diff --git a/compiler/src/dmd/dcast.d b/compiler/src/dmd/dcast.d
index 172c8278f7..21ddd752ec 100644
--- a/compiler/src/dmd/dcast.d
+++ b/compiler/src/dmd/dcast.d
@@ -704,6 +704,12 @@ MATCH implicitConvTo(Expression e, Type t)
                 if (!tn.isConst() && !tn.isImmutable())
                     return MATCH.nomatch;
                 m = MATCH.constant;
+
+                // After converting e.g. ubyte[] to const(ubyte)[], don't change
+                // to MATCH.convert, return MATCH.constant
+                //  https://github.com/dlang/dmd/issues/20635
+                if (e.type.ty == t.ty && e.type.nextOf().ty == tn.ty)
+                    return m;
             }
             if (e.type != t && e.hexString && tn.isIntegral && (tn.size == e.sz || (!e.committed && (e.len % tn.size) == 0)))
             {
diff --git a/compiler/src/dmd/dsymbolsem.d b/compiler/src/dmd/dsymbolsem.d
index 63b9e693d0..73388081d1 100644
--- a/compiler/src/dmd/dsymbolsem.d
+++ b/compiler/src/dmd/dsymbolsem.d
@@ -4184,7 +4184,8 @@ private extern(C++) class AddMemberVisitor : Visitor
             }
 
             // If using C tag/prototype/forward declaration rules
-            if (sc.inCfile && !dsym.isImport())
+            if (sc && sc.inCfile && !dsym.isImport())
+            // When merging master, replace with: if (sc && sc.inCfile && !dsym.isImport())
             {
                 if (handleTagSymbols(*sc, dsym, s2, sds))
                     return;
diff --git a/compiler/src/dmd/expressionsem.d b/compiler/src/dmd/expressionsem.d
index 94c76591d4..6c0970e703 100644
--- a/compiler/src/dmd/expressionsem.d
+++ b/compiler/src/dmd/expressionsem.d
@@ -1453,11 +1453,6 @@ private Expression resolveUFCSProperties(Scope* sc, Expression e1, Expression e2
         auto arguments = new Expressions(1);
         (*arguments)[0] = eleft;
         e = new CallExp(loc, e, arguments);
-
-        // https://issues.dlang.org/show_bug.cgi?id=24017
-        if (sc.debug_)
-            e.isCallExp().inDebugStatement = true;
-
         e = e.expressionSemantic(sc);
         return e;
     }
@@ -13077,6 +13072,11 @@ private extern (C++) final class ExpressionSemanticVisitor : Visitor
             error(exp.loc, "compare not defined for complex operands");
             return setError();
         }
+        else if (t1.isTypeFunction() || t2.isTypeFunction())
+        {
+            error(exp.loc, "comparison is not defined for function types");
+            return setError();
+        }
         else if (t1.ty == Taarray || t2.ty == Taarray)
         {
             error(exp.loc, "`%s` is not defined for associative arrays", EXPtoString(exp.op).ptr);
@@ -13382,6 +13382,12 @@ private extern (C++) final class ExpressionSemanticVisitor : Visitor
             return;
         }
 
+        if (t1.isTypeFunction() || t2.isTypeFunction())
+        {
+            error(exp.loc, "operator `==` is not defined for function types");
+            return setError();
+        }
+
         if (auto tv = t1.isTypeVector())
             exp.type = tv.toBooleanVector();
 
@@ -13438,6 +13444,12 @@ private extern (C++) final class ExpressionSemanticVisitor : Visitor
         if (exp.e2.op == EXP.call)
             exp.e2 = (cast(CallExp)exp.e2).addDtorHook(sc);
 
