rust-analyzer for non-Cargo projects (#4118)

* rust-analyzer in non-cargo projects

rust-analyzer can also be used in non-cargo projects. This requires a
rust-project.json file in the project root [1].

Make the rust-analyzer linter search for a rust-project.json file if no
Cargo.toml file could be found.

[1]: https://rust-analyzer.github.io/manual.html#non-cargo-based-projects

* Document rust-analyzer without cargo

* Test rust-analyzer with non-cargo projects

Change the other rust tests to match the new directory structure of the
test files.

ale_linters/rust/analyzer.vim

@@ -9,9 +9,21 @@ function! ale_linters#rust#analyzer#GetCommand(buffer) abort
 endfunction
 
 function! ale_linters#rust#analyzer#GetProjectRoot(buffer) abort
+    " Try to find nearest Cargo.toml for cargo projects
     let l:cargo_file = ale#path#FindNearestFile(a:buffer, 'Cargo.toml')
 
-    return !empty(l:cargo_file) ? fnamemodify(l:cargo_file, ':h') : ''
+    if !empty(l:cargo_file)
+        return fnamemodify(l:cargo_file, ':h')
+    endif
+
+    " Try to find nearest rust-project.json for non-cargo projects
+    let l:rust_project = ale#path#FindNearestFile(a:buffer, 'rust-project.json')
+
+    if !empty(l:rust_project)
+        return fnamemodify(l:rust_project, ':h')
+    endif
+
+    return ''
 endfunction
 
 call ale#linter#Define('rust', {

doc/ale-rust.txt

@@ -26,8 +26,10 @@ Integration Information
   4. analyzer -- If you have rust-analyzer installed, you might prefer using
      this linter over cargo and rls. rust-analyzer also implements the
      Language Server Protocol for incremental compilation of Rust code, and is
-     the next iteration of rls. rust-analyzer, like rls, requires Rust files
+     the next iteration of rls. rust-analyzer either requires Rust files to be
-     to be contained in Cargo projects.
+     contained in Cargo projects or requires the project to be described in
+     the rust-project.json format:
+     https://rust-analyzer.github.io/manual.html#non-cargo-based-projects
   5. rustfmt -- If you have `rustfmt` installed, you can use it as a fixer to
      consistently reformat your Rust code.
 

test/linter/test_rust_analyzer.vader

@@ -7,12 +7,19 @@ After:
 Execute(The default executable path should be correct):
   AssertLinter 'rust-analyzer', ale#Escape('rust-analyzer')
 
-Execute(The project root should be detected correctly):
+Execute(The project root should be detected correctly in cargo projects):
   AssertLSPProject ''
 
-  call ale#test#SetFilename('../test-files/rust/test.rs')
+  call ale#test#SetFilename('../test-files/rust/cargo/testfile.rs')
 
-  AssertLSPProject ale#path#Simplify(g:dir . '/../test-files/rust')
+  AssertLSPProject ale#path#Simplify(g:dir . '/../test-files/rust/cargo')
+
+Execute(The project root should be detected correctly in non-cargo projects):
+  AssertLSPProject ''
+
+  call ale#test#SetFilename('../test-files/rust/rust-project/testfile.rs')
+
+  AssertLSPProject ale#path#Simplify(g:dir . '/../test-files/rust/rust-project')
 
 Execute(Should accept configuration settings):
   AssertLSPConfig {}

test/linter/test_rust_rls.vader

@@ -20,9 +20,9 @@ Execute(The toolchain should be ommitted if not given):
 Execute(The project root should be detected correctly):
   AssertLSPProject ''
 
-  call ale#test#SetFilename('../test-files/rust/test.rs')
+  call ale#test#SetFilename('../test-files/rust/cargo/testfile.rs')
 
-  AssertLSPProject ale#path#Simplify(g:dir . '/../test-files/rust')
+  AssertLSPProject ale#path#Simplify(g:dir . '/../test-files/rust/cargo')
 
 Execute(Should accept configuration settings):
   AssertLSPConfig {}

test/linter/test_rustc.vader

@@ -13,9 +13,9 @@ Execute(The options should be configurable):
   AssertLinter 'rustc', 'rustc --error-format=json --foo -'
 
 Execute(Some default paths should be included when the project is a Cargo project):
-  call ale#test#SetFilename('../test-files/cargo/test.rs')
+  call ale#test#SetFilename('../test-files/rust/cargo/testfile.rs')
 
   AssertLinter 'rustc', 'rustc --error-format=json --emit=mir -o /dev/null'
-  \   . ' -L ' . ale#Escape(ale#path#GetAbsPath(g:dir,  '../test-files/cargo/target/debug/deps'))
+  \   . ' -L ' . ale#Escape(ale#path#GetAbsPath(g:dir,  '../test-files/rust/cargo/target/debug/deps'))
-  \   . ' -L ' . ale#Escape(ale#path#GetAbsPath(g:dir, '../test-files/cargo/target/release/deps'))
+  \   . ' -L ' . ale#Escape(ale#path#GetAbsPath(g:dir, '../test-files/rust/cargo/target/release/deps'))
   \   . ' -'