Keep mtime check always enabled on Windows

Windows is known not to guarantee monotonically increasing mtimes.

4 files changed, 16 insertions, 9 deletions

diff --git a/build2/b-options.cxx b/build2/b-options.cxx
index 182dfb0..1c59231 100644
--- a/build2/b-options.cxx
+++ b/build2/b-options.cxx
@@ -1226,11 +1226,14 @@ namespace build2
     os << std::endl
        << "\033[1m--mtime-check\033[0m         Perform file modification time sanity checks. These" << ::std::endl
        << "                      checks can be helpful in diagnosing spurious rebuilds and" << ::std::endl
-       << "                      are enabled by default for the staged version of the" << ::std::endl
-       << "                      build system. Use \033[1m--no-mtime-check\033[0m to disable." << ::std::endl;
+       << "                      are enabled by default on Windows (which is known not to" << ::std::endl
+       << "                      guarantee monotonically increasing mtimes) and for the" << ::std::endl
+       << "                      staged version of the build system on other platforms." << ::std::endl
+       << "                      Use \033[1m--no-mtime-check\033[0m to disable." << ::std::endl;
 
     os << std::endl
-       << "\033[1m--no-mtime-check\033[0m      Don't perform file modification time sanity checks." << ::std::endl;
+       << "\033[1m--no-mtime-check\033[0m      Don't perform file modification time sanity checks. See" << ::std::endl
+       << "                      \033[1m--mtime-check\033[0m for details." << ::std::endl;
 
     os << std::endl
        << "\033[1m--no-column\033[0m           Don't print column numbers in diagnostics." << ::std::endl;
diff --git a/build2/b.cli b/build2/b.cli
index 0ce0f9e..112db2b 100644
--- a/build2/b.cli
+++ b/build2/b.cli
@@ -580,13 +580,15 @@ namespace build2
     {
       "Perform file modification time sanity checks. These checks can be
        helpful in diagnosing spurious rebuilds and are enabled by default
-       for the staged version of the build system. Use \cb{--no-mtime-check}
-       to disable."
+       on Windows (which is known not to guarantee monotonically increasing
+       mtimes) and for the staged version of the build system on other
+       platforms. Use \cb{--no-mtime-check} to disable."
     }
 
     bool --no-mtime-check
     {
-      "Don't perform file modification time sanity checks."
+      "Don't perform file modification time sanity checks. See
+       \cb{--mtime-check} for details."
     }
 
     bool --no-column
diff --git a/libbuild2/config.hxx.in b/libbuild2/config.hxx.in
index 59917db..9a2e01f 100644
--- a/libbuild2/config.hxx.in
+++ b/libbuild2/config.hxx.in
@@ -21,9 +21,11 @@
 #define LIBBUILD2_STAGE true
 
 // Modification time sanity checks are by default only enabled for the staged
-// version but this can be overridden at runtime with --[no-]mtime-check.
+// version unless we are on Windows (which is known not to guarantee
+// monotonically increasing mtimes). But this can be overridden at runtime
+// with --[no-]mtime-check.
 //
-#if LIBBUILD2_STAGE
+#if LIBBUILD2_STAGE || defined(_WIN32)
 #  define LIBBUILD2_MTIME_CHECK true
 #else
 #  define LIBBUILD2_MTIME_CHECK false
diff --git a/libbuild2/depdb.hxx b/libbuild2/depdb.hxx
index abc2565..671c7fd 100644
--- a/libbuild2/depdb.hxx
+++ b/libbuild2/depdb.hxx
@@ -128,7 +128,7 @@ namespace build2
     // Note that it would also be good to compare the target timestamp against
     // the newest prerequisite. However, obtaining this information would cost
     // extra (see execute_prerequisites()). So maybe later, if we get a case
-    // where this is a problem (in a sense, the database is a buffer between
+    // where this is a problem (in a sense, the database is a barrier between
     // prerequisites and the target).
     //
     void