[vala/wip/baedert/nullable: 9/25] nullabilitychecker: Warn on invalid assignments

[Timm Bäder <baedert src gnome org>]

commit fac6e6c0b97e8b9f1463a6040c24f928748d30ba
Author: Timm Bäder <mail baedert org>
Date:   Sat Nov 5 21:05:56 2016 +0100

    nullabilitychecker: Warn on invalid assignments
    
    Assignments from nullable to non-nullable are wrong unless the right
    side is guaranteed to not be null at this point.

 vala/valanullabilitychecker.vala |   82 +++++++++++++++++++------------------
 1 files changed, 42 insertions(+), 40 deletions(-)
---
diff --git a/vala/valanullabilitychecker.vala b/vala/valanullabilitychecker.vala
index 1693145..4c44b31 100644
--- a/vala/valanullabilitychecker.vala
+++ b/vala/valanullabilitychecker.vala
@@ -24,6 +24,22 @@ public class Vala.NullabilityChecker : CodeVisitor {
                this.visit_basic_block (root_block);
        }
 
+       private void get_nullability_state (Symbol symbol, out bool is_null, out bool is_non_null) {
+               is_null = false;
+               is_non_null = false;
+               BasicBlock? b = current_block;
+               while (b != null) {
+                       if (b.null_vars.contains (symbol)) {
+                               is_null = true;
+                               break;
+                       } else if (b.non_null_vars.contains (symbol)) {
+                               is_non_null = true;
+                               break;
+                       }
+                       b = b.parent;
+               }
+       }
+
        private void visit_basic_block (BasicBlock block) {
                if (debug) {
                        message ("Checking Basic Block %s (%d nulls, %d non-nulls)",
@@ -34,41 +50,28 @@ public class Vala.NullabilityChecker : CodeVisitor {
                this.current_block = block;
 
                foreach (var node in block.nodes) {
-                       //message ("Accept() ing %s", node.type_name);
                        node.accept (this);
                }
 
                foreach (var child in block.children) {
                        visit_basic_block (child);
                }
-
-
                // TODO: reset current_block ???
        }
 
        public override void visit_member_access (MemberAccess access) {
                if (debug)
                        message ("Checking Member Access %s", access.to_string ());
-               if (access.inner != null) {
+               if (access.inner != null && access.inner.symbol_reference != null) {
                        if (debug)
                                message ("Inner: %s", access.inner.to_string ());
                        bool is_null = false;
                        bool is_non_null = false;
-                       BasicBlock? b = current_block;
-                       while (b != null) {
-                               if (b.null_vars.contains (access.inner.symbol_reference)) {
-                                       is_null = true;
-                                       break;
-                               } else if (b.non_null_vars.contains (access.inner.symbol_reference)) {
-                                       is_non_null = true;
-                                       break;
-                               }
-                               b = b.parent;
-                       }
+                       this.get_nullability_state (access.inner.symbol_reference, out is_null, out 
is_non_null);
 
                        if (is_null) {
                                Report.error (access.source_reference, "`%s' is null here".printf 
(access.to_string ()));
-                       } else if (access.inner.symbol_reference != null) {
+                       } else {
                                DataType? symbol_type = context.analyzer.get_value_type_for_symbol 
(access.inner.symbol_reference, false);
                                if (symbol_type != null) {
                                        // If the referenced type is nullable, and the code didn't make sure 
the reference
@@ -87,30 +90,6 @@ public class Vala.NullabilityChecker : CodeVisitor {
                decl.accept_children (this);
        }
 
-       public override void visit_source_file (SourceFile source_file) {
-               source_file.accept_children (this);
-       }
-
-       public override void visit_class (Class cl) {
-               cl.accept_children (this);
-       }
-
-       public override void visit_struct (Struct st) {
-               st.accept_children (this);
-       }
-
-       public override void visit_interface (Interface iface) {
-               iface.accept_children (this);
-       }
-
-       public override void visit_enum (Enum en) {
-               en.accept_children (this);
-       }
-
-       public override void visit_error_domain (ErrorDomain ed) {
-               ed.accept_children (this);
-       }
-
        public override void visit_method (Method m) {
                m.accept_children (this);
        }
@@ -120,4 +99,27 @@ public class Vala.NullabilityChecker : CodeVisitor {
                        local.initializer.accept (this);
                }
        }
+
+       public override void visit_assignment (Assignment assign) {
+               if (assign.left != null && assign.right != null &&
+                   assign.left.symbol_reference != null && assign.right.symbol_reference != null) {
+                       DataType? left_type = context.analyzer.get_value_type_for_symbol 
(assign.left.symbol_reference, false);
+                       if (left_type != null && !left_type.nullable) {
+                               DataType? right_type = context.analyzer.get_value_type_for_symbol 
(assign.right.symbol_reference, false);
+                               if (right_type != null && right_type.nullable) {
+                                       bool is_null = false;
+                                       bool is_non_null = false;
+                                       this.get_nullability_state (assign.right.symbol_reference, out 
is_null, out is_non_null);
+                                       if (!is_non_null) {
+                                               Report.error (assign.source_reference, "Cannot assign from 
nullable `%s' to non-nullable `%s'".printf (right_type.to_string (), left_type.to_string ()));
+                                       }
+                               }
+                       }
+                       // Assignments from non-nullable to nullable are always fine
+               }
+       }
+
+       public override void visit_expression_statement (ExpressionStatement stmt) {
+               stmt.expression.accept (this);
+       }
 }