Detect and diagnose presence of certain GCC environment variables

Their presence is incompatible with what we are doing.

2 files changed, 14 insertions, 8 deletions

diff --git a/libbuild2/cc/guess.cxx b/libbuild2/cc/guess.cxx
index ff96466..09e14fa 100644
--- a/libbuild2/cc/guess.cxx
+++ b/libbuild2/cc/guess.cxx
@@ -1815,7 +1815,8 @@ namespace build2
 
     // See "Environment Variables Affecting GCC".
     //
-    // @@ TODO: It feels like we should unset the following variables:
+    // Note that we also check below that the following variables are not set
+    // since they would interfere with what we are doing.
     //
     // DEPENDENCIES_OUTPUT
     // SUNPRO_DEPENDENCIES
@@ -2028,6 +2029,12 @@ namespace build2
 
       // Environment.
       //
+      if (getenv ("DEPENDENCIES_OUTPUT"))
+        fail << "GCC DEPENDENCIES_OUTPUT environment variable is set";
+
+      if (getenv ("SUNPRO_DEPENDENCIES"))
+        fail << "GCC SUNPRO_DEPENDENCIES environment variable is set";
+
       const char* const* c_env (nullptr);
       switch (xl)
       {
diff --git a/libbuild2/config/utility.hxx b/libbuild2/config/utility.hxx
index 4673d0c..cec4bc3 100644
--- a/libbuild2/config/utility.hxx
+++ b/libbuild2/config/utility.hxx
@@ -104,13 +104,12 @@ namespace build2
     //
     // 4. Finally, there could be environment variables that are incompatible
     //    with what we are doing (e.g., they change the mode of operation or
-    //    some such; see GCC's DEPENDENCIES_OUTPUT for example). While they
-    //    can be cleared for each invocation, this is burdensome and it is
-    //    often easier to just unset them for the entire build system process
-    //    if we can be reasonable sure that there can be no plausible use for
-    //    this variable (e.g., by another module or by the buildfile
-    //    directly). The module's load() function is a natural place to do
-    //    that.
+    //    some such; see GCC's DEPENDENCIES_OUTPUT for example). The two ways
+    //    to deal with this is either clear them for each invocation or, if
+    //    that's too burdensome and there is no good reason to have the build
+    //    system invoked with such variables, detect their presence and fail.
+    //    Note that unsetting them for the entire build system process is not
+    //    an option since that would be racy.
     //
     // See also build2::hash_environment().
     //