slang-module-import-without-use

Status: shipped (Phase 8.C — ADR 0021 sub-phase C, v1.5.0).

What it detects

An import Foo; statement (tree-sitter-slang import_statement node) whose tail-segment identifier Foo never appears anywhere else in the source bytes outside the import statement itself. The detection is a text-search heuristic mirroring the existing unused-cbuffer-field rule: standalone-identifier occurrences are counted using is_id_char boundaries so substrings (e.g. FooBar, xFoo) don't suppress the diagnostic.

For dotted imports (import Foo.Bar.Baz;) the rule keys on the LAST segment — that is what callers reference via Baz.api() or via Foo.Bar.Baz.api(). Empirically the tree-sitter-slang grammar parses dotted imports as an import_statement with multiple identifier children; the rule walks the children and uses the trailing one as the search key. The grammar uses import_statement (NOT import_declaration as the prompt predicted) — the latter appears in the C++ inheritance chain but is not the node-kind used for Slang's import form.

Why it matters on a GPU

Slang loads, parses, and type-checks every import-ed module regardless of whether any of its symbols are referenced in the importing translation unit. On a project with 50 shaders that all import Common; import Math; import Lighting;, an unused import in a heavily-used module bloats the per-shader compile budget by the parse-and-typecheck cost of the imported tree. For a Slang module that itself imports four other modules, the compile cost is multiplicative.

Removing dead imports is the cheapest single optimisation a Slang codebase can take to reduce shader-compile latency on hot paths (content-author iteration, shader cache misses on game launch).

Examples

Bad

slang

import Lighting;        // Imported but never referenced below.

float test(float x) { return x; }

Good

slang

import Lighting;

float test(float x) {
    return Lighting.applyAmbient(x);
}

Options

none

Fix availability

suggestion — removing the import line is mechanical, but the rule deliberately does not auto-apply. The text-search heuristic is high- precision low-recall: a real "dead import" check needs module-aware reflection (a module can re-export symbols whose names don't match the module identifier, in which case the rule misses dead imports entirely). Auto-deletion would be unsafe in those cases. The user is expected to verify before applying.

slang-module-import-without-use ​

What it detects ​

Why it matters on a GPU ​

Examples ​

Bad ​

Good ​

Options ​

Fix availability ​

See also ​