[slang] Fix static subroutine local variables multiple assigns and reduce MultipleAlwaysAssigns diag severity

scripts/diagnostics.txt

@@ -665,7 +665,6 @@ error InOutVarPortConn "'{}' cannot be connected to 'inout' port (only nets are
 error InOutUWireConn "'uwire' net '{}' cannot be connected to 'inout' port"
 error MixedVarAssigns "cannot mix continuous and procedural assignments to variable '{}'"
 error MultipleContAssigns "cannot have multiple continuous assignments to variable '{}'"
-error MultipleAlwaysAssigns "variable '{}' driven by {} procedure cannot be written to by any other process"
 error MultipleUWireDrivers "'uwire' net '{}' cannot have multiple drivers"
 error MultipleUDNTDrivers "net '{}' with user-defined nettype '{}' cannot have multiple drivers because it does not specify a resolution function"
 error InputPortAssign "cannot assign to input port '{}'"
@@ -705,6 +704,7 @@ warning sign-conversion SignConversion "implicit conversion changes signedness f
 warning float-bool-conv FloatBoolConv "implicit conversion from floating point type {} to boolean value"
 warning int-bool-conv IntBoolConv "implicit conversion from {} to boolean value"
 warning useless-cast UselessCast "useless cast from {} to the same type"
+warning multiple-always-assigns MultipleAlwaysAssigns "variable '{}' driven by {} procedure cannot be written to by any other process"
 
 subsystem Statements
 error ReturnNotInSubroutine "return statement is only valid inside task and function blocks"
@@ -1060,7 +1060,7 @@ group default = { real-underflow real-overflow vector-overflow int-overflow unco
                   raw-protect-eof protected-envelope specify-param dup-timing-path invalid-pulsestyle
                   negative-timing-limit bad-procedural-force duplicate-defparam implicit-port-type-mismatch
                   split-distweight-op dpi-pure-task multibit-edge unknown-sys-name unknown-library
-                  dup-config-rule }
+                  dup-config-rule multiple-always-assigns }
 
 group extra = { empty-member empty-stmt dup-import pointless-void-cast case-gen-none case-gen-dup
                 unused-result format-real ignored-slice task-ignored width-trunc dup-attr event-const

scripts/warning_docs.txt

@@ -1162,3 +1162,18 @@ config cfg;
     instance d.foo use baz;
 endconfig
 ```
+
+-Wmultiple-always-assigns
+Detects that variables on the left-hand side of assignments within an procedure blocks,
+including variables from the contents of a called functions, shall not be written to by any other process.
+```
+module m(input clk, input rst);
+    logic i;
+    always_ff @(posedge clk) begin
+        i <= 1;
+    end
+    always_ff @(posedge rst) begin
+        i <= 2;
+    end
+endmodule
+```

source/ast/expressions/CallExpression.cpp

@@ -372,8 +372,7 @@ Expression& CallExpression::fromArgs(Compilation& compilation, const Subroutine&
     // If this subroutine is invoked from a procedure, register drivers for this
     // particular procedure to detect multiple driver violations.
     if (!thisClass) {
-        if (auto proc = context.getProceduralBlock();
-            proc && proc->isSingleDriverBlock() && !context.scope->isUninstantiated()) {
+        if (auto proc = context.getProceduralBlock(); proc && !context.scope->isUninstantiated()) {
             addSubroutineDrivers(*proc, symbol, *result);
         }
     }

tests/unittests/ast/MemberTests.cpp

@@ -1915,7 +1915,7 @@ endmodule
     auto& diags = compilation.getAllDiagnostics();
     std::string result = "\n" + report(diags);
     CHECK(result == R"(
-source:14:17: error: variable 'foo' driven by always_comb procedure cannot be written to by any other process
+source:14:17: warning: variable 'foo' driven by always_comb procedure cannot be written to by any other process [-Wmultiple-always-assigns]
     always_comb i.foo = 1;
                 ^~~~~
 note: from 'm.n2' and 'm.n1'

tests/unittests/ast/SubroutineTests.cpp

@@ -708,3 +708,83 @@ endmodule
     CHECK(diags[0].code == diag::MultipleAlwaysAssigns);
     CHECK(diags[1].code == diag::MultipleAlwaysAssigns);
 }
+
+TEST_CASE("driver checking applied to static function args (always_ff and always_ff)") {
+    auto tree = SyntaxTree::fromText(R"(
+module m(input clk, input rst);
+    function logic f(logic a);
+        logic b;
+        b = a;
+        return b;
+    endfunction
+
+    logic i, j;
+    always_ff @(posedge clk) begin
+        i <= f(i);
+    end
+    always_ff @(posedge rst) begin
+        j <= f(j);
+    end
+endmodule
+)");
+
+    Compilation compilation;
+    compilation.addSyntaxTree(tree);
+
+    auto& diags = compilation.getAllDiagnostics();
+    REQUIRE(diags.size() == 1);
+    CHECK(diags[0].code == diag::MultipleAlwaysAssigns);
+}
+
+TEST_CASE("driver checking applied to static function local variables (always_ff and always)") {
+    auto tree = SyntaxTree::fromText(R"(
+module m(input clk, input rst);
+    function logic f(logic a);
+        logic b;
+        b = a;
+        return b;
+    endfunction
+
+    logic i, j;
+    always @(posedge clk) begin
+        i <= f(i);
+    end
+    always_ff @(posedge rst) begin
+        j <= f(j);
+    end
+endmodule
+)");
+
+    Compilation compilation;
+    compilation.addSyntaxTree(tree);
+
+    auto& diags = compilation.getAllDiagnostics();
+    REQUIRE(diags.size() == 1);
+    CHECK(diags[0].code == diag::MultipleAlwaysAssigns);
+}
+
+TEST_CASE("driver checking applied to static function local variables (always and always)") {
+    auto tree = SyntaxTree::fromText(R"(
+module m(input clk, input rst);
+    function logic f(logic a);
+        logic b;
+        b = a;
+        return b;
+    endfunction
+
+    logic i, j;
+    always @(posedge clk) begin
+        i <= f(i);
+    end
+    always @(posedge rst) begin
+        j <= f(j);
+    end
+endmodule
+)");
+
+    Compilation compilation;
+    compilation.addSyntaxTree(tree);
+
+    auto& diags = compilation.getAllDiagnostics();
+    REQUIRE(diags.size() == 0);
+}