Fix ZERODLY to not warn on 'wait(0)'.

Changes

@@ -35,6 +35,7 @@ Verilator 5.015 devel
 * Fix reference to extended class in parameterized class (#4466).
 * Fix display %x formatting of real.
 * Fix mis-warning on #() in classes' own functions.
+* Fix ZERODLY to not warn on 'wait(0)'.
 
 
 Verilator 5.014 2023-08-06

docs/guide/warnings.rst

@@ -1990,11 +1990,15 @@ List Of Warnings
 
    .. code-block:: sv
 
-         wait(0);  // Blocks forever
+         wait(1);  // Blocks forever
 
    Warns that a `wait` statement awaits a constant condition, which means it
    either blocks forever or never blocks.
 
+   As a special case `wait(0)` with the literal constant `0` (as opposed to
+   something that elaborates to zero), does not warn, as it is presumed the
+   code is making the intent clear.
+
 
 .. option:: WIDTH
 

src/V3LinkParse.cpp

@@ -591,6 +591,17 @@ private:
             iterateChildren(nodep);
         }
     }
+    void visit(AstWait* nodep) override {
+        cleanFileline(nodep);
+        iterateChildren(nodep);
+        if (nodep->condp()->isZero()) {
+            // Special case "wait(0)" we won't throw WAITCONST as user wrote
+            // it that way with presumed intent - UVM does this.
+            FileLine* const newfl = nodep->fileline();
+            newfl->warnOff(V3ErrorCode::WAITCONST, true);
+            nodep->fileline(newfl);
+        }
+    }
     void visit(AstWhile* nodep) override {
         cleanFileline(nodep);
         VL_RESTORER(m_insideLoop);

src/V3Timing.cpp

@@ -997,7 +997,9 @@ private:
         AstNodeExpr* const condp = V3Const::constifyEdit(nodep->condp()->unlinkFrBack());
         auto* const constp = VN_CAST(condp, Const);
         if (constp) {
-            condp->v3warn(WAITCONST, "Wait statement condition is constant");
+            if (!nodep->fileline()->warnIsOff(V3ErrorCode::WAITCONST)) {
+                condp->v3warn(WAITCONST, "Wait statement condition is constant");
+            }
             if (constp->isZero()) {
                 // We have to await forever instead of simply returning in case we're deep in a
                 // callstack

test_regress/t/t_lint_wait_bad.out

@@ -6,9 +6,6 @@
 %Warning-WAITCONST: t/t_timing_wait1.v:54:14: Wait statement condition is constant
    54 |       wait(0 < 1) $write("*-* All Finished *-*\n");
       |              ^
-%Warning-WAITCONST: t/t_timing_wait1.v:58:17: Wait statement condition is constant
-   58 |    initial wait(0) $stop;
-      |                 ^
 %Warning-WAITCONST: t/t_timing_wait1.v:59:19: Wait statement condition is constant
    59 |    initial wait(1 == 0) $stop;
       |                   ^~

test_regress/t/t_timing_wait1.v

@@ -55,7 +55,7 @@ module t;
       $finish;
    end
 
-   initial wait(0) $stop;
+   initial wait(0) $stop;  // Note this doesn't give WAITCONST
    initial wait(1 == 0) $stop;
 
    initial #12 $stop; // timeout