Audit by Deep Research

Impacted Ordering Rules (Using Directives)

C# 10 introduces global using directives. These must be handled carefully by ordering and layout rules so the analyzers:

Ignore valid global usings,
Enforce correct ordering within global usings,
And still enforce rules for normal (non-global) usings.

This document lists the impacted rules (and one layout rule) and summarizes the behavior.

SA1200 – UsingDirectivesMustBePlacedCorrectly

Behavior with global usings

Global using directives are always top-level by language design (outside any namespace).
Historically, SA1200 reported a violation for any using outside a namespace.
This caused false positives for global usings.

Required behavior

SA1200 must not report diagnostics for global using directives.
Implementation skips global usings when collecting “outside-namespace” usings.
Documentation clarifies that global using directives are exempt from SA1200.

Tests

Files with global usings before a namespace:

global using System;
global using MyLib;

namespace Example;

No SA1200 diagnostics.

Files using top-level statements with global usings.

SA1208 – SystemUsingDirectivesMustBePlacedBeforeOtherUsingDirectives

Behavior with global usings

SA1208 requires System.* usings to appear before non-System usings.
With global usings, we effectively have two independent groups:
- Global usings.
- Non-global (normal) usings.
The rule should enforce System-first order within each group, but not across global/non-global boundaries.

Required behavior

Only compare usings that share the same global-ness:
- Global vs global.
- Non-global vs non-global.
Example:
- Violation (global group):
```
global using MyLib;
global using System;
```
- No violation (global vs local):
```
global using System;

using MyLib;
```
Even if the local using MyLib; appears before local using System;, it is still checked separately for SA1208 in the local group.

Tests

Mixed files with global and local usings:
- Check that each group enforces System.* before other namespaces.
- Confirm no cross-group comparisons.

SA1209 – UsingAliasDirectivesMustBePlacedAfterOtherUsingDirectives

Behavior with global usings

Aliased usings (using X = Y;) must appear after non-alias usings.
With global usings:
- Global alias usings must come after global non-alias usings.
- Local alias usings must come after local non-alias usings.
No comparisons should be made between global and non-global directives.

Required behavior

Only compare alias ordering within the same global/local context.

Example:

Allowed:

global using System;
global using Alias = System.Console;

using System;
using Alias2 = System.Console;

Violation examples:
- Global alias before global regular.
- Local alias before local regular.

Tests

Global-only scenarios.
Local-only scenarios.
Combined global + local scenarios.

SA1210 – UsingDirectivesMustBeOrderedAlphabeticallyByNamespace

Behavior with global usings

SA1210 enforces alphabetical ordering of usings by namespace.
With C# 10, the ordering must be evaluated:
- Separately for global usings.
- Separately for local usings.

Required behavior

Global usings form their own ordered block.
Local usings form another ordered block.
The analyzer should not compare global and local usings to each other for alphabetical order.

Tests

Files with a mix of global and local usings:
- Confirm no SA1210 diagnostics if each block is internally sorted.
- Confirm misordered entries within each block are still reported.

SA1211 – UsingAliasDirectivesMustBeOrderedAlphabeticallyByAliasName

Behavior with global usings

SA1211 orders using Alias = ... directives by alias name.
Similar to SA1210:
- Alphabetical checking applies separately to:
  - Global alias usings.
  - Local alias usings.

Required behavior

Only compare alias names within the same global/local group.
Ignore ordering relationship between a global alias and a local alias.

Tests

Separate sets of global and local alias usings, each requiring alphabetic sorting.
Ensure out-of-order alias in global block is flagged, but out-of-order relative to local block is ignored.

SA1216 – UsingStaticDirectivesMustBePlacedAtTheCorrectLocation

Behavior with global usings

SA1216 enforces this within a group:
- Normal usings.
- Then using static.
- Then alias usings.
With global usings, we essentially have two sequences:
- Global: regular → static → alias.
- Local: regular → static → alias.

Required behavior

The rule must reset its internal state when moving between global and non-global sections.
Only order within each set:
- Global static usings must appear between global regular usings and global alias usings.
- Local static usings must appear between local regular usings and local alias usings.

Tests

Violation:

global using static System.Console;
global using System;

No violation when a global static using appears before local regular usings (different group).

SA1217 – UsingStaticDirectivesMustBeOrderedAlphabetically

Behavior with global usings

SA1217 requires using static ... directives to be alphabetized by fully-qualified type name.
With global usings, global static usings and local static usings must be handled separately.

Required behavior

Alphabetical checking occurs independently for:
- Global static usings.
- Local static usings.
No cross-group comparisons.

Tests

A block of global static usings, intentionally misordered, should trigger SA1217.
Mixed global/local static usings out of order relative to each other must not cause SA1217 diagnostics.

Impacted Layout Rules

SA1516 – ElementsMustBeSeparatedByBlankLine

SA1516 controls blank lines between elements and can also enforce spacing between groups of usings (blankLinesBetweenUsingGroups in stylecop.json).

Global usings introduce a new top-level group:

The analyzer must treat transitions between:
- Global usings,
- Namespace-level usings,
- Other code,
  as potential group boundaries for blank-line rules.

Required behavior

Using directives are already grouped by type (System, regular, static, alias). This grouping now implicitly respects global vs non-global lists.
When blankLinesBetweenUsingGroups is enabled, the analyzer should:
- Consider the end of the global using block as a distinct boundary.
- Apply normal spacing rules between:
  - Global usings and file-scoped namespaces.
  - Global usings and top-level statements.
  - Global usings and namespace-level usings.

Tests

Files that contain:
- Only global usings.
- Global usings followed by file-scoped namespace or top-level statements.
- Global usings followed by namespace-level usings.
Ensure:
- Required blank lines are enforced.
- No duplicate or spurious diagnostics occur (including cases affected by earlier compiler quirks around global using lists).

Other Rule Categories

Naming, documentation, maintainability, and most readability/spacing rules are unaffected by global using directives.
Example: SA1135 (using directives must be qualified) already treats any using outside a namespace as “qualified” and thus does not require changes for global usings.

All necessary adjustments are confined to the ordering and layout rules listed above.

Sources

SA1200–SA1217 documentation and analyzers.
SA1200UsingDirectivesMustBePlacedCorrectly.cs
SA1208SystemUsingDirectivesMustBePlacedBeforeOtherUsingDirectives.cs
SA1216UsingStaticDirectivesMustBePlacedAtTheCorrectLocation.cs
SA1516CSharp11UnitTests.cs
Configuration.md and individual SA1200–SA1217 docs.

Review impact of global using directives on existing rules #3982

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