Analyser: detect and report unused recursive functions

Author: chqrlie

analyser/module_analyser_call.c2

@@ -56,7 +56,7 @@ fn QualType Analyser.analyseCallExpr(Analyser* ma, Expr** e_ptr) {
     */
 
     FunctionDecl* fd = ft.getDecl();
-    fd.asDecl().setUsed();
+    if (fd != ma.curFunction) fd.asDecl().setUsed();
     if (fd.hasAttrNoReturn()) call.setNoreturn();
 
     if (fd.isTemplate()) {
@@ -702,7 +702,7 @@ fn QualType Analyser.analysePureCallExpr(Analyser* ma, Expr* e) {
     }
 
     FunctionDecl* fd = ft.getDecl();
-    fd.asDecl().setUsed();
+    if (fd != ma.curFunction) fd.asDecl().setUsed();
 
     if (!fd.hasAttrPure()) {
         ma.error(e.getLoc(), "only pure functions can be called in global initializers");

analyser/module_analyser_expr.c2

@@ -154,8 +154,9 @@ fn Decl* Analyser.analyseIdentifier(Analyser* ma, Expr** e_ptr, u32 side) {
     e.setType(qt);
     i.setDecl(d);
 
-    if (side & RHS || side == 0) d.setUsed();
-    else {
+    if (side & RHS || side == 0) {
+        if (d != (Decl*)ma.curFunction) d.setUsed();
+    } else {
         // parameters are used if LHS|RHS
         if (d.isVarDecl()) {
             VarDecl* vd = (VarDecl*)d;

test/functions/unused_recursive.c2

@@ -0,0 +1,9 @@
+module test;
+
+fn i32 fib(i32 n) {     // @warning{unused function 'test.fib'}
+    return n <= 2 ? 1 : fib(n - 1) + fib(n - 2);
+}
+
+public fn i32 main() {
+    return 1;
+}