Allow syntax inclusion, by going match → regiontopic/allow-embed_squashed4mr

Restructure syntax highlighting, using context aware `syntax region`
rather `syntax match` statements requiring to match on line start
anchors. This should be functionally identical when editing ordinary
todo.txt files. The advantage is that this also allows reusing this
syntax file within other file formats.

Without this commit, attempting to embed todo.txt snippets in other file
formats might result in only partial syntax highlighting. With TodoStart
marking the start of each line, the grammar allows full syntax
highlighting in case the snippet starts or ends on a non-line
boundaries.

Consider for example these four lines of prio/syntax.vim, for my purely
personal `prio` file format:

    syntax include @Todo syntax/todo.vim
    hi! def link prioLabel Label
    sy region prioLabel start="^\s*TODO:" end="\s*" nextgroup=prioTodo
    sy region prioTodo contained start=/./ end=/$/ contains=@TodoStart

This commit and the above configuration allows syntax highlighting of
any todo.txt row prefixed by `TODO:` in those files.  Making actionable
items standing out from otherwise free-form natural language.

Given the ease of configuration, one can imagine similarly embedding
todo.txt directly in any text based file format.  Thus improving many
use cases where todo.txt files might be generated from other canonical
sources.

2 files changed, 59 insertions, 50 deletions

diff --git a/syntax/todo.vim b/syntax/todo.vim
index b4c120c..44dc87f 100644
--- a/syntax/todo.vim
+++ b/syntax/todo.vim
@@ -8,37 +8,46 @@ if exists("b:current_syntax")
     finish
 endif
 
