Support --filter-platform=host for cargo metadata #9423 (#16312)

This PR fixes this issue-:  #9423

src/doc/man/cargo-metadata.md

@@ -362,6 +362,7 @@ possible value.
 {{#option "`--filter-platform` _triple_" }}
 This filters the `resolve` output to only include dependencies for the
 given [target triple](../appendix/glossary.html#target).
+A literal `"host-tuple"` can be used, which will internally be substituted by the host's target.
 Without this flag, the resolve includes all targets.
 
 Note that the dependencies listed in the "packages" array still includes all

src/doc/man/generated_txt/cargo-metadata.txt

@@ -354,8 +354,10 @@ OPTIONS
        --filter-platform triple
            This filters the resolve output to only include dependencies for the
            given target triple
-           <https://doc.rust-lang.org/cargo/appendix/glossary.html#target>.
-           Without this flag, the resolve includes all targets.
+           <https://doc.rust-lang.org/cargo/appendix/glossary.html#target>. A
+           literal "host-tuple" can be used, which will internally be
+           substituted by the host’s target. Without this flag, the resolve
+           includes all targets.
 
            Note that the dependencies listed in the “packages” array still
            includes all dependencies. Each package definition is intended to be

src/doc/src/commands/cargo-metadata.md

@@ -364,6 +364,7 @@ possible value.</p>
 <dt class="option-term" id="option-cargo-metadata---filter-platform"><a class="option-anchor" href="#option-cargo-metadata---filter-platform"><code>--filter-platform</code> <em>triple</em></a></dt>
 <dd class="option-desc"><p>This filters the <code>resolve</code> output to only include dependencies for the
 given <a href="../appendix/glossary.html#target">target triple</a>.
+A literal <code>"host-tuple"</code> can be used, which will internally be substituted by the host’s target.
 Without this flag, the resolve includes all targets.</p>
 <p>Note that the dependencies listed in the “packages” array still includes all
 dependencies. Each package definition is intended to be an unaltered

src/etc/man/cargo-metadata.1

@@ -367,6 +367,7 @@ possible value.
 .RS 4
 This filters the \fBresolve\fR output to only include dependencies for the
 given \fItarget triple\fR <https://doc.rust\-lang.org/cargo/appendix/glossary.html#target>\&.
+A literal \fB"host\-tuple"\fR can be used, which will internally be substituted by the host\[cq]s target.
 Without this flag, the resolve includes all targets.
 .sp
 Note that the dependencies listed in the \[lq]packages\[rq] array still includes all

tests/testsuite/metadata.rs

@@ -3842,21 +3842,15 @@ fn filter_platform() {
         .run();
     clear();
 
-    // Filter on host, removes alt and cfg.
-    p.cargo("metadata --filter-platform")
-        .arg(&host_target)
-        .with_stderr_data(
-            str![[r#"
+    let host_filtered_stderr = str![[r#"
 [WARNING] please specify `--format-version` flag explicitly to avoid compatibility problems
 [DOWNLOADING] crates ...
 [DOWNLOADED] normal-dep v0.0.1 (registry `dummy-registry`)
 [DOWNLOADED] host-dep v0.0.1 (registry `dummy-registry`)
 
-"#]]
-            .unordered(),
-        )
-        .with_stdout_data(
-            str![[r#"
+"#]];
+
+    let host_filtered_stdout = str![[r#"
 {
   "packages": [
     {
@@ -3945,10 +3939,21 @@ fn filter_platform() {
   },
   "...": "{...}"
 }
-"#]]
-            .is_json()
-            .unordered(),
-        )
+"#]];
+
+    // Filter on host, removes alt and cfg.
+    p.cargo("metadata --filter-platform")
+        .arg(&host_target)
+        .with_stderr_data(host_filtered_stderr.clone().unordered())
+        .with_stdout_data(host_filtered_stdout.clone().is_json().unordered())
+        .run();
+    clear();
+
+    // Filter on host-tuple, should produce same result as explicit host target.
+    p.cargo("metadata --filter-platform")
+        .arg("host-tuple")
+        .with_stderr_data(host_filtered_stderr.unordered())
+        .with_stdout_data(host_filtered_stdout.is_json().unordered())
         .run();
     clear();