Add vim indent plugin (#8)

* Define commentstring for vim plugin
* Define comments for vim plugin
* Correct commentstring
* Update vim Makefile to handle ftplugin directory
* Rough indentation plugin implementation
* Set indent level of first line
* Improve indentation inside sections
* Indent keywords
* Tidy echoes and comments
* Handle indent plugin in Makefile
* Add 'Stage' keyword
* Tidy comments
* Add handling of apptest section

Co-authored-by: Vanessasaurus <814322+vsoch@users.noreply.github.com>
Co-authored-by: Vanessasaurus <814322+vsoch@users.noreply.github.com>

vim/Makefile

@@ -2,14 +2,18 @@ install:
 	mkdir -p ~/.vim/syntax
 	mkdir -p ~/.vim/ftdetect
 	mkdir -p ~/.vim/ftplugin
+	mkdir -p ~/.vim/indent
 	cp syntax/singularity.vim ~/.vim/syntax/
 	cp ftdetect/singularity.vim ~/.vim/ftdetect/
 	cp ftplugin/singularity.vim ~/.vim/ftplugin/
+	cp indent/singularity.vim ~/.vim/indent/
 
 uninstall:
 	rm ~/.vim/syntax/singularity.vim
 	rm ~/.vim/ftdetect/singularity.vim
 	rm ~/.vim/ftlugin/singularity.vim
+	rm ~/.vim/indent/singularity.vim
 	rmdir ~/.vim/syntax
 	rmdir ~/.vim/ftdetect
 	rmdir ~/.vim/ftplugin
+	rmdir ~/.vim/indent

vim/indent/singularity.vim

@@ -0,0 +1,70 @@
+" Singularity indent file
+
+" Only load this script if no other indent script has been loaded
+if exists("b:did_indent")
+    finish
+endif
+let b:did_indent=1
+
+" Configure other indent options
+setlocal nocindent
+setlocal nosmartindent
+setlocal autoindent
+
+" Declare function to determine indent level
+setlocal indentexpr=GetSingularityIndent(v:lnum)
+
+" Declare which keys trigger the indentation function
+setlocal indentkeys=!^F,o,O,0%,<:>
+
+" Indentation level function
+" Returns the level of indentation as an integer
+" -1 means to retain the current indentation level
+function! GetSingularityIndent(lnum)
+    let lnum = a:lnum
+
+    " The first line is at indent level 0
+    if lnum == 1
+        return 0
+    endif
+
+    let this_line = getline(lnum)
+
+    " Catch indentation triggered when typing %, for section headings set
+    " indent to level 0
+    if this_line =~ '^\s*%'
+        return 0
+    endif
+
+    " Trigger indentation when typing :, if line matches a keyword set indent
+    " to level 0
+    if this_line =~ '^\s*\(Bootstrap\|From\|Stage\|OSVersion\|MirrorURL\|Library\|Registry\|Namespace\|IncludeCmd\|Include\):'
+        return 0
+    endif
+
+
+    " Search backwards for the section lnum belongs to
+    let clnum = lnum - 1
+    while clnum > 0
+        let current_line = getline(clnum)
+
+        " If parent section is one of
+        " %setup,%files,%post,%test,%environment,%startscript,%runscript,%labels,%help
+        " increase indent one step
+        if current_line =~ '^%\(setup\|files\|post\|test\|environment\|startscript\|runscript\|labels\|help\)'
+            return indent(clnum) + &shiftwidth
+        endif
+
+        " If parent section is one of
+        " %apprun *,%applabels *,%appinstall *,%appenv *,%apphelp *,%appfiles *
+        " increase indent one step
+        if current_line =~ '^%\(apprun\|applabels\|appinstall\|appenv\|apphelp\|appfiles\|apptest\)\s*[a-zA-Z]*'
+            return indent(clnum) + &shiftwidth
+        endif
+
+        let clnum = clnum - 1
+    endwhile
+
+    " Otherwise return same indent level
+    return -1
+endfunction