!54 feat: 禁止全局变量重复声明

Merge pull request !54 from Luke/bugfix/fix-global-redeclare-error

.run/Bug6.run.xml

@@ -0,0 +1,10 @@
+<component name="ProjectRunConfigurationManager">
+  <configuration default="false" name="Bug6" type="Application" factoryName="Application" folderName="BugFarm">
+    <option name="MAIN_CLASS_NAME" value="org.jcnc.snow.cli.SnowCLI" />
+    <module name="Snow" />
+    <option name="PROGRAM_PARAMETERS" value="compile run -d playground/BugFarm/Bug6 -o target/Bug6 --debug" />
+    <method v="2">
+      <option name="Make" enabled="true" />
+    </method>
+  </configuration>
+</component>

playground/BugFarm/Bug6/Main.snow

@@ -0,0 +1,13 @@
+module: Main
+    import: os
+    globals:
+        declare sum: int = 123
+    function: main
+        parameter:
+        return_type: int
+        body:
+            os.print(sum)
+            return 0
+        end body
+    end function
+end module

playground/BugFarm/Bug6/OS.snow

@@ -0,0 +1,11 @@
+module: os
+    import: os
+    function: print
+        parameter:
+            declare i1: int
+        return_type: void
+        body:
+            syscall("PRINT",i1)
+        end body
+    end function
+end module

src/main/java/org/jcnc/snow/compiler/semantic/core/FunctionChecker.java

@@ -59,7 +59,13 @@ public record FunctionChecker(Context ctx) {
             SymbolTable globalScope = new SymbolTable(null);
             for (DeclarationNode g : mod.globals()) {
                 var t = ctx.parseType(g.getType());
-                globalScope.define(new Symbol(g.getName(), t, SymbolKind.VARIABLE));
+                // 检查全局变量是否重复声明
+                if (!globalScope.define(new Symbol(g.getName(), t, SymbolKind.VARIABLE))) {
+                    ctx.errors().add(new SemanticError(
+                            g,
+                            "全局变量重复声明: " + g.getName()
+                    ));
+                }
             }
 
             // 遍历模块中所有函数定义