Update make variables documentation:

- Remove outdated warning about C++ variables and "bazel --show_make_env"
- Clarify what "execroot" means for source vs. output files
- Make the genrule example more readable

PiperOrigin-RevId: 231459264

src/main/java/com/google/devtools/build/docgen/templates/be/make-variables.vm

diff --git a/src/main/java/com/google/devtools/build/docgen/templates/be/make-variables.vm b/src/main/java/com/google/devtools/build/docgen/templates/be/make-variables.vm
index 816d17b..96d604a 100644
--- a/src/main/java/com/google/devtools/build/docgen/templates/be/make-variables.vm
+++ b/src/main/java/com/google/devtools/build/docgen/templates/be/make-variables.vm
@@ -97,13 +97,6 @@
   and look at the top output lines with capital letters.
 </p>
 
-<p>
-  <b>Nov 7, 2018</b>: C++ variables appear in the predefined list unless
-  <code><a
-  href="https://github.com/bazelbuild/bazel/issues/6381">--incompatible_disable_cc_configuration_make_variables</a></code>
-  is set. They will no longer appear after this flag is removed.
-</p>
-
 <p><strong>Toolchain option variables</strong></p>
 
 <ul><!--  keep alphabetically sorted  -->
@@ -206,12 +199,14 @@
 <p>
   The predefined variables <code>execpath</code>, <code>execpaths</code>,
   <code>rootpath</code>, <code>rootpaths</code>, <code>location</code>, and
-  <code>locations</code> take a label parameter (e.g. <code>$(execpath
+  <code>locations</code> take label parameters (e.g. <code>$(execpath
   //foo:bar)</code>) and substitute the file paths denoted by that label.
 </p>
 <p>
-  For source files, this is the path of the file. For other rules, this is the
-  output path(s) of the file(s) generated by that rule.
+
+  For source files, this is the path relative to your workspace root.
+  For files that are outputs of rules, this is the file's <i>output path</i>
+  (see the explanation of <i>output files</i> below).
 </p>
 
 <p>Example:</p>
@@ -228,15 +223,17 @@
   name = "show_app_output",
   srcs = ["empty.source"],
   outs = ["app_output"],
-  cmd = "echo :app output paths > $@;"
-  + "echo ' ' execpath: $(execpath :app) >> $@;"
-  + "echo ' ' runfiles: $(rootpath :app) >> $@;"
-  + "echo ' ' location: $(location :app) >> $@;"
-  + "echo >> $@;"
-  + "echo source file paths >> $@;"
-  + "echo ' ' execpath: $(execpath empty.source) >> $@;"
-  + "echo ' ' runfiles: $(rootpath empty.source) >> $@",
-  + "echo ' ' location: $(location empty.source) >> $@;"
+  cmd = """cat <<EOF > $@
+:app output paths
+ execpath: $(execpath :app)
+ runfiles: $(rootpath :app)
+ location: $(location :app)
+
+source file paths
+ execpath: $(execpath empty.source)
+ runfiles: $(rootpath empty.source)
+ location: $(location empty.source)
+EOF""",
   tools = [":app"])
 
 $ bazel build //testapp:show_app_output && cat bazel-genfiles/testapp/app_output
@@ -258,9 +255,10 @@
 <ul>
   <li>
     <p>
-      <code>execpath</code>:  Denotes the path beneath the <a
-      href="../output_directories.html">execroot</a> where Bazel runs build
-      actions.
+      <code>execpath</code>:  Denotes the path beneath the
+
+      <a href="../output_directories.html">execroot</a>
+    where Bazel runs build actions.
     </p>
     <p>
       In the above example, Bazel runs all build actions in the directory linked