wip: Attempt at making cargo working on whole project as documented

(Make cargo work on whole project as documented)

According to `:help ale-integration-rust`, using cargo as a linter should
check the entire project. It appears this was the case initially, but it
broke somewhere along the way.

Setting `filename` to the output in the handler and avoid filtering the
spans on `file_name` goes a long way in restoring the intended behavior.

However test cases fail, even after attempting to update them. Please
see next commit.

4 files changed, 21 insertions, 1 deletions

diff --git a/ale_linters/rust/cargo.vim b/ale_linters/rust/cargo.vim
index 37fd10a8..e5fe888d 100644
--- a/ale_linters/rust/cargo.vim
+++ b/ale_linters/rust/cargo.vim
@@ -12,6 +12,7 @@ call ale#Set('rust_cargo_include_features', '')
 call ale#Set('rust_cargo_use_clippy', 0)
 call ale#Set('rust_cargo_clippy_options', '')
 call ale#Set('rust_cargo_target_dir', '')
+call ale#Set('rust_only_current_buffer', '0')
 
 function! ale_linters#rust#cargo#GetCargoExecutable(bufnr) abort
     if ale#path#FindNearestFile(a:bufnr, 'Cargo.toml') isnot# ''
diff --git a/ale_linters/rust/rustc.vim b/ale_linters/rust/rustc.vim
index bc6431ba..c7a06cc7 100644
--- a/ale_linters/rust/rustc.vim
+++ b/ale_linters/rust/rustc.vim
@@ -2,6 +2,10 @@
 " Description: rustc for rust files
 
 call ale#Set('rust_rustc_options', '--emit=mir -o /dev/null')
+" FIXME Both cargo and rustc uses ale#handlers#rust#HandleRustErrors which
+"       might or might not require this, depending on the fix for [#1570]
+"       (https://github.com/dense-analysis/ale/issues/1570).
+" call ale#Set('rust_only_current_buffer', '0')
 
 function! ale_linters#rust#rustc#RustcCommand(buffer) abort
     " Try to guess the library search path. If the project is managed by cargo,
diff --git a/autoload/ale/handlers/rust.vim b/autoload/ale/handlers/rust.vim
index a7fac464..895c7878 100644
--- a/autoload/ale/handlers/rust.vim
+++ b/autoload/ale/handlers/rust.vim
@@ -49,7 +49,11 @@ function! ale#handlers#rust#HandleRustErrors(buffer, lines) abort
         endif
 
         for l:root_span in l:error.spans
-            let l:span = s:FindSpan(a:buffer, l:root_span)
+            if ale#Var(a:buffer, 'rust_only_current_buffer')
+                let l:span = s:FindSpan(a:buffer, l:root_span)
+            else
+                let l:span = l:root_span
+            endif
 
             if ale#Var(a:buffer, 'rust_ignore_secondary_spans') && !get(l:span, 'is_primary', 1)
                 continue
@@ -57,6 +61,7 @@ function! ale#handlers#rust#HandleRustErrors(buffer, lines) abort
 
             if !empty(l:span)
                 let l:output_line = {
+                \   'filename': l:span.file_name,
                 \   'lnum': l:span.line_start,
                 \   'end_lnum': l:span.line_end,
                 \   'col': l:span.column_start,
diff --git a/doc/ale-rust.txt b/doc/ale-rust.txt
index 8e846844..c51273ab 100644
--- a/doc/ale-rust.txt
+++ b/doc/ale-rust.txt
@@ -40,6 +40,16 @@ Integration Information
 
   Also note that rustc 1.18. or later is needed.
 
+===============================================================================
+TODO
+
+g:ale_rust_only_current_buffer                 *g:ale_rust_only_current_buffer*
+                                               *b:ale_rust_only_current_buffer*
+  Type: |Number|
+  Default: `0`
+
+  Option to restore buggy operation. (FIXME: The existance of this option
+  might or might not be desired.)
 
 ===============================================================================
 analyzer                                                    *ale-rust-analyzer*