syntax: correctly highlight paths with interpolation

default.nix

@@ -39,6 +39,9 @@ stdenv.mkDerivation rec {
     endfunction
 
     command! Syntax call Syntax()
+
+    set backspace=2
+    set hlsearch
   '';
 
   checkPhase = ''

syntax/nix.vim

@@ -50,6 +50,7 @@ syn region nixString matchgroup=nixStringDelimiter start=+''+ skip=+''['$\\]+ en
 syn match nixFunctionCall "[a-zA-Z_][a-zA-Z0-9_'-]*"
 
 syn match nixPath "[a-zA-Z0-9._+-]*\%(/[a-zA-Z0-9._+-]\+\)\+"
+syn region nixInterpolatedPath start="\%(\~\|[a-zA-Z0-9._+-]*\)/[a-zA-Z0-9._+/-]*\ze${" skip="[a-zA-Z0-9._+/-]*\ze${" end="}\@<=[a-zA-Z0-9._+/-]*\%([^a-zA-Z0-9._+/-]\|$\)\@=" contains=nixInterpolation
 syn match nixHomePath "\~\%(/[a-zA-Z0-9._+-]\+\)\+"
 syn match nixSearchPath "[a-zA-Z0-9._+-]\+\%(\/[a-zA-Z0-9._+-]\+\)*" contained
 syn match nixPathDelimiter "[<>]" contained
@@ -123,7 +124,7 @@ syn region nixWithExpr matchgroup=nixWithExprKeyword start="\<with\>" matchgroup
 
 syn region nixAssertExpr matchgroup=nixAssertKeyword start="\<assert\>" matchgroup=NONE end=";" contains=@nixExpr
 
-syn cluster nixExpr contains=nixBoolean,nixNull,nixOperator,nixParen,nixInteger,nixRecKeyword,nixConditional,nixBuiltin,nixSimpleBuiltin,nixComment,nixFunctionCall,nixFunctionArgument,nixArgOperator,nixSimpleFunctionArgument,nixPath,nixHomePath,nixSearchPathRef,nixURI,nixAttributeSet,nixList,nixSimpleString,nixString,nixLetExpr,nixIfExpr,nixWithExpr,nixAssertExpr,nixInterpolation
+syn cluster nixExpr contains=nixBoolean,nixNull,nixOperator,nixParen,nixInteger,nixRecKeyword,nixConditional,nixBuiltin,nixSimpleBuiltin,nixComment,nixFunctionCall,nixFunctionArgument,nixArgOperator,nixSimpleFunctionArgument,nixInterpolatedPath,nixPath,nixHomePath,nixSearchPathRef,nixURI,nixAttributeSet,nixList,nixSimpleString,nixString,nixLetExpr,nixIfExpr,nixWithExpr,nixAssertExpr,nixInterpolation
 
 " These definitions override @nixExpr and have to come afterwards:
 
@@ -179,6 +180,7 @@ hi def link nixNamespacedBuiltin         Special
 hi def link nixNull                      Constant
 hi def link nixOperator                  Operator
 hi def link nixPath                      Include
+hi def link nixInterpolatedPath          nixPath
 hi def link nixPathDelimiter             Delimiter
 hi def link nixRecKeyword                Keyword
 hi def link nixSearchPath                Include

test/nix.vader

@@ -234,6 +234,179 @@ Execute (syntax):
   AssertEqual SyntaxOf('\./\.'), 'nixPath'
   AssertEqual SyntaxOf('/etc/passwd'), 'nixPath'
 
