Add config-based path shorthands

src/bin/cargo/cli.rs

@@ -45,6 +45,7 @@ Available unstable (nightly-only) flags:
     -Z terminal-width      -- Provide a terminal width to rustc for error truncation
     -Z namespaced-features -- Allow features with `dep:` prefix
     -Z weak-dep-features   -- Allow `dep_name?/feature` feature syntax
+    -Z path-bases          -- Allow paths that resolve relatively to a base specified in the config
 
 Run with 'cargo -Z [FLAG] [SUBCOMMAND]'"
         );

src/cargo/core/features.rs

@@ -446,6 +446,7 @@ pub struct CliUnstable {
     pub extra_link_arg: bool,
     pub credential_process: bool,
     pub configurable_env: bool,
+    pub path_bases: bool,
 }
 
 const STABILIZED_COMPILE_PROGRESS: &str = "The progress bar is now always \
@@ -631,6 +632,7 @@ impl CliUnstable {
             "weak-dep-features" => self.weak_dep_features = parse_empty(k, v)?,
             "extra-link-arg" => self.extra_link_arg = parse_empty(k, v)?,
             "credential-process" => self.credential_process = parse_empty(k, v)?,
+            "path-bases" => self.path_bases = parse_empty(k, v)?,
             "compile-progress" => stabilized_warn(k, "1.30", STABILIZED_COMPILE_PROGRESS),
             "offline" => stabilized_err(k, "1.36", STABILIZED_OFFLINE)?,
             "cache-messages" => stabilized_warn(k, "1.40", STABILIZED_CACHE_MESSAGES),

src/cargo/util/toml/mod.rs

@@ -23,7 +23,9 @@ use crate::core::{GitReference, PackageIdSpec, SourceId, WorkspaceConfig, Worksp
 use crate::sources::{CRATES_IO_INDEX, CRATES_IO_REGISTRY};
 use crate::util::errors::{CargoResult, CargoResultExt, ManifestError};
 use crate::util::interning::InternedString;
-use crate::util::{self, paths, validate_package_name, Config, IntoUrl};
+use crate::util::{
+    self, config::ConfigRelativePath, paths, validate_package_name, Config, IntoUrl,
+};
 
 mod targets;
 use self::targets::targets;
@@ -260,6 +262,7 @@ pub struct DetailedTomlDependency {
     /// crates published by other users.
     registry_index: Option<String>,
     path: Option<String>,
+    base: Option<String>,
     git: Option<String>,
     branch: Option<String>,
     tag: Option<String>,
@@ -1004,6 +1007,7 @@ impl TomlManifest {
                     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();
@@ -1764,7 +1768,31 @@ impl DetailedTomlDependency {
                 // always end up hashing to the same value no matter where it's
                 // built from.
                 if cx.source_id.is_path() {
-                    let path = cx.root.join(path);
+                    let path = if let Some(base) = self.base.as_ref() {
+                        if !cx.config.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(base_path) = cx
+                            .config
+                            .get::<Option<ConfigRelativePath>>(&format!("base.{}", base))?
+                        {
+                            let base_path = base_path.resolve_path(cx.config);
+                            base_path.join(path)
+                        } else {
+                            bail!(
+                                "path base `{}` is undefined for path `{}`. \
+                                 You must specify a path for `base.{}` in your cargo configuration.",
+                                base,
+                                path,
+                                base
+                            );
+                        }
+                    } else {
+                        // This is a standard path with no prefix.
+                        cx.root.join(path)
+                    };
                     let path = util::normalize_path(&path);
                     SourceId::for_path(&path)?
                 } else {

