. Write Resolution-Focused Content

• Focus on correcting each diagnostic rather than teaching the full language feature.

• Link to the language reference and relevant C# specification sections that explain the enforced rules. Use repository-consistent links.

• State what to change and why in complete, direct, action-oriented sentences. Identify affected codes in bold parentheses. Keep the guidance concise while retaining the source requirement to explain the correction fully. For example:

  Change the return type of ++ or -- operators to the containing type or a type derived from it (CS0448). The language requires that increment and decrement operators return a value compatible with the containing type so the result can be assigned back to the same variable.

• Remove lengthy examples. Brief inline code is acceptable.

• Do not add H3 headings; keep each thematic section flat under its H2.

• Explicitly identify diagnostics that the latest C# compiler no longer produces.

• Reuse source text or a brief source example when it supports the resolution.

4. Remove Absorbed H2 Sections

Delete every individual ## CS{NNNN} section absorbed into the theme.

Final Checks

After building all approved themes:

1. Verify the master list is in numeric order.
2. Verify every front matter code appears in the master list.
3. Verify every master-list code links to an existing thematic anchor.
4. Verify no individual diagnostic H2 section remains orphaned.