-syntax  match  TodoDone       '^[x]\s.\+$'               contains=TodoKey,TodoDate,TodoProject,TodoContext
-syntax  match  TodoPriorityA  '^(A) .\+$'             contains=TodoKey,TodoDate,TodoProject,TodoContext,TodoDueToday,TodoOverDueDate,TodoThresholdDate
-syntax  match  TodoPriorityB  '^(B) .\+$'             contains=TodoKey,TodoDate,TodoProject,TodoContext,TodoDueToday,TodoOverDueDate,TodoThresholdDate
-syntax  match  TodoPriorityC  '^(C) .\+$'             contains=TodoKey,TodoDate,TodoProject,TodoContext,TodoDueToday,TodoOverDueDate,TodoThresholdDate
-syntax  match  TodoPriorityD  '^(D) .\+$'             contains=TodoKey,TodoDate,TodoProject,TodoContext,TodoDueToday,TodoOverDueDate,TodoThresholdDate
-syntax  match  TodoPriorityE  '^(E) .\+$'             contains=TodoKey,TodoDate,TodoProject,TodoContext,TodoDueToday,TodoOverDueDate,TodoThresholdDate
-syntax  match  TodoPriorityF  '^(F) .\+$'             contains=TodoKey,TodoDate,TodoProject,TodoContext,TodoDueToday,TodoOverDueDate,TodoThresholdDate
-syntax  match  TodoPriorityG  '^(G) .\+$'             contains=TodoKey,TodoDate,TodoProject,TodoContext,TodoDueToday,TodoOverDueDate,TodoThresholdDate
-syntax  match  TodoPriorityH  '^(H) .\+$'             contains=TodoKey,TodoDate,TodoProject,TodoContext,TodoDueToday,TodoOverDueDate,TodoThresholdDate
-syntax  match  TodoPriorityI  '^(I) .\+$'             contains=TodoKey,TodoDate,TodoProject,TodoContext,TodoDueToday,TodoOverDueDate,TodoThresholdDate
-syntax  match  TodoPriorityJ  '^(J) .\+$'             contains=TodoKey,TodoDate,TodoProject,TodoContext,TodoDueToday,TodoOverDueDate,TodoThresholdDate
-syntax  match  TodoPriorityK  '^(K) .\+$'             contains=TodoKey,TodoDate,TodoProject,TodoContext,TodoDueToday,TodoOverDueDate,TodoThresholdDate
-syntax  match  TodoPriorityL  '^(L) .\+$'             contains=TodoKey,TodoDate,TodoProject,TodoContext,TodoDueToday,TodoOverDueDate,TodoThresholdDate
-syntax  match  TodoPriorityM  '^(M) .\+$'             contains=TodoKey,TodoDate,TodoProject,TodoContext,TodoDueToday,TodoOverDueDate,TodoThresholdDate
-syntax  match  TodoPriorityN  '^(N) .\+$'             contains=TodoKey,TodoDate,TodoProject,TodoContext,TodoDueToday,TodoOverDueDate,TodoThresholdDate
-syntax  match  TodoPriorityO  '^(O) .\+$'             contains=TodoKey,TodoDate,TodoProject,TodoContext,TodoDueToday,TodoOverDueDate,TodoThresholdDate
-syntax  match  TodoPriorityP  '^(P) .\+$'             contains=TodoKey,TodoDate,TodoProject,TodoContext,TodoDueToday,TodoOverDueDate,TodoThresholdDate
-syntax  match  TodoPriorityQ  '^(Q) .\+$'             contains=TodoKey,TodoDate,TodoProject,TodoContext,TodoDueToday,TodoOverDueDate,TodoThresholdDate
-syntax  match  TodoPriorityR  '^(R) .\+$'             contains=TodoKey,TodoDate,TodoProject,TodoContext,TodoDueToday,TodoOverDueDate,TodoThresholdDate
-syntax  match  TodoPriorityS  '^(S) .\+$'             contains=TodoKey,TodoDate,TodoProject,TodoContext,TodoDueToday,TodoOverDueDate,TodoThresholdDate
-syntax  match  TodoPriorityT  '^(T) .\+$'             contains=TodoKey,TodoDate,TodoProject,TodoContext,TodoDueToday,TodoOverDueDate,TodoThresholdDate
-syntax  match  TodoPriorityU  '^(U) .\+$'             contains=TodoKey,TodoDate,TodoProject,TodoContext,TodoDueToday,TodoOverDueDate,TodoThresholdDate
-syntax  match  TodoPriorityV  '^(V) .\+$'             contains=TodoKey,TodoDate,TodoProject,TodoContext,TodoDueToday,TodoOverDueDate,TodoThresholdDate
-syntax  match  TodoPriorityW  '^(W) .\+$'             contains=TodoKey,TodoDate,TodoProject,TodoContext,TodoDueToday,TodoOverDueDate,TodoThresholdDate
-syntax  match  TodoPriorityX  '^(X) .\+$'             contains=TodoKey,TodoDate,TodoProject,TodoContext,TodoDueToday,TodoOverDueDate,TodoThresholdDate
-syntax  match  TodoPriorityY  '^(Y) .\+$'             contains=TodoKey,TodoDate,TodoProject,TodoContext,TodoDueToday,TodoOverDueDate,TodoThresholdDate
