Fix broken `verilator_config removal

"dummy variable trick" introduced in [1]:
- Results in syntax error that is not rolled back, causing sv-bugpoint
to not minimize anything at all if `verilator_config is present
- Relies on not-always-true assumtion that `verilator_config block is
recognized by slang as trivia

This commit:
- goes back to removing `verilator_config as separate step
- recognizes `begin_keywords as a way to go back from config mode to
  systemverilog mode

[1]: 533abc2 ("Add support for multi-file designs", 2025-02-26)
9e15f30

Author: sgizler

source/SvBugpoint.cpp

@@ -120,19 +120,7 @@ bool SvBugpoint::pass(std::shared_ptr<SyntaxTree>& tree, const std::string& pass
 }
 
 void SvBugpoint::minimize() {
-    for (size_t i = 0; i < paths.size(); i++) {
-        currentPathIdx = i;
-        // Append a dummy variable to the end of the file
-        // Slang appends unknown directives to the next valid Syntax node, but
-        // if no such node exists, they are not appended to anything.
-        // This dummy variable allows to remove this directive as part of the DeclRemover pass.
-        // Example of such directive is `verilator_config
-        std::ofstream testFile(getOutput(), std::ios::app);
-        testFile << "int __SV_BUGPOINT_" << currentPathIdx << "_;" << std::endl;
-        testFile << std::flush;
-        testFile.close();
-    }
-
+    removeVerilatorConfig();
     bool anyChange = true;
     while (anyChange) {
         anyChange = false;
@@ -184,6 +172,35 @@ void SvBugpoint::minimize() {
     }
 }
 
+void SvBugpoint::removeVerilatorConfig() {
+    auto info = AttemptStats("-", "verilatorConfigRemover", this);
+    for (size_t i = 0; i < paths.size(); i++) {
+        currentPathIdx = i;
+        std::ifstream inputFile(getOutput());
+        std::ofstream testFile(getTmpOutput());
+        std::string line;
+        bool doSkip = false;
+        bool skippedSomething = false;
+        while (std::getline(inputFile, line)) {
+            if (line == "`verilator_config") {
+                doSkip = true;
+                skippedSomething = true;
+            } else if (doSkip && line.starts_with("`begin_keywords")) {
+                doSkip = false;
+                // There is chance that `begin_keywords is meant to do more than
+                // merely exit configuration block, so we don't skip it.
+                testFile << line << "\n";
+            } else if (!doSkip) {
+                testFile << line << "\n";
+            }
+        }
+        testFile << std::flush;
+        if (skippedSomething) {  // no reason to test if no modification was done
+            test(info);
+        }
+    }
+}
+
 void SvBugpoint::initOutDir() {
     mkdir(getOutDir());
     if (!std::filesystem::is_empty(getOutDir()) && !force.value_or(false)) {

source/SvBugpoint.hpp

@@ -27,6 +27,7 @@ class SvBugpoint {
     void setCurrentAttemptIdx(int idx) { currentAttemptIdx = idx; }
     void dryRun();
     void initOutDir();
+    void removeVerilatorConfig();
     void minimize();
     bool pass(std::shared_ptr<SyntaxTree>& tree, const std::string& passIdx = "-");
 

tests/golden/short_exit0/sv-bugpoint-minimized.sv

@@ -0,0 +1,2 @@
+
+

tests/golden/short_exit1/sv-bugpoint-minimized.sv

@@ -36,6 +36,9 @@ typedef struct {
         int b;
 } struct_foo;
 
+`verilator_config
+lint_off -rule UNUSED -file "*/rtl/prim_onehot_check.sv" -match "Signal is not used: 'clk_i'"
+`begin_keywords "1800-2012"
 module serial_adder #(WIDTH=32) (
         input  [WIDTH-1:0] a,
         input  [WIDTH-1:0] b,
@@ -64,3 +67,5 @@ module serial_adder #(WIDTH=32) (
 
 endmodule
 
+`verilator_config
+lint_off -rule UNUSED -file "*/rtl/prim_onehot_check.sv" -match "Signal is not used: 'clk_i'"

tests/golden/short_grep/sv-bugpoint-minimized.sv

@@ -3,3 +3,4 @@
 module full_adder3 (
         input cin);
 endmodule
+

tests/golden/short_multifile_flag_f_verilator_errmsg/sv-bugpoint-minimized.sv

@@ -9,6 +9,8 @@
 
 
 
+
+
 typedef struct {
         int b;
 } struct_foo;
@@ -22,3 +24,4 @@ module serial_adder #() ();
     assign foo.c = 0;
 
 endmodule
+

tests/golden/short_multifile_flag_y_verilator_errmsg/sv-bugpoint-minimized.sv

@@ -9,6 +9,8 @@
 
 
 
+
+
 typedef struct {
         int b;
 } struct_foo;
@@ -22,3 +24,4 @@ module serial_adder #() ();
     assign foo.c = 0;
 
 endmodule
+

tests/golden/short_multifile_verilator_errmsg/sv-bugpoint-minimized.sv

@@ -9,6 +9,8 @@
 
 
 
+
+
 typedef struct {
         int b;
 } struct_foo;
@@ -22,3 +24,4 @@ module serial_adder #() ();
     assign foo.c = 0;
 
 endmodule
+

tests/golden/short_verilator_errmsg/sv-bugpoint-minimized.sv

@@ -4,6 +4,7 @@ typedef struct {
         int b;
 } struct_foo;
 
+`begin_keywords "1800-2012"
 module serial_adder #() ();
 
     generate
@@ -13,3 +14,4 @@ module serial_adder #() ();
     assign foo.c = 0;
 
 endmodule
+

tests/input_files/short_in.sv

@@ -36,6 +36,9 @@ typedef struct {
         int b;
 } struct_foo;
 
+`verilator_config
+lint_off -rule UNUSED -file "*/rtl/prim_onehot_check.sv" -match "Signal is not used: 'clk_i'"
+`begin_keywords "1800-2012"
 module serial_adder #(WIDTH=32) (
         input  [WIDTH-1:0] a,
         input  [WIDTH-1:0] b,
@@ -64,3 +67,5 @@ module serial_adder #(WIDTH=32) (
 
 endmodule
 
+`verilator_config
+lint_off -rule UNUSED -file "*/rtl/prim_onehot_check.sv" -match "Signal is not used: 'clk_i'"