microsoft/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

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

| Input | Required | Description | |-------|----------|-------------| | Target path | Yes | A file, directory, project (.csproj), or solution (.sln) to scan | | Exclusion patterns | No | Glob patterns to skip (e.g., **/obj/**, **/Migrations/**) | | Category filter | No | Limit to specific categories: time, filesystem, environment, network, console, process |

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:

| Category | Patterns to search for | Recommended replacement | |----------|----------------------|------------------------| | Time | DateTime.Now, DateTime.UtcNow, DateTime.Today, DateTimeOffset.Now, DateTimeOffset.UtcNow, Task.Delay(, new CancellationTokenSource(TimeSpan | TimeProvider (.NET 8+) | | File System | File.ReadAllText(, File.WriteAllText(, File.Exists(, File.Delete(, File.Copy(, File.Move(, Directory.Exists(, Directory.CreateDirectory(, Directory.GetFiles(, Directory.Delete(, Path.Combine(, Path.GetTempPath( | IFileSystem (System.IO.Abstractions NuGet) | | Environment | Environment.GetEnvironmentVariable(, Environment.SetEnvironmentVariable(, Environment.MachineName, Environment.UserName, Environment.CurrentDirectory, Environment.Exit( | Custom IEnvironmentProvider | | Network | new HttpClient(, HttpClient.GetAsync(, HttpClient.PostAsync(, HttpClient.SendAsync( | IHttpClientFactory (built-in) | | Console | Console.WriteLine(, Console.ReadLine(, Console.Write(, Console.ReadKey( | IConsole wrapper or ILogger | | Process | Process.Start(, Process.GetCurrentProcess(, Process.GetProcessesByName( | Custom IProcessRunner |

Step 3: Aggregate and rank results

Count each static call pattern across the entire scan scope. 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 (fewest dependencies, best built-in support)
• Whether to use generate-testability-wrappers for custom wrapper generation
• Whether to use migrate-static-to-wrapper for mechanical bulk migration

Validation

• [ ] All .cs files in scope were scanned (check count)
• [ ] Report includes category totals, top patterns, and affected files
• [ ] 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

| Pitfall | Solution | |---------|----------| | Scanning obj/ or generated code | Always exclude obj/, bin/, and *.Designer.cs | | Counting wrapped calls as statics | Check if the call is behind an interface or injected service before counting | | Missing statics inside lambdas/LINQ | Search covers all code within .cs files, including lambdas | | Recommending TimeProvider on < .NET 8 | Check TargetFramework in .csproj — if < net8.0, recommend NodaTime.IClock or custom ISystemClock | | Ignoring test projects | Only scan production code — exclude *.Tests.csproj projects from the scan |