+Given nix (path-with-interpolation-simple):
+  ./snens/${bar}/baz
+
+Execute (syntax):
+  AssertEqual SyntaxOf('./'), 'nixInterpolatedPath'
+  AssertEqual SyntaxOf('${'), 'nixInterpolationDelimiter'
+  AssertEqual SyntaxOf('/baz'), 'nixInterpolatedPath'
+  AssertEqual SyntaxAt(1, 8), 'nixInterpolatedPath'
+  AssertEqual SyntaxAt(1, 15), 'nixInterpolatedPath'
+
+Given nix (path-with-interpolation-in-path-part):
+  ./snens/${bar}kek/end
+
+Execute (syntax):
+  AssertEqual SyntaxOf('./'), 'nixInterpolatedPath'
+  AssertEqual SyntaxOf('${'), 'nixInterpolationDelimiter'
+  AssertEqual SyntaxOf('/end'), 'nixInterpolatedPath'
+  AssertEqual SyntaxAt(1, 8), 'nixInterpolatedPath'
+  AssertEqual SyntaxAt(1, 14), 'nixInterpolationDelimiter'
+  AssertEqual SyntaxAt(1, 15), 'nixInterpolatedPath'
+
+Given nix (path-with-interpolation-and-prefix):
+  ./snens/pre${bar}
+
+Execute (syntax):
+  AssertEqual SyntaxOf('./'), 'nixInterpolatedPath'
+  AssertEqual SyntaxOf('${'), 'nixInterpolationDelimiter'
+  AssertEqual SyntaxAt(1, 8), 'nixInterpolatedPath'
+  AssertEqual SyntaxAt(1, 12), 'nixInterpolationDelimiter'
+  AssertEqual SyntaxAt(1, 17), 'nixInterpolationDelimiter'
+
+Given nix (path-with-interpolation-suffix):
+  ./snens/pre${bar}suff
+
+Execute (syntax):
+  AssertEqual SyntaxOf('./'), 'nixInterpolatedPath'
+  AssertEqual SyntaxOf('${'), 'nixInterpolationDelimiter'
+  AssertEqual SyntaxAt(1, 8), 'nixInterpolatedPath'
+  AssertEqual SyntaxAt(1, 12), 'nixInterpolationDelimiter'
+  AssertEqual SyntaxAt(1, 17), 'nixInterpolationDelimiter'
+  AssertEqual SyntaxOf('suff'), 'nixInterpolatedPath'
+
+Given nix (path-with-interpolation-in-mid-part):
+  ./snens/pre${bar}/kek
+
+Execute (syntax):
+  AssertEqual SyntaxOf('./'), 'nixInterpolatedPath'
+  AssertEqual SyntaxOf('${'), 'nixInterpolationDelimiter'
+  AssertEqual SyntaxOf('/kek'), 'nixInterpolatedPath'
+  AssertEqual SyntaxOf('bar'), 'nixInterpolationParam'
+
+Given nix (path-with-multiple-interpolations):
+  ./snens/${bar}${baz}
+
+Execute (syntax):
+  AssertEqual SyntaxOf('./snens'), 'nixInterpolatedPath'
+  AssertEqual SyntaxAt(1, 9), 'nixInterpolationDelimiter'
+  AssertEqual SyntaxOf('bar'), 'nixInterpolationParam'
+  AssertEqual SyntaxOf('baz'), 'nixInterpolationParam'
+  AssertEqual SyntaxAt(1, 20), 'nixInterpolationDelimiter'
+
+Given nix (path-with-multiple-interpolations-and-infix):
+  ./snens/${bar}in${baz}
+
+Execute (syntax):
+  AssertEqual SyntaxOf('./snens'), 'nixInterpolatedPath'
+  AssertEqual SyntaxAt(1, 9), 'nixInterpolationDelimiter'
+  AssertEqual SyntaxOf('in'), 'nixInterpolatedPath'
+  AssertEqual SyntaxAt(1, 17), 'nixInterpolationDelimiter'
+  AssertEqual SyntaxOf('bar'), 'nixInterpolationParam'
+  AssertEqual SyntaxOf('baz'), 'nixInterpolationParam'
+  AssertEqual SyntaxAt(1, 22), 'nixInterpolationDelimiter'
+  AssertEqual SyntaxAt(1, 14), 'nixInterpolationDelimiter'
+
+Given nix (path-with-multiple-interpolations-and-suffix):
+  ./snens/${bar}in${baz}suff
+  AssertEqual SyntaxOf('./snens'), 'nixInterpolatedPath'
+  AssertEqual SyntaxAt(1, 9), 'nixInterpolationDelimiter'
+  AssertEqual SyntaxOf('in'), 'nixInterpolatedPath'
+  AssertEqual SyntaxAt(1, 17), 'nixInterpolationDelimiter'
+  AssertEqual SyntaxOf('bar'), 'nixInterpolationParam'
+  AssertEqual SyntaxOf('baz'), 'nixInterpolationParam'
+  AssertEqual SyntaxAt(1, 22), 'nixInterpolationDelimiter'
+  AssertEqual SyntaxAt(1, 14), 'nixInterpolationDelimiter'
+  AssertEqual SyntaxOf('suff'), 'nixInterpolatedPath'
