Add buf linter and fixer (#4128)

* Add buf lint to linters

* Add buf format to fixers

* Fix test/linter/test_buf_lint.vader

* Fix test/fixers/test_buf_format_fixer_callback.vader

* Simplify test/test-files/proto/testfile.proto

* Add buf-lint alias and rename linter

doc/ale-proto.txt

@@ -8,13 +8,51 @@ Integration Information
 To enable `.proto` file linting, update |g:ale_linters| as appropriate:
 >
   " Enable linter for .proto files
-  let g:ale_linters = {'proto': ['protoc-gen-lint', 'protolint']}
+  let g:ale_linters = {'proto': ['buf-lint', 'protoc-gen-lint', 'protolint']}
 
 To enable `.proto` file fixing, update |g:ale_fixers| as appropriate:
 >
   " Enable linter for .proto files
-  let b:ale_fixers = {'proto': ['protolint']}
+  let b:ale_fixers = {'proto': ['buf-format', 'protolint']}
 <
+===============================================================================
+buf-format                                                *ale-proto-buf-format*
+
+  The formatter uses `buf`, a fully-featured Protobuf compiler that doesn't depend
+  on `protoc`. Make sure the `buf` binary is available in the system path, or
+  set ale_proto_buf_format_executable.
+
+g:ale_proto_buf_format_executable           *g:ale_proto_buf_format_executable*
+
+  Type: |String|
+  Default: 'buf'
+
+  This variable can be changed to modify the executable used for buf.
+
+===============================================================================
+buf-lint                                                    *ale-proto-buf-lint*
+
+  The linter uses `buf`, a fully-featured Protobuf compiler that doesn't depend
+  on `protoc`. Make sure the `buf` binary is available in the system path, or
+  set ale_proto_buf_lint_executable.
+
+g:ale_proto_buf_lint_executable               *g:ale_proto_buf_lint_executable*
+
+  Type: |String|
+  Default: 'buf'
+
+  This variable can be changed to modify the executable used for buf.
+
+g:ale_proto_buf_lint_config                       *g:ale_proto_buf_lint_config*
+
+  Type: |String|
+  Default: `''`
+
+  A path to a buf configuration file.
+
+  The path to the configuration file can be an absolute path or a relative
+  path. ALE will search for the relative path in parent directories.
+
 ===============================================================================
 protoc-gen-lint                                      *ale-proto-protoc-gen-lint*
 

doc/ale-supported-languages-and-tools.txt

@@ -430,6 +430,8 @@ Notes:
 * Prolog
   * `swipl`
 * proto
+  * `buf-format`!!
+  * `buf-lint`!!
   * `protoc-gen-lint`!!
   * `protolint`!!
 * Pug

doc/ale.txt

@@ -3060,6 +3060,8 @@ documented in additional help files.
   prolog..................................|ale-prolog-options|
     swipl.................................|ale-prolog-swipl|
   proto...................................|ale-proto-options|
+    buf-format............................|ale-proto-buf-format|
+    buf-lint..............................|ale-proto-buf-lint|
     protoc-gen-lint.......................|ale-proto-protoc-gen-lint|
     protolint.............................|ale-proto-protolint|
   pug.....................................|ale-pug-options|