Exclude variables' final types inside while true if re-assigned before first break

spec/compiler/semantic/while_spec.cr

@@ -170,6 +170,80 @@ describe "Semantic: while" do
       )) { nilable int32 }
   end
 
+  it "doesn't use type at end of endless while if variable is reassigned" do
+    assert_type(%(
+      while true
+        a = 1
+        if 1 == 1
+          break
+        end
+        a = 'x'
+      end
+      a
+      )) { int32 }
+  end
+
+  it "doesn't use type at end of endless while if variable is reassigned (2)" do
+    assert_type(%(
+      a = ""
+      while true
+        a = 1
+        if 1 == 1
+          break
+        end
+        a = 'x'
+      end
+      a
+      )) { int32 }
+  end
+
+  it "doesn't use type at end of endless while if variable is reassigned (3)" do
+    assert_type(%(
+      a = {1}
+      while true
+        a = a[0]
+        if 1 == 1
+          break
+        end
+        a = {'x'}
+      end
+      a
+      )) { union_of(int32, char) }
+  end
+
+  it "uses type at end of endless while if variable is reassigned, but not before first break" do
+    assert_type(%(
+      while true
+        if 1 == 1
+          break
+        end
+        a = 1
+        if 1 == 1
+          break
+        end
+        a = 'x'
+      end
+      a
+      )) { nilable union_of(int32, char) }
+  end
+
+  it "uses type at end of endless while if variable is reassigned, but not before first break (2)" do
+    assert_type(%(
+      a = ""
+      while true
+        if 1 == 1
+          break
+        end
+        a = 1
+        if 1 == 1
+          break
+        end
+        a = 'x'
+      end
+      a
+      )) { union_of(int32, char, string) }
+  end
+
   it "rebinds condition variable after while body (#6158)" do
     assert_type(%(
       class Foo

src/compiler/crystal/semantic/main_visitor.cr

@@ -2139,8 +2139,14 @@ module Crystal
 
           # If the loop is endless
           if endless
-            after_while_var.bind_to(while_var)
-            after_while_var.nil_if_read = while_var.nil_if_read?
+            # If a variable was re-assigned before the first break expression,
+            # the type at the end of the while body is inaccessible upon exit
+            # because the assignment must have executed before the next chance
+            # to break
+            unless all_break_vars.try(&.first?.try &.[name]?.try { |var| !while_var.same?(var) })
+              after_while_var.bind_to(while_var)
+              after_while_var.nil_if_read = while_var.nil_if_read?
+            end
           else
             # We need to bind to the variable *before* the condition, even
             # after before the variables that are used in the condition
@@ -2159,7 +2165,10 @@ module Crystal
           # outside it must be nilable, unless the loop is endless.
         else
           after_while_var = MetaVar.new(name)
-          after_while_var.bind_to(while_var)
+          unless endless && all_break_vars.try(&.first?.try &.[name]?.try { |var| !while_var.same?(var) })
+            after_while_var.bind_to(while_var)
+          end
+
           nilable = false
           if endless
             # In an endless loop if not all variable with the given name end up