From ca4f0b8344e22e827799457c45ce40a6242657f5 Mon Sep 17 00:00:00 2001
From: wixoa <wixoag@gmail.com>
Date: Mon, 12 Feb 2024 10:51:24 -0800
Subject: [PATCH] Add "null statements" to the compiler (#1670)

---
 .../DMProject/Tests/Statements/EmptyBlock.dm         |  5 +++++
 .../Tests/Statements/EmptyBlockSuppressed.dm         |  5 +++++
 DMCompiler/Compiler/DM/DMAST.cs                      | 12 ++++++++++++
 DMCompiler/Compiler/DM/DMParser.cs                   |  7 +++++++
 DMCompiler/DM/Visitors/DMASTSimplifier.cs            |  2 ++
 DMCompiler/DM/Visitors/DMProcBuilder.cs              |  1 +
 6 files changed, 32 insertions(+)
 create mode 100644 Content.Tests/DMProject/Tests/Statements/EmptyBlock.dm
 create mode 100644 Content.Tests/DMProject/Tests/Statements/EmptyBlockSuppressed.dm

diff --git a/Content.Tests/DMProject/Tests/Statements/EmptyBlock.dm b/Content.Tests/DMProject/Tests/Statements/EmptyBlock.dm
new file mode 100644
index 0000000000..44ef88f06c
--- /dev/null
+++ b/Content.Tests/DMProject/Tests/Statements/EmptyBlock.dm
@@ -0,0 +1,5 @@
+// COMPILE ERROR
+#pragma EmptyBlock error
+
+/proc/RunTest()
+	if (TRUE)
\ No newline at end of file
diff --git a/Content.Tests/DMProject/Tests/Statements/EmptyBlockSuppressed.dm b/Content.Tests/DMProject/Tests/Statements/EmptyBlockSuppressed.dm
new file mode 100644
index 0000000000..2d52b13608
--- /dev/null
+++ b/Content.Tests/DMProject/Tests/Statements/EmptyBlockSuppressed.dm
@@ -0,0 +1,5 @@
+#pragma EmptyBlock error
+
+/proc/RunTest()
+	if (TRUE)
+		;
\ No newline at end of file
diff --git a/DMCompiler/Compiler/DM/DMAST.cs b/DMCompiler/Compiler/DM/DMAST.cs
index e80b68851e..fc3ce3467e 100644
--- a/DMCompiler/Compiler/DM/DMAST.cs
+++ b/DMCompiler/Compiler/DM/DMAST.cs
@@ -37,6 +37,10 @@ public void VisitObjectVarOverride(DMASTObjectVarOverride objectVarOverride) {
             throw new NotImplementedException();
         }
 
+        public void VisitNullProcStatement(DMASTNullProcStatement nullProcStatement) {
+            throw new NotImplementedException();
+        }
+
         public void VisitProcStatementExpression(DMASTProcStatementExpression statementExpression) {
             throw new NotImplementedException();
         }
@@ -772,6 +776,14 @@ public override void Visit(DMASTVisitor visitor) {
         }
     }
 
+    /// Lone semicolon, analogous to null statements in C.
+    /// Main purpose is to suppress EmptyBlock emissions.
+    public sealed class DMASTNullProcStatement(Location location) : DMASTProcStatement(location) {
+        public override void Visit(DMASTVisitor visitor) {
+            visitor.VisitNullProcStatement(this);
+        }
+    }
+
     public sealed class DMASTProcStatementExpression : DMASTProcStatement {
         public DMASTExpression Expression;
 
diff --git a/DMCompiler/Compiler/DM/DMParser.cs b/DMCompiler/Compiler/DM/DMParser.cs
index d0de271eae..51da75118a 100644
--- a/DMCompiler/Compiler/DM/DMParser.cs
+++ b/DMCompiler/Compiler/DM/DMParser.cs
@@ -194,6 +194,7 @@ public DMASTFile File() {
 
         public DMASTStatement? Statement(bool requireDelimiter = true) {
             var loc = Current().Location;
+
             DMASTPath? path = Path();
             if (path is null)
                 return null;
@@ -618,6 +619,12 @@ public DMASTFile File() {
 
         public DMASTProcStatement? ProcStatement() {
             var loc = Current().Location;
+
+            if (Current().Type == TokenType.DM_Semicolon) { // A lone semicolon creates a "null statement" (like C)
+                // Note that we do not consume the semicolon here
+                return new DMASTNullProcStatement(loc);
+            }
+
             var leadingColon = Check(TokenType.DM_Colon);
 
             DMASTExpression? expression = null;
diff --git a/DMCompiler/DM/Visitors/DMASTSimplifier.cs b/DMCompiler/DM/Visitors/DMASTSimplifier.cs
index 1956f95884..5e9f1529e7 100644
--- a/DMCompiler/DM/Visitors/DMASTSimplifier.cs
+++ b/DMCompiler/DM/Visitors/DMASTSimplifier.cs
@@ -53,6 +53,8 @@ public void VisitProcBlockInner(DMASTProcBlockInner procBlockInner) {
             }
         }
 
+        public void VisitNullProcStatement(DMASTNullProcStatement nullProcStatement) { }
+
         public void VisitProcStatementExpression(DMASTProcStatementExpression statementExpression) {
             SimplifyExpression(ref statementExpression.Expression);
         }
diff --git a/DMCompiler/DM/Visitors/DMProcBuilder.cs b/DMCompiler/DM/Visitors/DMProcBuilder.cs
index 59fa4828d1..7b946ffe3a 100644
--- a/DMCompiler/DM/Visitors/DMProcBuilder.cs
+++ b/DMCompiler/DM/Visitors/DMProcBuilder.cs
@@ -112,6 +112,7 @@ private void ProcessBlockInner(DMASTProcBlockInner block, bool silenceEmptyBlock
 
         public void ProcessStatement(DMASTProcStatement statement) {
             switch (statement) {
+                case DMASTNullProcStatement: break;
                 case DMASTProcStatementExpression statementExpression: ProcessStatementExpression(statementExpression); break;
                 case DMASTProcStatementContinue statementContinue: ProcessStatementContinue(statementContinue); break;
                 case DMASTProcStatementGoto statementGoto: ProcessStatementGoto(statementGoto); break;