add custom build support (#62)

Support build scripts

When we're editing 'build.rs', its target kind in `cargo metadata` is 'custom-build', which we can not use as build arguments.  However, that build script will be checked by `cargo check` if we build any target in the same package.

So, if the selected target is a 'custom-build' one, we just pick another target from the same package, if any.

This commit adds tests for the build script situation.

Author: kngwyu

flycheck-rust.el

@@ -108,7 +108,7 @@ more information on setting your PATH with Emacs."))
                                (let ((json-array-type 'list))
                                  (json-read)))
                            .packages))
-      (seq-mapcat (lambda (pkg)
+      (seq-map (lambda (pkg)
                     (let-alist pkg .targets))
                   packages))))
 
@@ -128,7 +128,8 @@ the closest matching target, or nil if no targets could be found.
 See http://doc.crates.io/manifest.html#the-project-layout for a
 description of the conventional Cargo project layout."
   (-when-let* ((manifest (flycheck-rust-find-manifest file-name))
-               (targets (flycheck-rust-get-cargo-targets manifest)))
+               (packages (flycheck-rust-get-cargo-targets manifest))
+               (targets (-flatten-n 1 packages)))
     (let ((target
            (or
             ;; If there is a target that matches the file-name exactly, pick
@@ -151,7 +152,16 @@ description of the conventional Cargo project layout."
                                             (file-name-directory manifest)))))
             ;; If all else fails, just pick the first target
             (car targets))))
-      (let-alist target (cons (flycheck-rust-normalize-target-kind .kind) .name)))))
+      ;; If target is 'custom-build', we pick another target from the same package (see GH-62)
+      (when (string= "custom-build" (let-alist target (car .kind)))
+        (setq target (->> packages
+                          ;; find the same package as current build-script buffer
+                          (--find (--any? (equal target it) it))
+                          (--find (not (equal target it))))))
+      (when target
+        (let-alist target
+          (cons (flycheck-rust-normalize-target-kind .kind) .name))))))
+
 
 (defun flycheck-rust-normalize-target-kind (kinds)
   "Return the normalized target name from KIND.

tests/build-script-test/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "build-script-test"
+version = "0.1.0"
+
+[dependencies]
+
+[workspace]
+members = ["lib-test"]

tests/build-script-test/build.rs

@@ -0,0 +1,4 @@
+fn main() {
+    let a = ;
+    println!("cargo:rustc-link-lib=bz2");
+}

tests/build-script-test/lib-test/Cargo.toml

@@ -0,0 +1,5 @@
+[package]
+name = "lib-test"
+version = "0.1.0"
+
+[dependencies]

tests/build-script-test/lib-test/build.rs

@@ -0,0 +1,6 @@
+fn main() {
+    let a = 0;
+    println!("cargo:rustc-link-lib=zzip");
+}
+
+

tests/build-script-test/lib-test/src/lib.rs

@@ -0,0 +1,7 @@
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn it_works() {
+        assert_eq!(2 + 2, 4);
+    }
+}

tests/build-script-test/src/main.rs

@@ -0,0 +1,3 @@
+fn main() {
+    println!("Hello, world!");
+}

tests/test-rust-setup.el

@@ -41,6 +41,9 @@
 (defun lib-crate-file (file-name)
   (expand-file-name file-name "tests/custom-lib-target"))
 
+(defun build-script-crate-file (file-name)
+  (expand-file-name file-name "tests/build-script-test"))
+
 (describe
  "`flycheck-rust-find-cargo-target' associates"
 
@@ -118,4 +121,14 @@
      (expect
       (car (flycheck-rust-find-cargo-target (lib-crate-file "src/lib.rs")))
       :to-equal "lib"))
+
+ (it "'build.rs' to any target in the same workspace member (parent)"
+     (expect
+      (flycheck-rust-find-cargo-target (build-script-crate-file "build.rs"))
+      :to-equal (cons "bin" "build-script-test")))
+
+ (it "'build.rs' to any target in the same workspace member (child)"
+     (expect
+      (flycheck-rust-find-cargo-target (build-script-crate-file "lib-test/build.rs"))
+      :to-equal (cons "lib" "lib-test")))
  )