migrate-custom-code

Migrate Custom Code

ATC-driven S/4HANA custom code migration assistant with automated fix proposals.

This skill replicates SAP Joule's "Custom Code Migration" capability by combining ARC-1 (SAP system access) with mcp-sap-docs (documentation & best practices). It runs ATC readiness checks, groups and explains findings, and generates replacement code following modern ABAP patterns.

Smart Defaults (apply silently, do NOT ask)

Input

The user provides an object or package to check (e.g., ZCL_SALES_HANDLER, Z_REPORT_POSTING, ZSALES_PKG).

Only the object name is required. If the user provides just an object name, auto-detect the type and proceed with the default variant and fix scope.

Optionally, the user may specify:

• Object type (default: auto-detect via SAPSearch)
• Target release variant (e.g., S4HANA_2023, S4HANA_READINESS; default: system default)
• Scope — explain (findings only) or fix (explain + fix proposals; default: fix)

Step 1: Run ATC Readiness Check

ATC gotchas (verified live on S/4HANA 2023):

• ATC skips $TMP / local objects. A check run against a $TMP object resolves to an empty object set and returns zero findings — this is not "clean code", it's "not checked". Run ATC against objects in a transportable package. If the user points you at $TMP code, say so and ask them to assign it to a transportable package first.
• The check variant must exist on the system. ABAP_CLOUD_READINESS is the standard name on SAP BTP ABAP / S/4HANA Cloud, but on-premise systems often ship S4HANA_READINESS_<release> (e.g. S4HANA_READINESS_2023) or SAP_CLOUD_PLATFORM_DEFAULT instead. If the named variant is absent ARC-1 rejects the call (SAP would silently run DEFAULT) — list the real names with SAPDiagnose(action="atc_variants"), or omit variant to bind the system's configured default.

1a. Run ATC on the target object

SAPDiagnose(action="atc", type="<type>", name="<object_name>", variant="<variant>")

If no variant was specified, run with the system default first (omitting variant makes ARC-1 resolve systemCheckVariant from ATC customizing and send it explicitly — SAP's own empty-checkVariant behavior would run the Code Inspector variant DEFAULT instead):

SAPDiagnose(action="atc", type="<type>", name="<object_name>")

Then suggest a readiness variant if available (e.g., S4HANA_READINESS_2023, ABAP_CLOUD_READINESS). If a run returns zero findings on code you expect to be flagged, first confirm the object is not in $TMP (see the gotcha above).

1b. For package-level checks — find all objects first

SAPRead(type="DEVC", name="<package_name>")

This returns all objects in the package. Then run ATC on each object individually. For large packages, prioritize PROG, CLAS, FUGR, FUNC types first as they typically contain the most migration-relevant findings.

Step 2: Group and Prioritize Findings

Organize findings into a structured summary. Deduplicate findings with the same checkTitle across multiple locations.

Summary Table

Present findings grouped by priority and category:

Migration Readiness Report for <object_name>
=============================================

Total findings: <N>

Categories

Group findings into these categories:

• Deprecated API: Calls to functions, classes, or methods that are deprecated or not released in S/4HANA
• Syntax Change: Obsolete ABAP statements that must be replaced
• Semantic Change: Behavior differences in S/4HANA (e.g., changed table structures, removed fields)
• Performance: Patterns that need optimization for S/4HANA
• Simplification: Items from the S/4HANA simplification list

Ask the user: "Which findings should I explain and fix? (all / specific numbers / errors only)"

Step 3: Explain Findings

For each selected finding, provide a detailed explanation.

3a. Read the affected source code

Show the code context around each finding (the line with the issue and a few lines before/after).

3b. Search documentation for migration guidance

For specific simplification items:

3c. Search SAP Notes (if SAP Notes MCP is available)

3d. Present explanation for each finding

For each finding, present:

• What: The finding description and where it occurs (file, line)
• Why: Why this is a problem for S/4HANA (compatibility, removal, behavior change)
• Replacement: The recommended modern ABAP pattern or API to use instead
• Impact: Risk level of the change (low = syntax swap, medium = logic change, high = redesign needed)

Step 4: Generate Fix Proposals

For each fixable finding, generate replacement code based on documentation and modern ABAP patterns.

