docs(lints): Provide solution for transitive pinning

Author: epage

src/cargo/lints/rules/unused_dependencies.rs

@@ -52,7 +52,8 @@ Examples:
 
 There can be false positives when depending on a transitive dependency to activate a feature.
 
-There an be false positives when pinning the version of a transitive dependency in `Cargo.toml`.
+For false positives from pinning the version of a transitive dependency in `Cargo.toml`,
+move the dependency to the `target."cfg(false)".dependencies` table.
 
 ### Example
 

src/doc/src/reference/lints.md

@@ -450,7 +450,8 @@ Examples:
 
 There can be false positives when depending on a transitive dependency to activate a feature.
 
-There an be false positives when pinning the version of a transitive dependency in `Cargo.toml`.
+For false positives from pinning the version of a transitive dependency in `Cargo.toml`,
+move the dependency to the `target."cfg(false)".dependencies` table.
 
 ### Example
 

tests/testsuite/lints/unused_dependencies.rs

@@ -1212,6 +1212,8 @@ fn pinned_transitive_dep() {
 
             [dependencies]
             intermediate = "0.1.0"
+
+            [target."cfg(false)".dependencies]
             transitive = "=0.1.1"
 
             [lints.cargo]
@@ -1237,17 +1239,6 @@ fn pinned_transitive_dep() {
 [CHECKING] transitive v0.1.1
 [CHECKING] intermediate v0.1.0
 [CHECKING] foo v0.1.0 ([ROOT]/foo)
-[WARNING] unused dependency
-  --> Cargo.toml:10:13
-   |
-10 |             transitive = "=0.1.1"
-   |             ^^^^^^^^^^^^^^^^^^^^^
-   |
-   = [NOTE] `cargo::unused_dependencies` is set to `warn` by default
-[HELP] remove the dependency
-   |
-10 -             transitive = "=0.1.1"
-   |
 [FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
 
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