Support for [[@LINE]], [[@LINE+<offset>]], [[@LINE-<offset>]] expressions in
FileCheck.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@167978 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/docs/CommandGuide/FileCheck.rst b/docs/CommandGuide/FileCheck.rst
index 049e10b..ba2fe4a 100644
--- a/docs/CommandGuide/FileCheck.rst
+++ b/docs/CommandGuide/FileCheck.rst
@@ -252,3 +252,30 @@
matches, this allows you to define two separate "``CHECK``" lines that match on
the same line.
+
+FileCheck Expressions
+~~~~~~~~~~~~~~~~~~~~~
+
+
+Sometimes there's a need to verify output which refers line numbers of the match
+file, e.g. when testing compiler diagnostics. This introduces a certain
+fragility of the match file structure, as CHECK: lines contain absolute line
+numbers in the same file, which have to be updated whenever line numbers change
+due to text addition or deletion.
+
+To support this case, FileCheck allows using ``[[@LINE]]``,
+``[[@LINE+<offset>]]``, ``[[@LINE-<offset>]]`` expressions in patterns. These
+expressions expand to a number of the line where a pattern is located (with an
+optional integer offset).
+
+This way match patterns can be put near the relevant test lines and include
+relative line number references, for example:
+
+.. code-block:: c++
+
+ // CHECK: test.cpp:[[@LINE+4]]:6: error: expected ';' after top level declarator
+ // CHECK-NEXT: {{^int a}}
+ // CHECK-NEXT: {{^ \^}}
+ // CHECK-NEXT: {{^ ;}}
+ int a
+