Add "unused" warning

src/llex.h

@@ -210,6 +210,7 @@ enum WarningType : int {
   WT_UNANNOTATED_FALLTHROUGH,
   WT_DISCARDED_RETURN,
   WT_FIELD_SHADOW,
+  WT_UNUSED,
 
   NUM_WARNING_TYPES
 };
@@ -232,6 +233,7 @@ inline const char* const luaX_warnNames[] = {
   "unannotated-fallthrough",
   "discarded-return",
   "field-shadow",
+  "unused",
 };
 static_assert(sizeof(luaX_warnNames) / sizeof(const char*) == NUM_WARNING_TYPES);
 
@@ -263,6 +265,9 @@ class WarningConfig
 #endif
 #ifndef PLUTO_WARN_NON_PORTABLE_NAME
     case WT_NON_PORTABLE_NAME:
+#endif
+#ifndef PLUTO_WARN_UNSUED
+    case WT_UNUSED:  /* it kills me that I can't enable this by default but our test suite is horrible right now */
 #endif
     case NUM_WARNING_TYPES:  /* dummy case so compiler doesn't cry when all macros are set */
       return WS_OFF;

src/lparser.cpp

@@ -475,8 +475,7 @@ static int registerlocalvar (LexState *ls, FuncState *fs, TString *varname) {
 
 
 #define new_localvarliteral(ls,v) \
-    new_localvar(ls,  \
-      luaX_newstring(ls, "" v, (sizeof(v)/sizeof(char)) - 1));
+    new_localvar(ls, luaX_newstring(ls, "" v, (sizeof(v)/sizeof(char)) - 1), {}, true);
 
 
 [[nodiscard]] static TypeHint* new_typehint (LexState *ls) {
@@ -694,7 +693,7 @@ static void checkforshadowing (LexState *ls, FuncState *fs, const std::unordered
 ** Create a new local variable with the given 'name'. Return its index
 ** in the function.
 */
-static int new_localvar (LexState *ls, TString *name, int line, TypeHint hint = {}, bool check_globals = true) {
+static int new_localvar (LexState *ls, TString *name, int line, TypeHint hint = {}, bool check_globals = true, bool used = false) {
   lua_State *L = ls->L;
   FuncState *fs = ls->fs;
   Dyndata *dyd = ls->dyd;
@@ -710,11 +709,12 @@ static int new_localvar (LexState *ls, TString *name, int line, TypeHint hint =
     *var->vd.hint = std::move(hint);
   var->vd.name = name;
   var->vd.line = line;
+  var->vd.used = used;
   return dyd->actvar.n - 1 - fs->firstlocal;
 }
 
-static int new_localvar (LexState *ls, TString *name, TypeHint hint = {}) {
-  return new_localvar(ls, name, ls->getLineNumber(), std::move(hint));
+static int new_localvar (LexState *ls, TString *name, TypeHint hint = {}, bool used = false) {
+  return new_localvar(ls, name, ls->getLineNumber(), std::move(hint), true, used);
 }
 
 
@@ -725,7 +725,9 @@ static void init_var (FuncState *fs, expdesc *e, int vidx) {
   e->f = e->t = NO_JUMP;
   e->k = VLOCAL;
   e->u.var.vidx = vidx;
-  e->u.var.ridx = getlocalvardesc(fs, vidx)->vd.ridx;
+  Vardesc *vd = getlocalvardesc(fs, vidx);
+  e->u.var.ridx = vd->vd.ridx;
+  vd->vd.used = true;
 }
 
 
@@ -789,6 +791,15 @@ static void removevars (FuncState *fs, int tolevel) {
     LocVar *var = localdebuginfo(fs, --fs->nactvar);
     if (var)  /* does it have debug information? */
       var->endpc = fs->pc;
+    Vardesc *vd = getlocalvardesc(fs, fs->nactvar);
+    if (!vd->vd.used
+      && (vd->vd.kind == VDKREG || vd->vd.kind == RDKTOCLOSE)  /* only care if variable is in a register + we don't detect constants being used */
+      && getstr(vd->vd.name)[0] != '_'  /* common prefix for intentionally unused variables, assume it's intentional */
+      && !eqstr(vd->vd.name, luaX_newliteral(fs->ls, "self"))  /* not an issue if the var is generated by Pluto, but still possible with manual method definition */
+      ) {
+      throw_warn(fs->ls, "unused local variable", luaO_fmt(fs->ls->L, "'%s' is unused", getstr(vd->vd.name)), vd->vd.line, WT_UNUSED);
+      fs->ls->L->top.p--;  /* pop result of luaO_fmt */
+    }
   }
 }
 
@@ -825,8 +836,10 @@ static int newupvalue (FuncState *fs, TString *name, expdesc *v) {
   if (v->k == VLOCAL) {
     up->instack = 1;
     up->idx = v->u.var.ridx;
-    up->kind = getlocalvardesc(prev, v->u.var.vidx)->vd.kind;
-    lua_assert(eqstr(name, getlocalvardesc(prev, v->u.var.vidx)->vd.name));
+    Vardesc *vd = getlocalvardesc(prev, v->u.var.vidx);
+    up->kind = vd->vd.kind;
+    lua_assert(eqstr(name, vd->vd.name));
+    vd->vd.used = true;
   }
   else {
     lua_assert(v->k == VUPVAL);
@@ -4305,9 +4318,9 @@ static void forvlist (LexState *ls, TypeHint *prop) {
   new_localvarliteral(ls, "(for state)");
   new_localvarliteral(ls, "(for state)");
   /* create variable for key */
-  new_localvar(ls, luaS_newliteral(ls->L, "(for state)"));
+  new_localvar(ls, luaS_newliteral(ls->L, "(for state)"), {}, true);
   /* create variable for value */
-  int vidx = new_localvar(ls, luaS_newliteral(ls->L, "(for state)"));
+  int vidx = new_localvar(ls, luaS_newliteral(ls->L, "(for state)"), {}, true);
   nvars++;
 
   line = ls->getLineNumber();

src/lparser.h

@@ -345,6 +345,7 @@ typedef union Vardesc {
     short pidx;  /* index of the variable in the Proto's 'locvars' array */
     TString *name;  /* variable name */
     int line;
+    bool used;
   } vd;
   TValue k;  /* constant value (if any) */
 } Vardesc;

src/luaconf.h

@@ -848,6 +848,9 @@
 // If defined, the "non-portable-name" warning is enabled by default.
 //#define PLUTO_WARN_NON_PORTABLE_NAME
 
+// If defined, the "unused" warning is enabled by default.
+//#define PLUTO_WARN_UNUSED
+
 /*
 ** {====================================================================
 ** Pluto Configuration: Compatibility