Update diff pair rule syntax to be clearer.

Fixes https://gitlab.com/kicad/code/kicad/issues/8010

pcbnew/dialogs/panel_setup_rules_help.md

@@ -110,10 +110,6 @@ True if any part of `A` lies within the given zone's outline.
 
     A.isPlated()
 True if `A` has a hole which is plated.
-<br><br>
-
-    A.isDiffPair()
-True if `A` has a net that is part of a differential pair.
 <br><br>
 
     A.inDiffPair('<net_name>')
@@ -122,7 +118,7 @@ True if `A` has net that is part of the specified differential pair.
 matches items in the `CLK_P` and `CLK_N` nets.
 <br><br>
 
-    A.isCoupledDiffPair()
+    AB.isCoupledDiffPair()
 True if `A` and `B` are members of the same diff pair.
 <br><br>
 
@@ -191,12 +187,12 @@ For the latter use a `(layer "layer_name")` clause in the rule.
         (condition "A.Pad_Type == 'Through-hole'"))
 
 
-    # Specify a larger clearance around a particular diff-pair
-    (rule "dp clearance"
-        (constraint clearance (min "1.5mm"))
-        (condition "A.inDiffPair('CLK')"))
+    # Specify an optimal gap for a particular diff-pair
+    (rule "dp clock gap"
+        (constraint diff_pair_gap (opt "0.8mm"))
+        (condition "A.inDiffPair('CLK') && AB.isCoupledDiffPair()"))
 
     # Specify a larger clearance around any diff-pair
     (rule "dp clearance"
         (constraint clearance (min "1.5mm"))
-        (condition "A.isDiffPair() && !A.isCoupledDiffPair()"))
+        (condition "A.inDiffPair('*') && !AB.isCoupledDiffPair()"))

pcbnew/drc/drc_engine.cpp

@@ -266,7 +266,7 @@ void DRC_ENGINE::loadImplicitRules()
                                                              ncName );
                     netclassRule->m_Implicit = true;
 
-                    expr = wxString::Format( "A.NetClass == '%s' && A.isDiffPair()",
+                    expr = wxString::Format( "A.NetClass == '%s' && A.inDiffPair('*')",
                                              ncName );
                     netclassRule->m_Condition = new DRC_RULE_CONDITION( expr );
                     netclassItemSpecificRules.push_back( netclassRule );
@@ -295,7 +295,7 @@ void DRC_ENGINE::loadImplicitRules()
                                                              ncName );
                     netclassRule->m_Implicit = true;
 
-                    expr = wxString::Format( "A.NetClass == '%s' && A.isCoupledDiffPair()",
+                    expr = wxString::Format( "A.NetClass == '%s' && AB.isCoupledDiffPair()",
                                              ncName );
                     netclassRule->m_Condition = new DRC_RULE_CONDITION( expr );
                     netclassItemSpecificRules.push_back( netclassRule );

pcbnew/pcb_expr_evaluator.cpp

@@ -708,26 +708,6 @@ static void isBlindBuriedVia( LIBEVAL::CONTEXT* aCtx, void* self )
 }
 
 
-static void isDiffPair( LIBEVAL::CONTEXT* aCtx, void* self )
-{
-    PCB_EXPR_VAR_REF* vref = static_cast<PCB_EXPR_VAR_REF*>( self );
-    BOARD_ITEM*       item = vref ? vref->GetObject( aCtx ) : nullptr;
-    LIBEVAL::VALUE*   result = aCtx->AllocValue();
-
-    result->Set( 0.0 );
-    aCtx->Push( result );
-
-    if( item && item->IsConnected() )
-    {
-        NETINFO_ITEM* netinfo = static_cast<BOARD_CONNECTED_ITEM*>( item )->GetNet();
-        int dummy_p, dummy_n;
-
-        if( netinfo && DRC_ENGINE::IsNetADiffPair( item->GetBoard(), netinfo, dummy_p, dummy_n ) )
-            result->Set( 1.0 );
-    }
-}
-
-
 static void isCoupledDiffPair( LIBEVAL::CONTEXT* aCtx, void* self )
 {
     PCB_EXPR_CONTEXT*     context = static_cast<PCB_EXPR_CONTEXT*>( aCtx );
@@ -806,7 +786,6 @@ void PCB_EXPR_BUILTIN_FUNCTIONS::RegisterAllFunctions()
     RegisterFunc( "isBlindBuriedVia()", isBlindBuriedVia );
     RegisterFunc( "memberOf('x')", memberOf );
     RegisterFunc( "fromTo('x','y')", exprFromTo );
-    RegisterFunc( "isDiffPair()", isDiffPair );
     RegisterFunc( "isCoupledDiffPair()", isCoupledDiffPair );
     RegisterFunc( "inDiffPair('x')", inDiffPair );
 }
@@ -964,7 +943,7 @@ std::unique_ptr<LIBEVAL::VAR_REF> PCB_EXPR_UCODE::CreateVarRef( const wxString&
             return nullptr;
     }
 
-    if( aVar == "A" )
+    if( aVar == "A" || aVar == "AB" )
         vref = std::make_unique<PCB_EXPR_VAR_REF>( 0 );
     else if( aVar == "B" )
         vref = std::make_unique<PCB_EXPR_VAR_REF>( 1 );