[gtksourceview] cmake.lang: add highlighting for environment variable references

[Sébastien Wilmet <swilmet src gnome org>]

commit c67b8691a54a44fc11b7785f6461d8ceb54ec6c5
Author: Роман Донченко <dpb corrigendum ru>
Date:   Sun Nov 12 18:41:09 2017 +0300

    cmake.lang: add highlighting for environment variable references
    
    The syntax is nearly the same as for regular variable references, and
    I would've just merged the contexts, but builtin variable names have
    no special meaning in environment variable references, so I opted to
    use a separate context to implement that distinction.
    
    There are actually special environment variable names that CMake
    recognizes, but I haven't implemented support for them.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=790345

 data/language-specs/cmake.lang |   17 +++++++++++++++++
 1 files changed, 17 insertions(+), 0 deletions(-)
---
diff --git a/data/language-specs/cmake.lang b/data/language-specs/cmake.lang
index 53fdc6d..71dba4d 100644
--- a/data/language-specs/cmake.lang
+++ b/data/language-specs/cmake.lang
@@ -704,6 +704,21 @@
         <context sub-pattern="0" where="end" style-ref="def:special-char"/>
         <context ref="builtin-variable"/>
         <context ref="variable-reference"/>
+        <context ref="env-variable-reference"/>
+        <context ref="escape-sequence"/>
+        <context ref="disallowed-variable-reference-char"/>
+      </include>
+    </context>
+
+    <context id="env-variable-reference" style-ref="variable"
+             style-inside="true" end-at-line-end="true">
+      <start>\$ENV\{</start>
+      <end>\}</end>
+      <include>
+        <context sub-pattern="0" where="start" style-ref="def:special-char"/>
+        <context sub-pattern="0" where="end" style-ref="def:special-char"/>
+        <context ref="variable-reference"/>
+        <context ref="env-variable-reference"/>
         <context ref="escape-sequence"/>
         <context ref="disallowed-variable-reference-char"/>
       </include>
@@ -716,6 +731,7 @@
         <context sub-pattern="1" where="start" style-ref="builtin-command"/>
         <context sub-pattern="2" where="start" style-ref="variable"/>
         <context ref="variable-reference"/>
+        <context ref="env-variable-reference"/>
         <context ref="constant"/>
         <context ref="def:shell-like-comment"/>
       </include>
@@ -724,6 +740,7 @@
     <context id="cmake">
       <include>
         <context ref="variable-reference"/>
+        <context ref="env-variable-reference"/>
         <context ref="variable-assignment"/>
         <context ref="def:shell-like-comment"/>
         <context ref="constant"/>