Compiler: fix a couple of issues with while and rescue

spec/compiler/codegen/while_spec.cr

@@ -165,4 +165,19 @@ describe "Codegen: while" do
       10
       )).to_i.should eq(10)
   end
+
+  it "doesn't crash on while true begin break rescue (#7786)" do
+    codegen(%(
+      require "prelude"
+
+      while true
+        begin
+          foo = 1
+          break
+        rescue
+        end
+      end
+      foo
+      ))
+  end
 end

spec/compiler/semantic/while_spec.cr

@@ -197,4 +197,33 @@ describe "Semantic: while" do
       b
       )) { nilable types["Foo"] }
   end
+
+  it "doesn't type var as nilable after break inside rescue" do
+    assert_type(%(
+      while true
+        begin
+          foo = 1
+          break
+        rescue
+        end
+      end
+      foo
+      )) { int32 }
+  end
+
+  it "types variable as nilable if raise before assign" do
+    assert_type(%(
+      require "prelude"
+
+      while true
+        begin
+          raise "oops"
+          foo = 12345
+        rescue
+        end
+        break
+      end
+      foo
+      )) { nilable int32 }
+  end
 end

src/compiler/crystal/semantic/main_visitor.cr

@@ -352,6 +352,10 @@ module Crystal
         check_closured meta_var
 
         if var.nil_if_read?
+          # Once we know a variable is nil if read we mark it as nilable
+          var.bind_to(@program.nil_var)
+          var.nil_if_read = false
+
           meta_var.bind_to(@program.nil_var) unless meta_var.dependencies.try &.any? &.same?(@program.nil_var)
           node.bind_to(@program.nil_var)
         end
@@ -2193,18 +2197,21 @@ module Crystal
           after_while_var.bind_to(while_var)
           nilable = false
           if endless
-            # In an endless loop if there's a break before a variable is declared,
-            # that variable becomes nilable.
-            unless all_break_vars.try &.all? &.has_key?(name)
+            # In an endless loop if not all variable with the given name end up
+            # in a break it means that they can be nilable.
+            # Alternatively, if any var that ends in a break is nil-if-read then
+            # the resulting variable will be nil-if-read too.
+            if !all_break_vars.try(&.all? &.has_key?(name)) ||
+               all_break_vars.try(&.any? &.[name]?.try &.nil_if_read?)
               nilable = true
             end
           else
             nilable = true
           end
           if nilable
-            after_while_var.bind_to(@program.nil_var)
             after_while_var.nil_if_read = true
           end
+
           after_while_vars[name] = after_while_var
         end
       end
@@ -2827,7 +2834,6 @@ module Crystal
         rescue_vars.each do |name, var|
           after_var = (after_vars[name] ||= new_meta_var(name))
           if var.nil_if_read? || !body_vars[name]?
-            after_var.bind_to(program.nil_var)
             after_var.nil_if_read = true
           end
           after_var.bind_to(var)