Update design for PR rust-lang#16172: Fix use_self FP on type in const generics

Author: gauravagerwala

pr-analysis-16172.md

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+# PR #16172: Workflow Design Impact Analysis
+
+## Affected Workflows
+- **Workflow 5: lint-development**: The PR modifies the `use_self` lint implementation in `clippy_lints/src/use_self.rs` to fix a false positive on types in const generics, and updates corresponding UI tests. This directly impacts lint development and integration processes, as `clippy_lints/src/` and `tests/ui/` are key relevant files for this workflow.
+- **Workflow 4: testing**: Updates to `tests/ui/use_self.rs`, `tests/ui/use_self.fixed`, and `tests/ui/use_self.stderr` affect the UI test execution, validation, and blessing mechanisms in the testing workflow.
+
+## Workflow 5 Analysis (lint-development)
+### Summary of design changes
+Specific aspects affected: The lint implementation for `use_self` (a `LateLintPass`) is updated to handle types in const generic parameters correctly, avoiding false positive suggestions of `Self` in those contexts. This refines the analysis logic during the compilation pipeline's lint execution phase.
+
+How the PR implements these changes: 
+- Adds import of `rustc_hir::Node`.
+- Introduces `ty_is_in_generic_args` function using HIR parent iteration to detect if the type is used in impl const params.
+- Adds `ty_contains_ty` for recursive type search in common container types.
+- Inserts condition `&& !ty_is_in_generic_args(cx, hir_ty)` in the type checking predicate.
+
+Potential benefits: Increases lint precision for code using const generics, reducing developer confusion from invalid suggestions. Implications: Aligns with Clippy's goal of reliable static analysis; may influence future lint designs handling generics.
+
+The \"Integration and Execution Sequence Diagram\" requires update to highlight the refined lint pass extension and execution.
+
+Updated diagram showing differences (yellow for changes, green for additions):
+
+```mermaid
+flowchart TD
+    A[Driver loads clippy_lints] --> B[Extend LintStore with lint passes]
+    B --> C[use_self LateLintPass - changed]
+    C --> D[Traverse types in impl items]
+    D --> E{Is type in const generic args? - new check}
+    E -->|No| F[Proceed with Self replacement check]
+    E -->|Yes| G[Skip suggestion - new behavior]
+    F --> H[Span lint and suggest if applicable]
+    style C fill:#ffff00
+    style E fill:#ffff00
+    style G fill:#90ee90
+    classDef change fill:#ffff00,stroke:#333,stroke-width:2px
+    classDef addition fill:#90ee90,stroke:#333,stroke-width:2px
+    class C change
+    class E change
+    class G addition
+```
+
+## Workflow 4 Analysis (testing)
+### Summary of design changes
+Specific aspects affected: UI test inputs and expected outputs for the `use_self` lint are updated to incorporate a test case for const generics false positive fix.
+
+How the PR implements these changes: 
+- `tests/ui/use_self.rs`: Adds or modifies code snippet using const generic type in impl to trigger (previously) FP.
+- `tests/ui/use_self.stderr`: Updates to reflect no lint diagnostic emitted post-fix.
+- `tests/ui/use_self.fixed`: Adjusts any expected fixed code if suggestions were involved.
+
+Potential benefits: Verifies the lint fix correctness, expands test coverage for generic features, ensures no regressions via output matching. Implications: Strengthens overall test suite robustness.
+
+The \"UI Tests Sequence Diagram\" requires update to note expanded test cases and updated validations.
+
+Updated diagram showing differences:
+
+```mermaid
+flowchart TD
+    CT[Compile-Test runs] --> CD[Invoke clippy-driver on use_self.rs test]
+    CD --> R[Run lints, including improved use_self]
+    R --> V[Validate stderr against expected]
+    subgraph PR Changes
+        testFile[(tests/ui/use_self.rs <br/> + const generic case)]:::add
+        stderr[(use_self.stderr updated <br/> no FP lint)]:::change
+        fixed[(use_self.fixed updated)]:::change
+    end
+    CT -.-> testFile
+    V -.-> stderr
+    V -.-> fixed
+    classDef add fill:#90ee90,stroke:#333,stroke-width:2px
+    classDef change fill:#ffff00,stroke:#333,stroke-width:2px
+    class testFile add
+    class stderr change
+    class fixed change
+```
+
+## Validation
+All proposed Mermaid diagrams were validated using `mmdc` (mermaid-cli) to ensure syntactic correctness and renderability to SVG.
+
+No updates to original design documents in `.exp/` are required, as the PR does not alter the high-level workflow designs, sequences, or components—only internal implementation details of a specific lint and its tests.