Close #5002 - Support getting g:ale_root as a String

autoload/ale/lsp_linter.vim

@@ -320,6 +320,11 @@ function! ale#lsp_linter#FindProjectRoot(buffer, linter) abort
         endif
     endif
 
+    " If the global setting is a string, return that right away.
+    if type(g:ale_root) is v:t_string
+        return g:ale_root
+    endif
+
     " Try to get a global setting for the root
     if has_key(g:ale_root, a:linter.name)
         let l:Root = g:ale_root[a:linter.name]

doc/ale.txt

@@ -2334,10 +2334,8 @@ g:ale_root
   This option is used to determine the project root for a linter. If the value
   is a |Dictionary|, it maps a linter to either a |String| containing the
   project root or a |Funcref| to call to look up the root. The |Funcref| is
-  provided the buffer number as its argument.
-
-  The buffer-specific variable may additionally be a string containing the
-  project root itself.
+  provided the buffer number as its argument. If the the value is a string, it
+  will be interpreted as the project root itself.
 
   If neither variable yields a result, a linter-specific function is invoked to
   detect a project root. If this, too, yields no result, and the linter is an

test/linter/test_perl_languageserver.vader

@@ -33,11 +33,12 @@ Execute(The project root should be globally configurable):
 
     AssertLSPProject ale#path#Simplify(g:dir . '/../test-files/perl')
     unlet g:ale_root.languageserver
-    " As tracked by <https://github.com/dense-analysis/ale/issues/5002>, there
-    " is a bug with g:ale_root.
-    " While attempting to configure g:ale_root using a String might be a quite
-    " limiting setup, it would be handy for debugging. However the test case is
-    " missing here. It would unfortunately just fail.
+
+    " Configuring g:ale_root using a String works.
+    let g:ale_root = ale#path#Simplify(g:dir . '/../test-files/perl')
+
+    AssertLSPProject ale#path#Simplify(g:dir . '/../test-files/perl')
+    let g:ale_root = {}
   endfor
 
 Execute(The project root should be per buffer configurable):

test/linter/test_perl_perlnavigator.vader

@@ -32,8 +32,12 @@ Execute(The project root should be globally configurable):
 
     AssertLSPProject ale#path#Simplify(g:dir . '/../test-files/perl')
     unlet g:ale_root.perlnavigator
-    " As tracked by <https://github.com/dense-analysis/ale/issues/5002>, there
-    " is a bug with g:ale_root which is thus missing here.
+
+    " Configuring g:ale_root using a String works.
+    let g:ale_root = ale#path#Simplify(g:dir . '/../test-files/perl')
+
+    AssertLSPProject ale#path#Simplify(g:dir . '/../test-files/perl')
+    let g:ale_root = {}
   endfor
 
 Execute(The project root should be per buffer configurable):

test/lsp/test_lsp_root_detection.vader

@@ -41,6 +41,12 @@ Execute(The global variable can be a dictionary):
 
   AssertLSPProject '/some/path'
 
+Execute(The global variable can be a string):
+  let g:ale_root = '/some/path'
+  call ale#test#SetFilename('other-file.c')
+
+  AssertLSPProject '/some/path'
+
 Execute(The global variable can have funcrefs):
   let g:ale_root = {'clangd': function('Hook1'), 'golangserver': '/path'}
   call ale#test#SetFilename('other-file.c')