-syntax  match  TodoPriorityZ  '^(Z) .\+$'             contains=TodoKey,TodoDate,TodoProject,TodoContext,TodoDueToday,TodoOverDueDate,TodoThresholdDate
-syntax  match  TodoDate       '\d\{2,4\}-\d\{2\}-\d\{2\}' contains=NONE
-syntax  match  TodoKey        '\S*\S:\S\S*'               contains=TodoDate
-syntax  match  TodoProject    '\(^\|\W\)+[^[:blank:]]\+'  contains=NONE
-syntax  match  TodoContext    '\(^\|\W\)@[^[:blank:]]\+'  contains=NONE
+syntax  cluster  TodoStart      contains=TodoTodo,TodoDone,TodoPriorityA,TodoPriorityB,TodoPriorityC,TodoPriorityD,TodoPriorityE,TodoPriorityF,TodoPriorityG,TodoPriorityH,TodoPriorityI,TodoPriorityJ,TodoPriorityK,TodoPriorityL,TodoPriorityM,TodoPriorityN,TodoPriorityO,TodoPriorityP,TodoPriorityQ,TodoPriorityR,TodoPriorityS,TodoPriorityT,TodoPriorityU,TodoPriorityV,TodoPriorityW,TodoPriorityX,TodoPriorityY,TodoPriorityZ,TodoProject,TodoContext
+syntax  cluster  TodoDoneArgs   contains=TodoKey,TodoDate,TodoProject,TodoContext
+syntax  cluster  TodoFullArgs   contains=@TodoDoneArgs,TodoDueToday,TodoOverDueDate,TodoThresholdDate
+
+hi def TodoCol0 guibg=black
+syntax  region TodoCol0  start=/^/ end=/$/ nextgroup=@TodoStart
+
+syntax  region  TodoTodo       contained start=//   end=/$/  contains=@TodoFullArgs
+syntax  region  TodoDone       contained start=/x /   end=/$/  contains=@TodoDoneArgs
+syntax  region  TodoPriorityA  contained start=/(A) / end=/$/  contains=@TodoFullArgs
+syntax  region  TodoPriorityB  contained start=/(B) / end=/$/  contains=@TodoFullArgs
+syntax  region  TodoPriorityC  contained start=/(C) / end=/$/  contains=@TodoFullArgs
+syntax  region  TodoPriorityD  contained start=/(D) / end=/$/  contains=@TodoFullArgs
+syntax  region  TodoPriorityE  contained start=/(E) / end=/$/  contains=@TodoFullArgs
+syntax  region  TodoPriorityF  contained start=/(F) / end=/$/  contains=@TodoFullArgs
+syntax  region  TodoPriorityG  contained start=/(G) / end=/$/  contains=@TodoFullArgs
+syntax  region  TodoPriorityH  contained start=/(H) / end=/$/  contains=@TodoFullArgs
+syntax  region  TodoPriorityI  contained start=/(I) / end=/$/  contains=@TodoFullArgs
+syntax  region  TodoPriorityJ  contained start=/(J) / end=/$/  contains=@TodoFullArgs
+syntax  region  TodoPriorityK  contained start=/(K) / end=/$/  contains=@TodoFullArgs
+syntax  region  TodoPriorityL  contained start=/(L) / end=/$/  contains=@TodoFullArgs
+syntax  region  TodoPriorityM  contained start=/(M) / end=/$/  contains=@TodoFullArgs
+syntax  region  TodoPriorityN  contained start=/(N) / end=/$/  contains=@TodoFullArgs
+syntax  region  TodoPriorityO  contained start=/(O) / end=/$/  contains=@TodoFullArgs
+syntax  region  TodoPriorityP  contained start=/(P) / end=/$/  contains=@TodoFullArgs
+syntax  region  TodoPriorityQ  contained start=/(Q) / end=/$/  contains=@TodoFullArgs
+syntax  region  TodoPriorityR  contained start=/(R) / end=/$/  contains=@TodoFullArgs
+syntax  region  TodoPriorityS  contained start=/(S) / end=/$/  contains=@TodoFullArgs
+syntax  region  TodoPriorityT  contained start=/(T) / end=/$/  contains=@TodoFullArgs
+syntax  region  TodoPriorityU  contained start=/(U) / end=/$/  contains=@TodoFullArgs
+syntax  region  TodoPriorityV  contained start=/(V) / end=/$/  contains=@TodoFullArgs
+syntax  region  TodoPriorityW  contained start=/(W) / end=/$/  contains=@TodoFullArgs
+syntax  region  TodoPriorityX  contained start=/(X) / end=/$/  contains=@TodoFullArgs
+syntax  region  TodoPriorityY  contained start=/(Y) / end=/$/  contains=@TodoFullArgs
+syntax  region  TodoPriorityZ  contained start=/(Z) / end=/$/  contains=@TodoFullArgs
+
+syntax  match  TodoDate       '\d\{2,4\}-\d\{2\}-\d\{2\}'      contains=NONE
+syntax  match  TodoKey        '\S*\S:\S\S*'                    contains=TodoDate
+syntax  match  TodoProject    '\(^\|\s\)+[^[:blank:]]\+'       contains=NONE
+syntax  match  TodoContext    '\(^\|\s\)@[^[:blank:]]\+'       contains=NONE
 