+        if (exp.e1.type.isTypeFunction() || exp.e2.type.isTypeFunction())
+        {
+            error(exp.loc, "operator `is` is not defined for function types");
+            return setError();
+        }
+
         if (exp.e1.type.toBasetype().ty == Tsarray ||
             exp.e2.type.toBasetype().ty == Tsarray)
             deprecation(exp.loc, "identity comparison of static arrays "
diff --git a/compiler/src/dmd/pragmasem.d b/compiler/src/dmd/pragmasem.d
index c5d18ef40a..a7299a0e9b 100644
--- a/compiler/src/dmd/pragmasem.d
+++ b/compiler/src/dmd/pragmasem.d
@@ -567,7 +567,7 @@ private bool pragmaMsgSemantic(Loc loc, Scope* sc, Expressions* args)
         return false;
 
     buf.writestring("\n");
-    fprintf(stderr, buf.extractChars);
+    fprintf(stderr, "%s", buf.extractChars);
     return true;
 }
 
diff --git a/compiler/src/dmd/statementsem.d b/compiler/src/dmd/statementsem.d
index 4ad6e3c3ee..d19052b504 100644
--- a/compiler/src/dmd/statementsem.d
+++ b/compiler/src/dmd/statementsem.d
@@ -135,7 +135,16 @@ private Expression checkAssignmentAsCondition(Expression e, Scope* sc)
     return e;
 }
 
-// Performs semantic analysis in Statement AST nodes
+/**
+ * Performs semantic analysis in Statement AST nodes
+ *
+ * Params:
+ *   s = statement to perform semantic analysis on
+ *   sc = scope in which statement resides
+ *
+ * Returns: statement `s` after semantic analysis.
+ * Can be `null`, for example with `pragma(msg, "")`
+ */
 Statement statementSemantic(Statement s, Scope* sc)
 {
     import dmd.compiler;
@@ -3488,6 +3497,7 @@ Statement statementSemanticVisit(Statement s, Scope* sc)
             sc = sc.push();
             sc.debug_ = true;
             ds.statement = ds.statement.statementSemantic(sc);
+            debugThrowWalker(ds.statement);
             sc.pop();
         }
         result = ds.statement;
@@ -4760,7 +4770,6 @@ private Statements* flatten(Statement statement, Scope* sc)
                 if (dc)
                 {
                     s = new DebugStatement(cs.loc, cs.ifbody);
-                    debugThrowWalker(cs.ifbody);
                 }
                 else
                     s = cs.ifbody;
@@ -4932,7 +4941,8 @@ Params:
 */
 private void debugThrowWalker(Statement s)
 {
-
+    if (!s)
+        return;
     extern(C++) final class DebugWalker : SemanticTimeTransitiveVisitor
     {
         alias visit = SemanticTimeTransitiveVisitor.visit;
diff --git a/compiler/test/compilable/bug11735.d b/compiler/test/compilable/bug11735.d
index b94cb6e77d..be61a50585 100644
--- a/compiler/test/compilable/bug11735.d
+++ b/compiler/test/compilable/bug11735.d
@@ -13,6 +13,7 @@ print dstring
 foo_str
 foo_wstr
 foo_dstr
+X%nY
 ---
 */
 
@@ -33,4 +34,7 @@ void main()
     pragma(msg, a);
     pragma(msg, b);
     pragma(msg, c);
+
+    // https://github.com/dlang/dmd/issues/20894
+    pragma(msg, "X%nY");
 }
diff --git a/compiler/test/compilable/test16492.d b/compiler/test/compilable/debug_statement_attributes.d
similarity index 73%
rename from compiler/test/compilable/test16492.d
rename to compiler/test/compilable/debug_statement_attributes.d
index 833be1d8cf..bf762c001d 100644
--- a/compiler/test/compilable/test16492.d
+++ b/compiler/test/compilable/debug_statement_attributes.d
@@ -85,3 +85,17 @@ void test6() nothrow
         () {throw new Exception("");}();
     }
 }
+
+void writeln() {}
+void writeln(string) {}
+
+void test7() nothrow
+{
+    debug writeln("Hello"); // https://issues.dlang.org/show_bug.cgi?id=24017
+    debug "Hello".writeln;
+    debug writeln = "Hello"; // https://github.com/dlang/dmd/issues/20719
+    debug writeln;
+
+    // https://github.com/dlang/dmd/pull/20720#issuecomment-2596892489
+    debug pragma(msg, ""); // Came up as segfault, pragma statement became null after semantic
+}
diff --git a/compiler/test/compilable/test24017.d b/compiler/test/compilable/test24017.d
deleted file mode 100644
index 0d03978120..0000000000
--- a/compiler/test/compilable/test24017.d
+++ /dev/null
@@ -1,11 +0,0 @@
-// https://issues.dlang.org/show_bug.cgi?id=24017
-
-// REQUIRED_ARGS: -debug
-
-void writeln(string) {}
-
-void main() nothrow
-{
-    debug writeln("Hello");
-    debug "Hello".writeln;
-}
diff --git a/compiler/test/fail_compilation/fail22151.d b/compiler/test/fail_compilation/fail22151.d
index c6c3b1b742..9b5d5aad7b 100644
--- a/compiler/test/fail_compilation/fail22151.d
+++ b/compiler/test/fail_compilation/fail22151.d
@@ -2,10 +2,13 @@
 /*
 TEST_OUTPUT:
 ---
-fail_compilation/fail22151.d(14): Error: function `test` is not an lvalue and cannot be modified
-fail_compilation/fail22151.d(15): Error: function `test2` is not an lvalue and cannot be modified
-fail_compilation/fail22151.d(18): Error: function pointed to by `fp` is not an lvalue and cannot be modified
-fail_compilation/fail22151.d(21): Error: function pointed to by `ff` is not an lvalue and cannot be modified
+fail_compilation/fail22151.d(17): Error: function `test` is not an lvalue and cannot be modified
+fail_compilation/fail22151.d(18): Error: function `test2` is not an lvalue and cannot be modified
+fail_compilation/fail22151.d(21): Error: function pointed to by `fp` is not an lvalue and cannot be modified
+fail_compilation/fail22151.d(24): Error: function pointed to by `ff` is not an lvalue and cannot be modified
+fail_compilation/fail22151.d(27): Error: operator `==` is not defined for function types
+fail_compilation/fail22151.d(28): Error: operator `is` is not defined for function types
+fail_compilation/fail22151.d(29): Error: comparison is not defined for function types
 ---
 */
 