+
+Execute (syntax):
+
+Given nix (path-with-multiple-interpolations-and-prefix):
+  ./snens/pre${bar}in${baz}
+
+Execute (syntax):
+  AssertEqual SyntaxOf('./snens'), 'nixInterpolatedPath'
+  AssertEqual SyntaxAt(1, 12), 'nixInterpolationDelimiter'
+  AssertEqual SyntaxOf('in'), 'nixInterpolatedPath'
+  AssertEqual SyntaxAt(1, 20), 'nixInterpolationDelimiter'
+  AssertEqual SyntaxOf('bar'), 'nixInterpolationParam'
+  AssertEqual SyntaxOf('baz'), 'nixInterpolationParam'
+  AssertEqual SyntaxAt(1, 25), 'nixInterpolationDelimiter'
+  AssertEqual SyntaxAt(1, 17), 'nixInterpolationDelimiter'
+
+Given nix (path-with-multiple-interpolations-and-dir-suffix):
+  ./snens/${bar}in${baz}/suff
+
+Execute (syntax):
+  AssertEqual SyntaxOf('./snens'), 'nixInterpolatedPath'
+  AssertEqual SyntaxAt(1, 9), 'nixInterpolationDelimiter'
+  AssertEqual SyntaxOf('in'), 'nixInterpolatedPath'
+  AssertEqual SyntaxAt(1, 17), 'nixInterpolationDelimiter'
+  AssertEqual SyntaxOf('bar'), 'nixInterpolationParam'
+  AssertEqual SyntaxOf('baz'), 'nixInterpolationParam'
+  AssertEqual SyntaxAt(1, 22), 'nixInterpolationDelimiter'
+  AssertEqual SyntaxAt(1, 14), 'nixInterpolationDelimiter'
+  AssertEqual SyntaxAt(1, 23), 'nixInterpolatedPath'
+
+Given nix (path-with-multiple-interpolations-in-separate-dirs):
+  ./snens/${bar}/${baz}
+
+Execute (syntax):
+  AssertEqual SyntaxOf('./snens'), 'nixInterpolatedPath'
+  AssertEqual SyntaxAt(1, 9), 'nixInterpolationDelimiter'
+  AssertEqual SyntaxAt(1, 16), 'nixInterpolationDelimiter'
+  AssertEqual SyntaxOf('bar'), 'nixInterpolationParam'
+  AssertEqual SyntaxOf('baz'), 'nixInterpolationParam'
+  AssertEqual SyntaxAt(1, 21), 'nixInterpolationDelimiter'
+  AssertEqual SyntaxAt(1, 14), 'nixInterpolationDelimiter'
+  AssertEqual SyntaxAt(1, 15), 'nixInterpolatedPath'
+
+Given nix (homepath-with-interpolation):
+  ~/${snens}
+
+Execute (syntax):
+  AssertEqual SyntaxOf('\~/'), 'nixInterpolatedPath'
+  AssertEqual SyntaxOf('${'), 'nixInterpolationDelimiter'
+  AssertEqual SyntaxOf('snens'), 'nixInterpolationParam'
+
+Given nix (path-with-invalid-infix):
+  ./snens/${bar}in!${baz}
+
+Execute (syntax):
+  AssertEqual SyntaxOf('./snens'), 'nixInterpolatedPath'
+  AssertEqual SyntaxAt(1, 8), 'nixInterpolatedPath'
+  AssertEqual SyntaxAt(1, 9), 'nixInterpolationDelimiter'
+  AssertEqual SyntaxOf('bar'), 'nixInterpolationParam'
+  AssertEqual SyntaxOf('in'), 'nixInterpolatedPath'
+# invalid syntax. Just make sure this isn't misinterpreted as a path.
+  AssertEqual SyntaxOf('!'), 'nixOperator'
+  AssertEqual SyntaxAt(1, 18), ''
+  AssertEqual SyntaxOf('baz'), 'nixArgumentDefinition'
+
+Given nix (path-with-recursive-interpolation):
+  ./snens/${bar.${baz}}/suff
+
+Execute (syntax):
+  AssertEqual SyntaxOf('./snens'), 'nixInterpolatedPath'
+  AssertEqual SyntaxAt(1, 9), 'nixInterpolationDelimiter'
+  AssertEqual SyntaxAt(1, 15), 'nixInterpolationDelimiter'
+  AssertEqual SyntaxAt(1, 21), 'nixInterpolationDelimiter'
+  AssertEqual SyntaxAt(1, 11), 'nixInterpolationParam'
+  AssertEqual SyntaxAt(1, 22), 'nixInterpolatedPath'
+
+Given nix (path-with-multiline-subexpr):
+  foo/${
+    "bar"
+  }
+
+Execute (syntax):
+  AssertEqual SyntaxOf('foo/'), 'nixInterpolatedPath'
+  AssertEqual SyntaxOf('${'), 'nixInterpolationDelimiter'
+  AssertEqual SyntaxOf('"'), 'nixStringDelimiter'
+  AssertEqual SyntaxOf('bar'), 'nixSimpleString'
+  AssertEqual SyntaxOf('}'), 'nixInterpolationDelimiter'
+
 Given nix (let):
   let
     foo = true;