feat(toml): Add autolib

PR #5335 added `autobins`, etc for #5330.  Nowhere in there is
discussion of `autolib`.

Cargo script disables support for additional build-targets by disabling
discovery.
Except we don't have a way to disable discovery of `autolib`, leading to #14476.
By adding `autolib`, we can continue in that direction.

This also allows us to bypass inferring of libs on published packages,
like all other build-targets which were handled in #13849.

As this seems fairly low controversy, this insta-stabilizes the field.
In prior versions of Cargo, users will get an "unused manifest key"
warning.
For packags where this is set by `cargo publish`, the warning will be suppressed and things will work as normal.
For `cargo vendor`, the same except there will be some churn in the
vendored source as this field will now be set.
For local development, it should be rare to set `autolib` so the lack of
error by discovering a file when this is set shouldn't be a problem.

Fixes #14476

crates/cargo-util-schemas/src/manifest/mod.rs

@@ -173,6 +173,7 @@ pub struct TomlPackage {
     pub publish: Option<InheritableVecStringOrBool>,
     pub workspace: Option<String>,
     pub im_a_teapot: Option<bool>,
+    pub autolib: Option<bool>,
     pub autobins: Option<bool>,
     pub autoexamples: Option<bool>,
     pub autotests: Option<bool>,
@@ -217,6 +218,7 @@ impl TomlPackage {
             publish: None,
             workspace: None,
             im_a_teapot: None,
+            autolib: None,
             autobins: None,
             autoexamples: None,
             autotests: None,

src/cargo/util/toml/embedded.rs

@@ -8,7 +8,13 @@ use crate::GlobalContext;
 
 const DEFAULT_EDITION: crate::core::features::Edition =
     crate::core::features::Edition::LATEST_STABLE;
-const AUTO_FIELDS: &[&str] = &["autobins", "autoexamples", "autotests", "autobenches"];
+const AUTO_FIELDS: &[&str] = &[
+    "autolib",
+    "autobins",
+    "autoexamples",
+    "autotests",
+    "autobenches",
+];
 
 pub(super) fn expand_manifest(
     content: &str,
@@ -289,6 +295,7 @@ path = "/home/me/test.rs"
 autobenches = false
 autobins = false
 autoexamples = false
+autolib = false
 autotests = false
 build = false
 edition = "2021"
@@ -324,6 +331,7 @@ time = "0.1.25"
 autobenches = false
 autobins = false
 autoexamples = false
+autolib = false
 autotests = false
 build = false
 edition = "2021"
@@ -359,6 +367,7 @@ time = "0.1.25"
 autobenches = false
 autobins = false
 autoexamples = false
+autolib = false
 autotests = false
 build = false
 edition = "2021"

src/cargo/util/toml/mod.rs

@@ -334,6 +334,7 @@ fn normalize_toml(
             package_root,
             &original_package.name,
             edition,
+            original_package.autolib,
             warnings,
         )?;
         normalized_toml.bin = Some(targets::normalize_bins(
@@ -624,6 +625,7 @@ fn normalize_package_toml<'a>(
             .map(manifest::InheritableField::Value),
         workspace: original_package.workspace.clone(),
         im_a_teapot: original_package.im_a_teapot.clone(),
+        autolib: Some(false),
         autobins: Some(false),
         autoexamples: Some(false),
         autotests: Some(false),

src/cargo/util/toml/targets.rs

@@ -129,9 +129,22 @@ pub fn normalize_lib(
     package_root: &Path,
     package_name: &str,
     edition: Edition,
+    autodiscover: Option<bool>,
     warnings: &mut Vec<String>,
 ) -> CargoResult<Option<TomlLibTarget>> {
-    {
+    if is_normalized(original_lib, autodiscover) {
+        let Some(lib) = original_lib.cloned() else {
+            return Ok(None);
+        };
+
+        // Check early to improve error messages
+        validate_lib_name(&lib, warnings)?;
+
+        validate_proc_macro(&lib, "library", edition, warnings)?;
+        validate_crate_types(&lib, "library", edition, warnings)?;
+
+        Ok(Some(lib))
+    } else {
         let inferred = inferred_lib(package_root);
         let lib = original_lib.cloned().or_else(|| {
             inferred.as_ref().map(|lib| TomlTarget {
@@ -528,6 +541,17 @@ fn to_bench_targets(
     Ok(result)
 }
 
+fn is_normalized(toml_target: Option<&TomlTarget>, autodiscover: Option<bool>) -> bool {
+    if autodiscover != Some(false) {
+        return false;
+    }
+
+    let Some(toml_target) = toml_target else {
+        return true;
+    };
+    toml_target.name.is_some() && toml_target.path.is_some()
+}
+
 fn are_normalized(toml_targets: Option<&Vec<TomlTarget>>, autodiscover: Option<bool>) -> bool {
     if autodiscover != Some(false) {
         return false;

src/doc/src/reference/cargo-targets.md

@@ -323,13 +323,14 @@ configuration tables, such as `[lib]`, `[[bin]]`, `[[test]]`, `[[bench]]`, or
 standard directory layout.
 