@@ -19,6 +22,11 @@ void test()
 
     auto ff = &test2;
     *ff = *&test2;
+
+    // https://github.com/dlang/dmd/issues/18281
+    const c = *fp == *fp;
+    const d = *fp is *fp;
+    const e = *fp < *fp;
 }
 
 void test2();
diff --git a/compiler/test/fail_compilation/test20859.d b/compiler/test/fail_compilation/test20859.d
new file mode 100644
index 0000000000..50fa9e0d49
--- /dev/null
+++ b/compiler/test/fail_compilation/test20859.d
@@ -0,0 +1,11 @@
+/**
+TEST_OUTPUT:
+---
+fail_compilation/test20859.d(8): Error: variable `test20859.ICE.__vtbl` conflicts with variable `test20859.ICE.__vtbl` at fail_compilation/test20859.d(10)
+---
+*/
+
+class ICE
+{
+    void **__vtbl;
+}
diff --git a/compiler/test/runnable/literal.d b/compiler/test/runnable/literal.d
index 3cc7e51197..c78f4776aa 100644
--- a/compiler/test/runnable/literal.d
+++ b/compiler/test/runnable/literal.d
@@ -277,8 +277,16 @@ void testHexstring()
     static immutable ulong[] z0 = cast(immutable ulong[]) x"1111 1111 1111 1111 0000 000F 0000 0000";
     static immutable ulong[] z1 = [0x1111_1111_1111_1111, 0x0000_000E_0000_0000];
     static assert(z0 !is z1);
+
+    // https://github.com/dlang/dmd/issues/20635
+    f20635(cast(ubyte[]) x"00");
+    f20635(cast(const ubyte[]) x"00");
+    f20635(cast(immutable ubyte[]) x"00");
 }
 
+void f20635(const ubyte[] value){}
+void f20635(const string value){}
+
 /***************************************************/
 
 int main()
diff --git a/compiler/test/runnable/template3.d b/compiler/test/runnable/template3.d
index e3313672d0..7b90cff29a 100644
--- a/compiler/test/runnable/template3.d
+++ b/compiler/test/runnable/template3.d
@@ -240,6 +240,16 @@ void test8()
 
 /*********************************************************/
 
+// https://github.com/dlang/dmd/issues/20907
+struct Bar { enum bar = 1; }
+void foo(A)(A[], A[1 << A.bar]) {}
+void test20907()
+{
+    foo((Bar[]).init, (Bar[2]).init);
+}
+
+/*********************************************************/
+
 int main()
 {
     test1();
@@ -250,6 +260,7 @@ int main()
     test6();
     test7();
     test8();
+    test20907();
 
     printf("Success\n");
     return 0;