Allow shader params with empty brace inits:

    type myarray[] = {},
    mystruct S = {}

Un-lengthed arrays, if they aren't connected or given a concrete
instance value, still default to length 1 (we don't allow 0-length
arrays, that's a whole other can of worms), but this is now treated as
equivalent to `= { default_value }` (0 for int or float, "" for string).

And it works for structs, too, just means to initialize all the elements
to is obvious (0, "") default values.

It's syntactic sugar, but it removes some clutter for people who want to
have shader parameters that are arrays of undetermined length (and thus
are probably expected to have a runtime-assigned instance value or be
conntected to an output of an earlier layer within the shader group),
removes the requirement for spelling out an initializing value that
won't be used anyway.

src/liboslcomp/codegen.cpp

@@ -960,7 +960,7 @@ ASTNode::codegen_initlist (ref init, TypeSpec type, Symbol *sym)
                 break;
             }
         }
-        if (all_const) {
+        if (all_const && init) {
             std::vector<char> arrayvals (type.simpletype().size());
             for (int i = 0;  init;  init = init->next(), ++i) {
                 ASTliteral *lit = (ASTliteral *)init.get();

src/liboslcomp/oslgram.y

@@ -498,6 +498,16 @@ compound_initializer
                     $$ = new ASTcompound_initializer (oslcompiler, $2);
                     $$->sourceline (@1.first_line);
                 }
+        | '{' '}'
+                {
+                    if (!oslcompiler->declaring_shader_formals())
+                        oslcompiler->error (oslcompiler->filename(),
+                                            oslcompiler->lineno(),
+                                            "Empty compound initializers '{ }' "
+                                            "only allowed for shader parameters.");
+                    $$ = new ASTcompound_initializer (oslcompiler, nullptr);
+                    $$->sourceline (@1.first_line);
+                }
         ;
 
 init_expression_list

src/liboslcomp/typecheck.cpp

@@ -111,6 +111,8 @@ ASTvariable_declaration::typecheck (TypeSpec expected)
         ASSERT (! init->nextptr() &&
                 "compound_initializer should be the only initializer");
         init = ((ASTcompound_initializer *)init.get())->initlist();
+        if (!init)
+            return m_typespec;
     }
 
     // Warning to catch confusing comma operator in variable initializers.
@@ -812,6 +814,8 @@ class ASTcompound_initializer::TypeAdjuster {
     // Adjust the type for every element of an array
     void
     typecheck_array(ASTcompound_initializer* init, TypeSpec expected) {
+        if (! init->initlist())
+            return;    // early out for empty initializer { }
         ASSERT (expected.is_array());
         // Every element of the array is the same type
         TypeSpec elemtype = expected.elementtype();
@@ -936,8 +940,8 @@ class ASTcompound_initializer::TypeAdjuster {
 
     TypeSpec type() const {
         // If succeeded, root type is at end of m_adjust
-        return (m_success || m_debug_successful) ? std::get<1>(m_adjust.back())
-                                                 : TypeSpec(TypeDesc::NONE);
+        return (m_success || m_debug_successful) && m_adjust.size()
+            ? std::get<1>(m_adjust.back()) : TypeSpec(TypeDesc::NONE);
     }
 
     bool success() const { return m_success; }

testsuite/oslc-err-initlist-return/ref/out.txt

@@ -4,5 +4,9 @@ test.osl:14: warning: Function 'struct bcolor badreturn ()' redefined in the sam
   Previous definitions:
     test.osl:13
 test.osl:14: error: Cannot return a 'struct acolor' from 'struct bcolor badreturn()'
-test.osl:17: error: Syntax error: syntax error
+test.osl:17: error: Empty compound initializers '{ }' only allowed for shader parameters.
+test.osl:17: warning: Function 'struct bcolor badreturn ()' redefined in the same scope
+  Previous definitions:
+    test.osl:14
+    test.osl:13
 FAILED test.osl

testsuite/struct/ref/out.txt

@@ -5,6 +5,7 @@ a == { 3.14159, 42, [0 1 2], foobar }
 constructed x == { 6.28319, 21, [1 2 3], constructed }
 
 struct param:  aparam == { 1, 0, [3 4 5], foo! }
+Default init eparam == { 0 0 0, 0 }
 
 after c=a, c == { 3.14159, 42, [0 1 2], foobar }
 
@@ -32,6 +33,7 @@ a == { 3.14159, 42, [0 1 2], foobar }
 constructed x == { 6.28319, 21, [1 2 3], constructed }
 
 struct param:  aparam == { 1, 0, [3 4 5], foo! }
+Default init eparam == { 0 0 0, 0 }
 
 after c=a, c == { 3.14159, 42, [0 1 2], foobar }
 
@@ -59,6 +61,7 @@ a == { 3.14159, 42, [0 1 2], foobar }
 constructed x == { 6.28319, 21, [1 2 3], constructed }
 
 struct param:  aparam == { 1, 0, [3 4 5], foo! }
+Default init eparam == { 0 0 0, 0 }
 
 after c=a, c == { 3.14159, 42, [0 1 2], foobar }
 
@@ -86,6 +89,7 @@ a == { 3.14159, 42, [0 1 2], foobar }
 constructed x == { 6.28319, 21, [1 2 3], constructed }
 
 struct param:  aparam == { 1, 0, [3 4 5], foo! }
+Default init eparam == { 0 0 0, 0 }
 
 after c=a, c == { 3.14159, 42, [0 1 2], foobar }
 

testsuite/struct/test.osl

@@ -36,7 +36,8 @@ void func_with_struct_output_param (output Astruct ap)
 
 shader
 test (
-    Astruct aparam = { 1.0, 0, point(3,4,5), "foo!" }
+    Astruct aparam = { 1.0, 0, point(3,4,5), "foo!" },
+    Bstruct eparam = {}
 )
 {
     printf ("test struct\n");
@@ -65,6 +66,9 @@ test (
     printf ("struct param:  aparam == { %g, %i, [%g], %s }\n",
             aparam.f, aparam.i, aparam.p, aparam.s);
 
+    // Test that empty default initializer for eparam
+    printf ("Default init eparam == { %g, %g }\n", eparam.v, eparam.i);
+
     Bstruct b;
 
     // Structure assignment

testsuite/vararray-default/ref/out.txt

@@ -6,4 +6,6 @@ a array length 3
 b array length 2
   [0] = (9 9 9)
   [1] = (1 2.3 4)
+c array length 1
+  [0] = (0 0 0)
 

testsuite/vararray-default/test.osl

@@ -12,8 +12,11 @@ void print_array_contents (string name, vector v[])
         printf ("  [%d] = (%g)\n", i, v[i]);
 }
 
-shader test (float a[] = {0,1,2.3}, vector b[] = {9, vector(1,2.3,4)})
+shader test (float a[] = {0,1,2.3},
+             vector b[] = {9, vector(1,2.3,4)},
+             vector c[] = {})
 {
     print_array_contents ("a", a);
     print_array_contents ("b", b);
+    print_array_contents ("c", c);
 }