runtime(vim): Update base-syntax, contain let-heredocs

Limit heredoc matches to assignment statements.  Matching these at the
top level is very slow.

closes: #17473

Signed-off-by: Doug Kearns <dougkearns@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/syntax/testdir/input/setup/vim9_ex_let_heredoc.vim

@@ -0,0 +1,2 @@
+highlight link vimVar Identifier
+

runtime/syntax/testdir/input/vim9_ex_let_heredoc.vim

@@ -0,0 +1,298 @@
+vim9script
+# VIM_TEST_SETUP let g:vimsyn_folding = "h"
+# VIM_TEST_SETUP setl fdc=2 fdl=99 fdm=syntax
+
+
+var foo =<< END
+line1
+line2
+END
+
+  var foo =<< END
+line1
+line2
+END
+
+var [foo, bar] =<< EOS
+line1
+line2
+EOS
+
+  var [foo, bar] =<< EOS
+line1
+line2
+EOS
+
+var [foo,
+      \ bar] =<< EOS
+line1
+line2
+EOS
+
+  var [foo,
+	\ bar] =<< EOS
+line1
+line2
+EOS
+
+# assignment
+
+foo =<< END
+line1
+line2
+END
+
+  foo =<< END
+line1
+line2
+END
+
+g:foo =<< END
+line1
+line2
+END
+
+  g:foo =<< END
+line1
+line2
+END
+
+[foo, bar] =<< EOS
+line1
+line2
+EOS
+
+  [foo, bar] =<< EOS
+line1
+line2
+EOS
+
+[foo,
+      \ bar] =<< EOS
+line1
+line2
+EOS
+
+  [foo,
+	\ bar] =<< EOS
+line1
+line2
+EOS
+
+[g:foo, g:bar] =<< EOS
+line1
+line2
+EOS
+
+  [g:foo, g:bar] =<< EOS
+line1
+line2
+EOS
+
+[g:foo,
+      \ g:bar] =<< EOS
+line1
+line2
+EOS
+
+  [g:foo,
+	\ g:bar] =<< EOS
+line1
+line2
+EOS
+
+
+# typed
+
+var foo: list<string> =<< END
+line1
+line2
+END
+
+var [foo: string, bar: string] =<< END
+line1
+line2
+END
+
+# assignment
+
+# trim
+
+var foo =<< trim END
+  line1
+  line2
+END
+
+  var foo =<< trim END
+    line1
+    line2
+  END
+
+
+# interpolation
+
+var foo =<< eval END
+line{1 + 0}
+line{1 + 1}
+END
+
+  var foo =<< eval END
+line{1 + 0}
+line{1 + 1}
+END
+
+var foo =<< trim eval END
+  line{1 + 0}
+  line{1 + 1}
+END
+
+  var foo =<< trim eval END
+    line{1 + 0}
+    line{1 + 1}
+  END
+
+# no interpolation (escaped { and })
+
+var foo =<< eval END
+line{{1 + 0}}
+line{{1 + 1}}
+END
+
+  var foo =<< eval END
+line{{1 + 0}}
+line{{1 + 1}}
+END
+
+var foo =<< trim eval END
+  line{{1 + 0}}
+  line{{1 + 1}}
+END
+
+  var foo =<< trim eval END
+    line{{1 + 0}}
+    line{{1 + 1}}
+  END
+
+
+# no interpolation
+
+var foo =<< END
+line{1 + 0}
+line{1 + 1}
+END
+
+  var foo =<< END
+line{1 + 0}
+line{1 + 1}
+END
+
+var foo =<< trim END
+  line{1 + 0}
+  line{1 + 1}
+END
+
+  var foo =<< trim END
+    line{1 + 0}
+    line{1 + 1}
+  END
+
+
+# end marker must not be followed by whitespace
+
+# assert_equal(foo, ["END "])
+var foo =<< END
+END 
+END
+
+# assert_equal(foo, [" END "])
+var foo =<< END
+ END 
+END
+
+# assert_equal(foo, ["END "])
+var foo =<< trim END
+  END 
+END
+
+# assert_equal(foo, ["END "])
+  var foo =<< trim END
+    END 
+  END
+
+
+# end marker must be vertically aligned with :var (if preceded by whitespace)
+
+# assert_equal(foo, ["END"])
+var foo =<< trim END
+  END
+END
+
+  # assert_equal(foo, ["END"])
+  var foo =<< trim END
+    END
+  END
+
+# assert_equal(foo, ["END "])
+var foo =<< trim END
+END 
+END
+
+  # assert_equal(foo, ["END"])
+  var foo =<< trim END
+    END
+  END
+
+  # assert_equal(foo, ["END "])
+  var foo =<< trim END
+    END 
+  END
+
+  # assert_equal(foo, ["END"])
+  var foo =<< trim END
+     END
+  END
+
+  # assert_equal(foo, ["END "])
+  var foo =<< trim END
+     END 
+  END
+
+  # assert_equal(foo, ["END "])
+  var foo =<< trim END
+END 
+END
+
+  # assert_equal(foo, ["END"])
+  var foo =<< trim END
+ END
+END
+
+  # assert_equal(foo, ["END"])
+  var foo =<< trim END
+   END
+END
+
+
+# end markers
+
+var foo =<< !@#$%^&*()_+
+line1
+line2
+!@#$%^&*()_+
+
+var foo =<< 0!@#$%^&*()_+
+line1
+line2
+0!@#$%^&*()_+
+
+var foo =<< A!@#$%^&*()_+
+line1
+line2
+A!@#$%^&*()_+
+
+# error - leading lowercase character
+var foo =<< a!@#$%^&*()_+
+line1
+line2
+a!@#$%^&*()_+
+

runtime/syntax/testdir/input/vim_ex_let_heredoc.vim

@@ -13,6 +13,60 @@ line1
 line2
 END
 
+let [foo, bar] =<< EOS
+line1
+line2
+EOS
+
+  let [foo, bar] =<< EOS
+line1
+line2
+EOS
+
+let [foo,
+      \ bar] =<< EOS
+line1
+line2
+EOS
+
+  let [foo,
+	\ bar] =<< EOS
+line1
+line2
+EOS
+
+let g:foo =<< END
+line1
+line2
+END
+
+  let g:foo =<< END
+line1
+line2
+END
+
+let [g:foo, g:bar] =<< EOS
+line1
+line2
+EOS
+
+  let [g:foo, g:bar] =<< EOS
+line1
+line2
+EOS
+
+let [g:foo,
+      \ g:bar] =<< EOS
+line1
+line2
+EOS
+
+  let [g:foo,
+	\ g:bar] =<< EOS
+line1
+line2
+EOS
+
 
 " trim