detect-static-dependencies

Detect Static Dependencies

Scan a C# codebase for calls to hard-to-test static APIs and produce a ranked report showing which statics appear most frequently, which files are most affected, and which abstractions already exist in the .NET ecosystem to replace them.

When to Use

• Auditing a project's testability before adding unit tests
• Understanding the scope of static coupling in a legacy codebase
• Prioritizing which statics to wrap first (highest-frequency wins)
• Creating a migration plan for incremental testability improvements

Response Guidelines

• Scale the response to the user's request. A question about a specific category (e.g., "find time statics") should focus on that category with file locations and counts, not produce a full report across all categories.
• When the user provides a specific file or directory path, scan only that scope — do not expand to the entire solution unless asked.
• The full structured report format in Step 4 is for comprehensive audit requests. For focused questions, return only the relevant subset (e.g., category summary + affected files for the requested category).

When Not to Use

• The user wants wrappers generated (hand off to generate-testability-wrappers)
• The user wants mechanical migration done (hand off to migrate-static-to-wrapper)
• The statics are already behind interfaces or TimeProvider
• The code is not C# / .NET

Inputs

Workflow

Step 1: Determine scan scope

Resolve the target to a set of .cs files:

• If a .cs file, scan that single file.
• If a directory, scan all .cs files recursively (excluding obj/, bin/).
• If a .csproj, find its directory and scan .cs files within.
• If a .sln, parse it, find all project directories, and scan .cs files across all projects.

Always exclude obj/, bin/, and any user-specified exclusion patterns.

Step 2: Search for static dependency patterns

Scan each file for calls matching these categories:

Step 3: Aggregate and rank results

Count each call site across the entire scan scope — including the instance-member call sites covered by the rules below, not only static ones.

Counting rules — inaccurate totals are the main way this report loses to an ad-hoc scan:

• One authoritative total. Every call site you found belongs in the category summary and the grand total. Never park real findings in an "additional observations" section that the totals exclude.
• Classify by what the member touches, not by whether it is static. Instance members that reach the same untestable resource still count and belong in the matching category (new FileInfo(path).LastWriteTimeUtc → File System; httpClient.GetAsync(...) → Network). Say "hidden dependency", not "static", when the member is an instance call.
• Exclude deterministic pure helpers from the "needs wrapping" total. Path.Combine, Path.GetExtension, Path.GetFileName, and Math.*/string.* statics take no ambient input and are trivially testable. List them, if at all, in a separate "no action needed" note — never as testability blockers.
• Cover every category before reporting — time, file system, environment, network, console, process, randomness (new Random(), Guid.NewGuid()), culture (CultureInfo.CurrentCulture), and serialization/statics such as JsonSerializer. Omitting a category that is present is an under-count.
• Give file:line for every occurrence so the user can jump straight to it.
• Reconcile before publishing. The category totals, the top-patterns table, and the per-file table must sum to the same grand total.

Produce a summary with:

1. Category summary — total call sites per category (time, filesystem, env, etc.)
2. Top patterns — the 10 most frequent individual patterns ranked by count
3. Most affected files — files with the highest number of static dependencies
4. Existing abstractions available — for each category, note the recommended .NET abstraction:
   • Time → TimeProvider (built-in since .NET 8)
   • File system → System.IO.Abstractions (NuGet package)
   • HTTP → IHttpClientFactory (built-in)
   • Environment → custom IEnvironmentProvider
   • Console → custom IConsole or ILogger
   • Process → custom IProcessRunner

Step 4: Present the report

Format the output as a structured report:

## Static Dependency Report

**Scope**: <project/solution name>
**Files scanned**: <count>
**Total static call sites**: <count>

### Category Summary
| Category     | Call Sites | Recommended Abstraction |
|-------------|-----------|------------------------|
| Time         | 42        | TimeProvider (.NET 8+) |
| File System  | 31        | System.IO.Abstractions |
| Environment  | 12        | IEnvironmentProvider   |
| ...          | ...       | ...                    |

### Top 10 Patterns
| # | Pattern             | Count | Files |
|---|---------------------|-------|-------|
| 1 | DateTime.UtcNow     | 28    | 14    |
| 2 | File.ReadAllText    | 18    | 9     |
| ...                                      |

### Most Affected Files
| File                          | Static Calls | Categories          |
|-------------------------------|-------------|---------------------|
| Services/OrderProcessor.cs    | 12          | Time, FileSystem    |
| ...                                                               |

### Migration Priority
1. **Time** (42 sites) — Use `TimeProvider`, zero NuGet dependencies on .NET 8+
2. **File System** (31 sites) — Use `System.IO.Abstractions` NuGet package
3. ...

Step 5: Suggest next steps

Based on the report, recommend which category to tackle first (highest count, best built-in support). Keep this to a few lines.

Mention generate-testability-wrappers or migrate-static-to-wrapper only when the user's next action clearly needs them — a hand-off note, not a sales pitch. Never end an audit with promotional next-steps that dilute the findings.

Validation

• All .cs files in scope were scanned (check count)
• Report includes category totals, top patterns, and affected files
• Category totals, top patterns, and per-file counts reconcile to the same grand total
• Every occurrence carries a file:line location
• No findings are held outside the totals in an "additional" section
• Deterministic pure helpers (Path.Combine, Math.*) are not counted as testability blockers
• Each detected pattern has a recommended replacement listed
• obj/ and bin/ directories were excluded
• Migration priority is ordered by impact (count × ease of replacement)

Common Pitfalls