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-rw-r--r--libbuild2/parser.cxx79
1 files changed, 52 insertions, 27 deletions
diff --git a/libbuild2/parser.cxx b/libbuild2/parser.cxx
index 00366e6..d288bf2 100644
--- a/libbuild2/parser.cxx
+++ b/libbuild2/parser.cxx
@@ -2590,21 +2590,6 @@ namespace build2
return;
}
- // What should we do if there are no prerequisites (for example, because
- // of an empty wildcard result)? We can fail or we can ignore. In most
- // cases, however, this is probably an error (for example, forgetting to
- // checkout a git submodule) so let's not confuse the user and fail (one
- // can always handle the optional prerequisites case with a variable and
- // an if).
- //
- if (pns.empty ())
- fail (ploc) << "no prerequisites in dependency chain or prerequisite-"
- << "specific variable assignment";
-
- next_with_attributes (t, tt); // Recognize attributes after `:`.
-
- auto at (attributes_push (t, tt));
-
// If we are here, then this can be one of three things:
//
// 1. A prerequisite-specific variable bloc:
@@ -2618,10 +2603,37 @@ namespace build2
//
// foo: bar: x = y
//
- // 3. A further dependency chain :
+ // 3. A further dependency chain:
//
// foo: bar: baz ...
//
+ // What should we do if there are no prerequisites, for example, because
+ // of an empty wildcard result or empty variable expansion? We can fail or
+ // we can ignore. In most cases, however, this is probably an error (for
+ // example, forgetting to checkout a git submodule) so let's not confuse
+ // the user and fail (one can always handle the optional prerequisites
+ // case with a variable and an if).
+ //
+ // On the other hand, we allow just empty prerequisites (which is also the
+ // more common case by far) and so it's strange that we don't allow the
+ // same with, say, `include = false`:
+ //
+ // exe{foo}: cxx{$empty} # Ok.
+ // exe{foo}: cxx{$empty}: include = false # Not Ok?
+ //
+ // So let's ignore in the first two cases (variable block and assignment)
+ // for consistency. The dependency chain is iffy both conceptually and
+ // implementation-wise (it could be followed by a variable block). So
+ // let's keep it an error for now.
+ //
+ // Note that the syntactically-empty prerequisite list is still an error:
+ //
+ // exe{foo}: : include = false # Error.
+ //
+ next_with_attributes (t, tt); // Recognize attributes after `:`.
+
+ auto at (attributes_push (t, tt));
+
if (tt == type::newline || tt == type::eos)
{
attributes_pop (); // Must be none since can't be standalone.
@@ -2636,15 +2648,22 @@ namespace build2
// Parse the block for each prerequisites of each target.
//
- for_each_p ([this] (token& t, token_type& tt)
- {
- next (t, tt); // First token inside the block.
+ if (!pns.empty ())
+ for_each_p ([this] (token& t, token_type& tt)
+ {
+ next (t, tt); // First token inside the block.
- parse_variable_block (t, tt);
+ parse_variable_block (t, tt);
- if (tt != type::rcbrace)
- fail (t) << "expected '}' instead of " << t;
- });
+ if (tt != type::rcbrace)
+ fail (t) << "expected '}' instead of " << t;
+ });
+ else
+ {
+ skip_block (t, tt);
+ if (tt != type::rcbrace)
+ fail (t) << "expected '}' instead of " << t;
+ }
next (t, tt); // Presumably newline after '}'.
next_after_newline (t, tt, '}'); // Should be on its own line.
@@ -2667,10 +2686,13 @@ namespace build2
// Parse the assignment for each prerequisites of each target.
//
- for_each_p ([this, &var, at] (token& t, token_type& tt)
- {
- parse_variable (t, tt, var, at);
- });
+ if (!pns.empty ())
+ for_each_p ([this, &var, at] (token& t, token_type& tt)
+ {
+ parse_variable (t, tt, var, at);
+ });
+ else
+ skip_line (t, tt);
next_after_newline (t, tt);
@@ -2689,6 +2711,9 @@ namespace build2
//
else
{
+ if (pns.empty ())
+ fail (ploc) << "no prerequisites in dependency chain";
+
// @@ This is actually ambiguous: prerequisite or target attributes
// (or both or neither)? Perhaps this should be prerequisites for
// the same reason as below (these are prerequsites first).