From e222cbabb84b5a6357242e47196f7e0eeb69a44f Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Wed, 20 May 2020 15:00:09 +0200
Subject: Implement build script variable hashing

---
 libbuild2/build/script/parser.cxx | 40 ++++++++++++++++++++++++++++++++++++---
 libbuild2/build/script/script.hxx | 14 +++++++++++++-
 2 files changed, 50 insertions(+), 4 deletions(-)

(limited to 'libbuild2/build')

diff --git a/libbuild2/build/script/parser.cxx b/libbuild2/build/script/parser.cxx
index 6649777..86019ba 100644
--- a/libbuild2/build/script/parser.cxx
+++ b/libbuild2/build/script/parser.cxx
@@ -16,6 +16,12 @@ namespace build2
     {
       using type = token_type;
 
+      static inline bool
+      special_variable (const string& name)
+      {
+        return name == ">" || name == "<";
+      }
+
       //
       // Pre-parse.
       //
@@ -96,9 +102,9 @@ namespace build2
         case line_type::var:
           {
             // Check if we are trying to modify any of the special variables
-            // ($>).
+            // ($>, $<).
             //
-            if (t.value == ">")
+            if (special_variable (t.value))
               fail (t) << "attempt to set '" << t.value << "' variable";
 
             // We don't pre-enter variables.
@@ -327,13 +333,41 @@ namespace build2
       lookup parser::
       lookup_variable (name&& qual, string&& name, const location& loc)
       {
+        // In the pre-parse mode collect the referenced variable names for the
+        // script semantics change tracking.
+        //
         if (pre_parse_)
+        {
+          // Add the variable name skipping special variables and suppressing
+          // duplicates.
+          //
+          if (!name.empty () && !special_variable (name))
+          {
+            auto& vars (script_->vars);
+
+            if (find (vars.begin (), vars.end (), name) == vars.end ())
+              vars.push_back (move (name));
+          }
+
           return lookup ();
+        }
 
         if (!qual.empty ())
           fail (loc) << "qualified variable name";
 
-        return environment_->lookup (name);
+        lookup r (environment_->lookup (name));
+
+        // Fail if non-script-local variable with an untracked name.
+        //
+        if (r.defined () && !r.belongs (*environment_))
+        {
+          const auto& vars (script_->vars);
+
+          if (find (vars.begin (), vars.end (), name) == vars.end ())
+            fail (loc) << "use of untracked variable '" << name << "'";
+        }
+
+        return r;
       }
     }
   }
diff --git a/libbuild2/build/script/script.hxx b/libbuild2/build/script/script.hxx
index 1540ed8..29d62aa 100644
--- a/libbuild2/build/script/script.hxx
+++ b/libbuild2/build/script/script.hxx
@@ -40,7 +40,19 @@ namespace build2
         // Note that the variables are not pre-entered into a pool during the
         // parsing phase, so the line variable pointers are NULL.
         //
-        build2::script::lines lines;
+        build2::script::lines   lines;
+
+        // Referenced ordinary (non-special) variables.
+        //
+        // Used for the script semantics change tracking. The variable list is
+        // filled during the pre-parsing phase and is checked against during
+        // the execution phase. If during execution some non-script-local
+        // variable is not found in the list (may happen for a computed name),
+        // then the execution fails since the script semantics may not be
+        // properly tracked (the variable value change will not trigger the
+        // target rebuild).
+        //
+        small_vector<string, 1> vars;
 
         location start_loc;
         location end_loc;
-- 
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