Implement support for base paths

Cargo.toml

@@ -33,7 +33,7 @@ cargo-platform = { path = "crates/cargo-platform", version = "0.1.5" }
 cargo-test-macro = { version = "0.3.0", path = "crates/cargo-test-macro" }
 cargo-test-support = { version = "0.4.0", path = "crates/cargo-test-support" }
 cargo-util = { version = "0.2.14", path = "crates/cargo-util" }
-cargo-util-schemas = { version = "0.5.0", path = "crates/cargo-util-schemas" }
+cargo-util-schemas = { version = "0.6.0", path = "crates/cargo-util-schemas" }
 cargo_metadata = "0.18.1"
 clap = "4.5.11"
 color-print = "0.3.6"

crates/cargo-util-schemas/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "cargo-util-schemas"
-version = "0.5.1"
+version = "0.6.0"
 rust-version = "1.80"  # MSRV:1
 edition.workspace = true
 license.workspace = true

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

@@ -767,6 +767,7 @@ pub struct TomlDetailedDependency<P: Clone = String> {
     // `path` is relative to the file it appears in. If that's a `Cargo.toml`, it'll be relative to
     // that TOML file, and if it's a `.cargo/config` file, it'll be relative to that file.
     pub path: Option<P>,
+    pub base: Option<String>,
     pub git: Option<String>,
     pub branch: Option<String>,
     pub tag: Option<String>,
@@ -806,6 +807,7 @@ impl<P: Clone> Default for TomlDetailedDependency<P> {
             registry: Default::default(),
             registry_index: Default::default(),
             path: Default::default(),
+            base: Default::default(),
             git: Default::default(),
             branch: Default::default(),
             tag: Default::default(),

src/cargo/core/features.rs

@@ -776,6 +776,7 @@ unstable_cli_options!(
     no_index_update: bool = ("Do not update the registry index even if the cache is outdated"),
     package_workspace: bool = ("Handle intra-workspace dependencies when packaging"),
     panic_abort_tests: bool = ("Enable support to run tests with -Cpanic=abort"),
+    path_bases: bool = ("Allow paths that resolve relatively to a base specified in the config"),
     profile_rustflags: bool = ("Enable the `rustflags` option in profiles in .cargo/config.toml file"),
     public_dependency: bool = ("Respect a dependency's `public` field in Cargo.toml to control public/private dependencies"),
     publish_timeout: bool = ("Enable the `publish.timeout` key in .cargo/config.toml file"),
@@ -1280,6 +1281,7 @@ impl CliUnstable {
             "package-workspace" => self.package_workspace= parse_empty(k, v)?,
             "panic-abort-tests" => self.panic_abort_tests = parse_empty(k, v)?,
             "public-dependency" => self.public_dependency = parse_empty(k, v)?,
+            "path-bases" => self.path_bases = parse_empty(k, v)?,
             "profile-rustflags" => self.profile_rustflags = parse_empty(k, v)?,
             "trim-paths" => self.trim_paths = parse_empty(k, v)?,
             "publish-timeout" => self.publish_timeout = parse_empty(k, v)?,

src/cargo/sources/path.rs

@@ -910,6 +910,11 @@ fn nested_paths(manifest: &Manifest) -> Vec<PathBuf> {
             let Some(path) = dep.path.as_ref() else {
                 continue;
             };
+            if dep.base.is_some() {
+                // Skip dependencies with base paths, if they are part of the directory tree then
+                // the outer walk will find them.
+                continue;
+            }
             nested_paths.push(PathBuf::from(path.as_str()));
         }
     }

src/cargo/util/toml/mod.rs

@@ -901,13 +901,17 @@ impl InheritableFields {
         };
         let mut dep = dep.clone();
         if let manifest::TomlDependency::Detailed(detailed) = &mut dep {
-            if let Some(rel_path) = &detailed.path {
-                detailed.path = Some(resolve_relative_path(
-                    name,
-                    self.ws_root(),
-                    package_root,
-                    rel_path,
-                )?);
+            if detailed.base.is_none() {
+                // If this is a path dependency without a base, then update the path to be relative
+                // to the workspace root instead.
+                if let Some(rel_path) = &detailed.path {
+                    detailed.path = Some(resolve_relative_path(
+                        name,
+                        self.ws_root(),
+                        package_root,
+                        rel_path,
+                    )?);
+                }
             }
         }
         Ok(dep)
@@ -2129,7 +2133,40 @@ fn to_dependency_source_id<P: ResolveToPath + Clone>(
             // always end up hashing to the same value no matter where it's
             // built from.
             if manifest_ctx.source_id.is_path() {
-                let path = manifest_ctx.root.join(path);
+                let path = if let Some(base) = orig.base.as_ref() {
+                    if !manifest_ctx.gctx.cli_unstable().path_bases {
+                        bail!("usage of path bases requires `-Z path-bases`");
+                    }
+
+                    // Look up the relevant base in the Config and use that as the root.
+                    if let Some(path_bases) = manifest_ctx
+                        .gctx
+                        .get::<Option<ConfigRelativePath>>(&format!("path-bases.{base}"))?
+                    {
+                        let path_base = path_bases.resolve_path(manifest_ctx.gctx);
+                        path_base.join(path)
+                    } else {
+                        // Otherwise, check the build-in bases.
+                        match base.as_str() {
+                            "workspace" => {
+                                if let Some(workspace_root) = find_workspace_root(manifest_ctx.root, manifest_ctx.gctx)? {
+                                    workspace_root.parent().unwrap().join(path)
+                                } else {
+                                    bail!(
+                                        "dependency ({name_in_toml}) is using the `workspace` built-in path base outside of a workspace."
+                                    )
+                                }
+                            },
+                            _ => bail!(
+                                "dependency ({name_in_toml}) uses an undefined path base `{base}`. \
+                                You must add an entry for `{base}` in the Cargo configuration [path-bases] table."
+                            )
+                        }
+                    }
+                } else {
+                    // This is a standard path with no prefix.
+                    manifest_ctx.root.join(path)
+                };
                 let path = paths::normalize_path(&path);
                 SourceId::for_path(&path)
             } else {
@@ -2855,6 +2892,7 @@ fn prepare_toml_for_publish(
                 let mut d = d.clone();
                 // Path dependencies become crates.io deps.
                 d.path.take();
+                d.base.take();
                 // Same with git dependencies.
                 d.git.take();
                 d.branch.take();