4a. Check SAP quickfix first (before LLM-generated fixes)

For each finding location, first check whether SAP provides a native quickfix:

If proposals are returned:

• Present them as SAP-verified fixes (higher confidence than LLM-generated fixes)
• If the user selects one, apply it and get exact text deltas:

• apply_quickfix returns ranged text deltas — it does not persist. Apply the returned deltas to the source yourself, then write the result via SAPWrite(action="update"). When applying multiple fixes to the same object, re-resolve each finding's line after each write (earlier edits shift later line numbers), or fix top-to-bottom.

Quickfix availability is system-dependent. SAP only offers quickfix proposals where the system has the corresponding check/cloudification content installed. On a bare ABAP trial or a system without the Clean-Core remediation content, getFixProposals returns [] and ATC findings carry hasQuickfix=false — that's expected, not a bug. In that case skip straight to LLM-generated fixes (the options below). Prefer SAP quickfixes only when they actually come back.

Match the proposal to the finding — don't blindly apply proposals[0]. quickfix returns every proposal applicable at that source position, which often includes generic refactorings unrelated to the finding (verified live on S/4HANA 2023: a position returned "Rename", "Convert to attribute", "Convert to importing parameter", "Extract local variable", …). Pick the proposal whose name/description actually addresses the finding; ignore the rest.

Refactoring-style proposals can't be auto-applied here. Proposals whose uri contains /providers/refactoring/ (rename / convert-to-X / extract / introduce) are interactive refactorings that ride the separate /sap/bc/adt/refactorings multi-step flow — apply_quickfix returns HTTP 500 for them (verified live). They are not finding fixes; skip them for automated apply and fall back to an LLM-generated fix. Only proposals from non-refactoring providers apply cleanly through apply_quickfix.

Fix Options

Present 4 options per finding:

1. Apply — Auto-write the fix via ARC-1
2. Show — Display the before/after diff without applying
3. Skip — Move to the next finding
4. SAP Quick Fix — Apply SAP's quickfix proposal when available (preferred over LLM-generated fix)

Group related fixes that can be applied together (e.g., multiple deprecated statements in the same method).

Common Migration Patterns

Use these replacement patterns when generating fixes:

Step 5: Apply Selected Fixes

5a. Apply fixes

For method-level fixes in classes:

For full-source updates (programs, functions):

5b. Validate after each batch of fixes

If syntax errors are introduced: revert by writing back the original source and report the issue.

5c. Activate

Step 6: Re-validate

Run ATC again to confirm findings are resolved:

SAPDiagnose(action="atc", type="<type>", name="<object_name>", variant="<variant>")

Report results

Present a final summary:

Error Handling

Common Issues and Fixes

Notes

BTP vs On-Premise Differences

• BTP: Limited ATC variants — primarily cloud readiness checks. BTP objects already use ABAP Cloud syntax, so migration focus is different: deprecated released APIs, not classic ABAP constructs. Fewer findings expected since ABAP Cloud enforces modern patterns.
• On-Premise: Full range of S/4HANA readiness variants available (2020, 2021, 2022, 2023+). Classic ABAP objects may have many findings. FORM/PERFORM, function modules, classic reports, and DB views are common migration targets. Custom Code Migration Worklist (SCMA) may provide additional context.

Quickfix Availability

• SAP quickfixes are available for many common ATC findings (for example obsolete statements, missing declarations, straightforward syntax issues).
• Not every finding has a quickfix. Deprecated API replacements and architecture-level redesign usually still require manual/LLM-guided refactoring.

What This Skill Does NOT Do

• No transport management: User is responsible for creating and releasing transport requests
• No migration dossier: Handles one object or one package finding workflow — for reviewed, saved, or visual package-level dossiers, use sap-migration-dossier
• No custom ATC variant creation: Uses existing ATC variants on the system
• No table structure migration: Cannot modify DDIC table structures (e.g., field length changes for S/4HANA)
• No test execution: Does not run regression tests after fixes — user should validate manually or use generate-abap-unit-test skill

When to Use This Skill

• When preparing custom code for S/4HANA migration
• When checking if code meets ABAP Cloud readiness standards
• When investigating ATC findings and needing explanation + fix proposals
• When modernizing legacy ABAP code patterns (FORM, obsolete statements)
• NOT for greenfield development — use generate-rap-service for new objects