cargo/manifest: remember whether target names were inferred

Add a boolean state to `Target` that tells us whether the name of the
target was inferred by Cargo, or whether it was directly specified in
the Manifest.

This value will be required in the future, to allow changing the
inferred names of targets, but retaining enough information to keep
backwards compatibility.

Author: dvdhrm

src/cargo/core/manifest.rs

@@ -207,6 +207,8 @@ pub struct Target {
 struct TargetInner {
     kind: TargetKind,
     name: String,
+    // Whether the name was inferred by Cargo, or explicitly given.
+    name_inferred: bool,
     // Note that `bin_name` is used for the cargo-feature `different_binary_name`
     bin_name: Option<String>,
     // Note that the `src_path` here is excluded from the `Hash` implementation
@@ -366,6 +368,7 @@ compact_debug! {
             [debug_the_fields(
                 kind
                 name
+                name_inferred
                 bin_name
                 src_path
                 required_features
@@ -657,6 +660,7 @@ impl Target {
             inner: Arc::new(TargetInner {
                 kind: TargetKind::Bin,
                 name: String::new(),
+                name_inferred: false,
                 bin_name: None,
                 src_path,
                 required_features: None,
@@ -790,6 +794,9 @@ impl Target {
     pub fn name(&self) -> &str {
         &self.inner.name
     }
+    pub fn name_inferred(&self) -> bool {
+        self.inner.name_inferred
+    }
     pub fn crate_name(&self) -> String {
         self.name().replace("-", "_")
     }
@@ -964,6 +971,10 @@ impl Target {
         Arc::make_mut(&mut self.inner).name = name.to_string();
         self
     }
+    pub fn set_name_inferred(&mut self, inferred: bool) -> &mut Target {
+        Arc::make_mut(&mut self.inner).name_inferred = inferred;
+        self
+    }
     pub fn set_binary_name(&mut self, bin_name: Option<String>) -> &mut Target {
         Arc::make_mut(&mut self.inner).bin_name = bin_name;
         self

src/cargo/util/toml/targets.rs

@@ -247,6 +247,7 @@ fn clean_lib(
 
     let mut target = Target::lib_target(&lib.name(), crate_types, path, edition);
     configure(lib, &mut target)?;
+    target.set_name_inferred(toml_lib.map_or(true, |v| v.name.is_none()));
     Ok(Some(target))
 }