[Runner] Prevent CCACHE env var from affecting compiler wrappers (#406)

Author: giordano

src/Runner.jl

@@ -319,13 +319,16 @@ function generate_compiler_wrappers!(platform::AbstractPlatform; bin_path::Abstr
 
         if allow_ccache
             write(io, """
+            # Override `\${CCACHE}` setting from the outside.
+            CCACHE=""
             if [[ \${USE_CCACHE} == "true" ]]; then
                 CCACHE="ccache"
             fi
             """)
         end
+        # Don't evaluate `${CCACHE}` at all if not allowed in the first place.
         write(io, """
-        vrun \${CCACHE} $(prog) "\${PRE_FLAGS[@]}" "\${ARGS[@]}" "\${POST_FLAGS[@]}"
+        vrun $(allow_ccache ? "\${CCACHE} " : "")$(prog) "\${PRE_FLAGS[@]}" "\${ARGS[@]}" "\${POST_FLAGS[@]}"
         """)
     end
 

test/runners.jl

@@ -177,6 +177,9 @@ end
             """
             test_script = """
                 set -e
+                # Make sure setting `CCACHE` doesn't affect the compiler wrappers.
+                export CCACHE=pwned
+                export USE_CCACHE=false
                 echo '$(test_c)' > test.c
                 echo '$(main_c)' > main.c
                 # Build object file
@@ -222,6 +225,9 @@ end
                 set -e
                 echo '$(test_cpp)' > test.cpp
                 echo '$(main_cpp)' > main.cpp
+                # Make sure setting `CCACHE` doesn't affect the compiler wrappers.
+                export CCACHE=pwned
+                export USE_CCACHE=true
                 # Build object file
                 $(compiler) $(needfpic) -Werror -std=c++11 -c test.cpp -o test.o
                 # Link shared library