tests/testsuite/path.rs

@@ -529,6 +529,175 @@ Caused by:
         .run();
 }
 
+#[cargo_test]
+fn path_bases_not_stable() {
+    let bar = project()
+        .at("bar")
+        .file("Cargo.toml", &basic_manifest("bar", "0.5.0"))
+        .file("src/lib.rs", "")
+        .build();
+
+    fs::create_dir(&paths::root().join(".cargo")).unwrap();
+    fs::write(
+        &paths::root().join(".cargo/config"),
+        &format!(
+            "[base]\ntest = '{}'",
+            bar.root().parent().unwrap().display()
+        ),
+    )
+    .unwrap();
+
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+                [package]
+
+                name = "foo"
+                version = "0.5.0"
+                authors = ["wycats@example.com"]
+
+                [dependencies.bar]
+                path = 'bar'
+                base = 'test'
+            "#,
+        )
+        .file("src/lib.rs", "")
+        .build();
+
+    p.cargo("build")
+        .with_status(101)
+        .with_stderr(
+            "\
+error: failed to parse manifest at `[..]/foo/Cargo.toml`
+
+Caused by:
+  Usage of path bases requires `-Z path-bases`
+",
+        )
+        .run();
+}
+
+#[cargo_test]
+fn patch_with_base() {
+    let bar = project()
+        .at("bar")
+        .file("Cargo.toml", &basic_manifest("bar", "0.5.0"))
+        .file("src/lib.rs", "pub fn hello() {}")
+        .build();
+    Package::new("bar", "0.5.0").publish();
+
+    fs::create_dir(&paths::root().join(".cargo")).unwrap();
+    fs::write(
+        &paths::root().join(".cargo/config"),
+        &format!(
+            "[base]\ntest = '{}'",
+            bar.root().parent().unwrap().display()
+        ),
+    )
+    .unwrap();
+
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+                [package]
+                name = "foo"
+                version = "0.5.0"
+                authors = ["wycats@example.com"]
+                edition = "2018"
+
+                [dependencies.bar]
+                bar = "0.5.0"
+
+                [patch.crates-io.bar]
+                path = 'bar'
+                base = 'test'
+            "#,
+        )
+        .file("src/lib.rs", "use bar::hello as _;")
+        .build();
+
+    p.cargo("build -v -Zpath-bases")
+        .masquerade_as_nightly_cargo()
+        .run();
+}
+
+#[cargo_test]
+fn path_with_base() {
+    let bar = project()
+        .at("bar")
+        .file("Cargo.toml", &basic_manifest("bar", "0.5.0"))
+        .file("src/lib.rs", "")
+        .build();
+
+    fs::create_dir(&paths::root().join(".cargo")).unwrap();
+    fs::write(
+        &paths::root().join(".cargo/config"),
+        &format!(
+            "[base]\ntest = '{}'",
+            bar.root().parent().unwrap().display()
+        ),
+    )
+    .unwrap();
+
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+                [package]
+
+                name = "foo"
+                version = "0.5.0"
+                authors = ["wycats@example.com"]
+
+                [dependencies.bar]
+                path = 'bar'
+                base = 'test'
+            "#,
+        )
+        .file("src/lib.rs", "")
+        .build();
+
+    p.cargo("build -v -Zpath-bases")
+        .masquerade_as_nightly_cargo()
+        .run();
+}
+
+#[cargo_test]
+fn unknown_base() {
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+                [package]
+
+                name = "foo"
+                version = "0.5.0"
+                authors = ["wycats@example.com"]
+
+                [dependencies.bar]
+                path = 'bar'
+                base = 'test'
+            "#,
+        )
+        .file("src/lib.rs", "")
+        .build();
+
+    p.cargo("build -Zpath-bases")
+        .masquerade_as_nightly_cargo()
+        .with_status(101)
+        .with_stderr(
+            "\
+error: failed to parse manifest at `[..]/foo/Cargo.toml`
+
+Caused by:
+  path base `test` is undefined for path `bar`. You must specify a path for `base.test` in your cargo configuration.
+",
+        )
+        .run();
+}
+
 #[cargo_test]
 fn override_relative() {
     let bar = project()