 let s:todayDate=strftime('%Y\-%m\-%d')
 execute 'syntax match TodoDueToday    /\v\c<due:' . s:todayDate . '>/ contains=NONE'
diff --git a/tests/todo.vader b/tests/todo.vader
index 9da6918..12f7f77 100644
--- a/tests/todo.vader
+++ b/tests/todo.vader
@@ -33,7 +33,7 @@ Execute (Syntax for done task):
   AssertEqual 'TodoProject',      SyntaxAt( 3, 54)
   AssertEqual 'TodoContext',      SyntaxAt( 3, 63)
 Execute (Syntax for active task):
-  AssertEqual '',                 SyntaxAt( 4,  1)
+  AssertEqual 'TodoTodo',         SyntaxAt( 4,  1)
   AssertEqual 'TodoOverDueDate',  SyntaxAt( 4, 13)
   AssertEqual 'TodoKey',          SyntaxAt( 4, 28)
   AssertEqual 'TodoKey',          SyntaxAt( 4, 72)
@@ -149,14 +149,14 @@ x 345678901234567890123456789012345678901234567890123456789012345678901234567890
 x   .    1    .    2    .    3    .    4    .    5    .    6    .    7    .    8  L22
 Execute (Syntax for invalid or misleading tasks):
   " Invalid done or priority
-  AssertEqual '',                 SyntaxAt( 3,  1)
-  AssertEqual '',                 SyntaxAt( 4,  1)
-  AssertEqual '',                 SyntaxAt( 5,  1)
-  AssertEqual '',                 SyntaxAt( 6,  1)
-  AssertEqual '',                 SyntaxAt( 7,  1)
-  AssertEqual '',                 SyntaxAt( 8,  1)
-  AssertEqual '',                 SyntaxAt( 9,  1)
-  AssertEqual '',                 SyntaxAt(10,  1)
+  AssertEqual 'TodoTodo',         SyntaxAt( 3,  1)
+  AssertEqual 'TodoTodo',         SyntaxAt( 4,  1)
+  AssertEqual 'TodoTodo',         SyntaxAt( 5,  1)
+  AssertEqual 'TodoTodo',         SyntaxAt( 6,  1)
+  AssertEqual 'TodoTodo',         SyntaxAt( 7,  1)
+  AssertEqual 'TodoTodo',         SyntaxAt( 8,  1)
+  AssertEqual 'TodoTodo',         SyntaxAt( 9,  1)
+  AssertEqual 'TodoTodo',         SyntaxAt(10,  1)
   " Valid keys and dates at start of line
   AssertEqual 'TodoKey',          SyntaxAt(11,  1)
   AssertEqual 'TodoDate',         SyntaxAt(11,  5)
@@ -165,24 +165,24 @@ Execute (Syntax for invalid or misleading tasks):
   " Invalid date formats.
   " FIXME: Not all cases are tested, not sure how strict to be
   " AssertEqual '',                 SyntaxAt(16, 15)  " FIXME
-  AssertEqual '',                 SyntaxAt(16, 24)
+  AssertEqual 'TodoTodo',         SyntaxAt(16, 24)
   " AssertEqual '',                 SyntaxAt(16, 33)  " FIXME
-  AssertEqual '',                 SyntaxAt(16, 42)
-  AssertEqual '',                 SyntaxAt(16, 44)
-  AssertEqual '',                 SyntaxAt(16, 55)
+  AssertEqual 'TodoTodo',         SyntaxAt(16, 42)
+  AssertEqual 'TodoTodo',         SyntaxAt(16, 44)
+  AssertEqual 'TodoTodo',         SyntaxAt(16, 55)
   " AssertEqual '',                 SyntaxAt(16, 64)  " FIXME
-  AssertEqual '',                 SyntaxAt(16, 78)
+  AssertEqual 'TodoTodo',         SyntaxAt(16, 78)
   " Contexts and projects on the start of a line (valid)
   AssertEqual 'TodoContext',      SyntaxAt(17,  1)
   AssertEqual 'TodoProject',      SyntaxAt(18,  1)
   " Invalid keys, etc
-  AssertEqual '',                 SyntaxAt(19,  5)
-  AssertEqual '',                 SyntaxAt(19, 55)
-  AssertEqual '',                 SyntaxAt(20,  1)
+  AssertEqual 'TodoTodo',         SyntaxAt(19,  5)
+  AssertEqual 'TodoTodo',         SyntaxAt(19, 55)
+  AssertEqual 'TodoTodo',         SyntaxAt(20,  1)
   AssertEqual 'TodoKey',          SyntaxAt(20, 34)
   AssertEqual 'TodoDate',         SyntaxAt(20, 41)
-  AssertEqual '',                 SyntaxAt(20, 55)
-  AssertEqual '',                 SyntaxAt(20, 69)
+  AssertEqual 'TodoTodo',         SyntaxAt(20, 55)
+  AssertEqual 'TodoTodo',         SyntaxAt(20, 69)
 Do (Insert a task due today):
   OTask due-\<BS>:\<C-R>=strftime("%Y-%m-%d")\<CR> today\<C-O>
 Then (Syntax for task due today):