feat: support target.triple.rustdocflags officially

`CARGO_TARGET_<TRIPLE>_RUSTDOCFLAGS` was accidentally accepted somehow,
so support both config and env officially,
given that removing env support would be a breaking change.

Author: weihanglo

src/cargo/core/compiler/build_context/target_info.rs

@@ -800,7 +800,6 @@ fn rustflags_from_target(
                         .as_ref()
                         .map(|rustflags| (key, &rustflags.val)),
                     // `target.cfg(…).rustdocflags` is currently not supported.
-                    // In fact, neither is `target.<triple>.rustdocflags`.
                     Flags::Rustdoc => None,
                 }
             })

src/cargo/util/config/target.rs

@@ -27,6 +27,8 @@ pub struct TargetConfig {
     pub runner: OptValue<PathAndArgs>,
     /// Additional rustc flags to pass.
     pub rustflags: OptValue<StringList>,
+    /// Additional rustdoc flags to pass.
+    pub rustdocflags: OptValue<StringList>,
     /// The path of the linker for this target.
     pub linker: OptValue<ConfigRelativePath>,
     /// Build script override for the given library name.
@@ -98,6 +100,7 @@ pub(super) fn load_host_triple(gctx: &GlobalContext, triple: &str) -> CargoResul
         Ok(TargetConfig {
             runner: None,
             rustflags: None,
+            rustdocflags: None,
             linker: None,
             links_overrides: BTreeMap::new(),
         })
@@ -118,6 +121,7 @@ fn load_config_table(gctx: &GlobalContext, prefix: &str) -> CargoResult<TargetCo
     // environment variables would not work.
     let runner: OptValue<PathAndArgs> = gctx.get(&format!("{}.runner", prefix))?;
     let rustflags: OptValue<StringList> = gctx.get(&format!("{}.rustflags", prefix))?;
+    let rustdocflags: OptValue<StringList> = gctx.get(&format!("{}.rustdocflags", prefix))?;
     let linker: OptValue<ConfigRelativePath> = gctx.get(&format!("{}.linker", prefix))?;
     // Links do not support environment variables.
     let target_key = ConfigKey::from_str(prefix);
@@ -128,6 +132,7 @@ fn load_config_table(gctx: &GlobalContext, prefix: &str) -> CargoResult<TargetCo
     Ok(TargetConfig {
         runner,
         rustflags,
+        rustdocflags,
         linker,
         links_overrides,
     })
@@ -144,7 +149,7 @@ fn parse_links_overrides(
         // Skip these keys, it shares the namespace with `TargetConfig`.
         match lib_name.as_str() {
             // `ar` is a historical thing.
-            "ar" | "linker" | "runner" | "rustflags" => continue,
+            "ar" | "linker" | "runner" | "rustflags" | "rustdocflags" => continue,
             _ => {}
         }
         let mut output = BuildOutput::default();

tests/testsuite/rustdocflags.rs

@@ -177,13 +177,10 @@ fn target_triple_rustdocflags_works() {
         .with_stderr_contains("[RUNNING] `rustdoc[..]--cfg[..]foo[..]`")
         .run();
 
-    // target.triple.rustdocflags in config is not supported.
+    // target.triple.rustdocflags in config works
     p.cargo("doc -v")
         .arg("--config")
         .arg(format!("target.{host}.rustdocflags=['--cfg', 'foo']"))
-        .with_status(101)
-        .with_stderr(format!(
-            "[ERROR] expected a table, but found a array for `target.{host}.rustdocflags` in --config cli option"
-        ))
+        .with_stderr_contains("[RUNNING] `rustdoc[..]--cfg[..]foo[..]`")
         .run();
 }