 The automatic target discovery can be disabled so that only manually
-configured targets will be built. Setting the keys `autobins`, `autoexamples`,
+configured targets will be built. Setting the keys `autolib`, `autobins`, `autoexamples`,
 `autotests`, or `autobenches` to `false` in the `[package]` section will
 disable auto-discovery of the corresponding target type.
 
 ```toml
 [package]
 # ...
+autolib = false
 autobins = false
 autoexamples = false
 autotests = false
@@ -363,6 +364,9 @@ autobins = false
 > is `false` if at least one target is manually defined in `Cargo.toml`.
 > Beginning with the 2018 edition, the default is always `true`.
 
+> **MSRV:** Respected as of 1.27 for `autobins`, `autoexamples`, `autotests`, and `autobenches`
+
+> **MSRV:** Respected as of 1.83 for `autolib`
 
 [Build cache]: ../guide/build-cache.md
 [Rust Edition]: ../../edition-guide/index.html

src/doc/src/reference/manifest.md

@@ -30,6 +30,7 @@ Every manifest file consists of the following sections:
   * [`publish`](#the-publish-field) --- Can be used to prevent publishing the package.
   * [`metadata`](#the-metadata-table) --- Extra settings for external tools.
   * [`default-run`](#the-default-run-field) --- The default binary to run by [`cargo run`].
+  * [`autolib`](cargo-targets.md#target-auto-discovery) --- Disables library auto discovery.
   * [`autobins`](cargo-targets.md#target-auto-discovery) --- Disables binary auto discovery.
   * [`autoexamples`](cargo-targets.md#target-auto-discovery) --- Disables example auto discovery.
   * [`autotests`](cargo-targets.md#target-auto-discovery) --- Disables test auto discovery.

src/doc/src/reference/unstable.md

@@ -1314,7 +1314,7 @@ Inferred / defaulted manifest fields:
 
 Disallowed manifest fields:
 - `[workspace]`, `[lib]`, `[[bin]]`, `[[example]]`, `[[test]]`, `[[bench]]`
-- `package.workspace`, `package.build`, `package.links`, `package.autobins`, `package.autoexamples`, `package.autotests`, `package.autobenches`
+- `package.workspace`, `package.build`, `package.links`, `package.autolib`, `package.autobins`, `package.autoexamples`, `package.autotests`, `package.autobenches`
 
 The default `CARGO_TARGET_DIR` for single-file packages is at `$CARGO_HOME/target/<hash>`:
 - Avoid conflicts from multiple single-file packages being in the same directory

tests/testsuite/artifact_dep.rs

@@ -2272,6 +2272,7 @@ name = "foo"
 version = "0.1.0"
 authors = []
 build = false
+autolib = false
 autobins = false
 autoexamples = false
 autotests = false

tests/testsuite/features2.rs

@@ -1800,6 +1800,7 @@ name = "a"
 version = "0.1.0"
 authors = ["Zzz"]
 build = false
+autolib = false
 autobins = false
 autoexamples = false
 autotests = false

tests/testsuite/features_namespaced.rs

@@ -985,6 +985,7 @@ edition = "2015"
 name = "foo"
 version = "0.1.0"
 build = false
+autolib = false
 autobins = false
 autoexamples = false
 autotests = false
@@ -1112,6 +1113,7 @@ edition = "2015"
 name = "foo"
 version = "0.1.0"
 build = false
+autolib = false
 autobins = false
 autoexamples = false
 autotests = false

tests/testsuite/inheritable_workspace_fields.rs

@@ -224,6 +224,7 @@ include = [
     "Cargo.toml",
 ]
 publish = true
+autolib = false
 autobins = false
 autoexamples = false
 autotests = false
@@ -394,6 +395,7 @@ name = "bar"
 version = "0.2.0"
 authors = []
 build = false
+autolib = false
 autobins = false
 autoexamples = false
 autotests = false
@@ -533,6 +535,7 @@ name = "bar"
 version = "0.2.0"
 authors = []
 build = false
+autolib = false
 autobins = false
 autoexamples = false
 autotests = false
@@ -793,6 +796,7 @@ include = [
     "README.md",
 ]
 publish = true
+autolib = false
 autobins = false
 autoexamples = false
 autotests = false
@@ -966,6 +970,7 @@ name = "bar"
 version = "0.2.0"
 authors = []
 build = false
+autolib = false
 autobins = false
 autoexamples = false
 autotests = false