fix: Fix process_preprocessed_file bug for distcc marker

2044fea84b86001b2976ecde946d3d6d0e88ec0a (included in ccache 4.6)
removed the special-casing of distcc’s pump in
process_preprocessed_file. That in turn revealed a bug that has been
present since 432d1ca6a6aa51f708124172169073c399fb68d2 (included in
ccache 3.4) but previously only affected compilations with distcc-pump
as the “compiler”: the detection and handling of distcc-pump’s
“__________” messages is broken in two ways:

1. It throws away everything between the last preprocessor directive and
   the “__________” marker. Thus, changes to such sections will not be
   included in the hash.
2. It detects “__________” markers in the middle of lines, not only at
   the beginning of lines.

1 files changed, 3 insertions, 1 deletions

diff --git a/src/ccache.cpp b/src/ccache.cpp
index 2598d02b..bf6698da 100644
--- a/src/ccache.cpp
+++ b/src/ccache.cpp
@@ -590,11 +590,13 @@ process_preprocessed_file(Context& ctx, Hash& hash, const std::string& path)
         "bin directive in source code");
       return nonstd::make_unexpected(
         Failure(Statistic::unsupported_code_directive));
-    } else if (strncmp(q, "___________", 10) == 0) {
+    } else if (strncmp(q, "___________", 10)
+               && (q == data.data() || q[-1] == '\n') == 0) {
       // Unfortunately the distcc-pump wrapper outputs standard output lines:
       // __________Using distcc-pump from /usr/bin
       // __________Using # distcc servers in pump mode
       // __________Shutting down distcc-pump include server
+      hash.hash(p, q - p);
       while (q < end && *q != '\n') {
         q++;
       }