Improve diagnostics for StructExpression (#4357)

* Improve diagnostics for StructExpression
* Move function def to expression.def.
* Properly initialize empty cstring.

backends/p4tools/p4tools.def

@@ -208,7 +208,7 @@ public:
     inline cstring concolicMethodName = "";
 
     toString {
-        cstring argumentStr;
+        cstring argumentStr = "";
         cstring sep = "";
         for (const auto *arg : *arguments) {
             argumentStr += sep + arg->toString();

ir/expression.def

@@ -482,6 +482,18 @@ class StructExpression : Expression {
         size_t size = components.size();
         return components.at(size - 1)->is<IR::NamedDots>();
     }
+    toString {
+        cstring str = "{";
+        if (!components.empty()) {
+            cstring exprStr = components.at(0)->expression->toString();
+            str += " " + components.at(0)->toString() + " = " + exprStr;
+        }
+        for (unsigned i = 1; i < size(); i++) {
+            cstring exprStr = components.at(i)->expression->toString();
+            str += ", " + components.at(i)->toString() + " = " + exprStr;
+        }
+        return str + " }";
+    }
 }
 
 /// Can be an invalid header or header_union

testdata/p4_16_errors_outputs/issue2220.p4-stderr

@@ -1,4 +1,4 @@
-issue2220.p4(11): [--Werror=type-error] error: StructExpression: values of type 'bit<8>' cannot be implicitly cast to type 'myEnum'
+issue2220.p4(11): [--Werror=type-error] error: { val = 8w0 }: values of type 'bit<8>' cannot be implicitly cast to type 'myEnum'
  S s1 = { val = (bit<8>)0 };
         ^^^^^^^^^^^^^^^^^^^
 issue2220.p4(3)

testdata/p4_16_errors_outputs/issue3671-2.p4-stderr

@@ -1,4 +1,4 @@
-issue3671-2.p4(17): [--Werror=type-error] error: StructExpression: argument does not match declaration in actions list: StructExpression
+issue3671-2.p4(17): [--Werror=type-error] error: { f1 = ext1, f0 = ext2 }: argument does not match declaration in actions list: { f0 = ext1, f1 = ext2 }
         default_action = a1({f1 = ext1(),f0 = ext2()});
                             ^^^^^^^^^^^^^^^^^^^^^^^^^
 issue3671-2.p4(15)

testdata/p4_16_errors_outputs/structure-valued-expr-errs-1.p4-stderr

@@ -169,7 +169,7 @@ structure-valued-expr-errs-1.p4(31)
   header h1_t {
          ^^^^
   ---- Originating from:
-structure-valued-expr-errs-1.p4(112): Source expression 'StructExpression' produces a result of type 'unknown struct' which cannot be assigned to a left-value with type 'header h1_t'
+structure-valued-expr-errs-1.p4(112): Source expression '{ f2 = 5, f1 = 2 }' produces a result of type 'unknown struct' which cannot be assigned to a left-value with type 'header h1_t'
               hdr.h1 = {f2=5, f1=2};
                        ^^^^^^^^^^^^
 structure-valued-expr-errs-1.p4(112)
@@ -186,7 +186,7 @@ structure-valued-expr-errs-1.p4(32): No initializer for field f1
       bit<8> f1;
              ^^
   ---- Originating from:
-structure-valued-expr-errs-1.p4(113): Source expression 'StructExpression' produces a result of type 'unknown struct' which cannot be assigned to a left-value with type 'header h1_t'
+structure-valued-expr-errs-1.p4(113): Source expression '{ f2 = 5 }' produces a result of type 'unknown struct' which cannot be assigned to a left-value with type 'header h1_t'
               hdr.h1 = {f2=5};
                        ^^^^^^
 structure-valued-expr-errs-1.p4(113)
@@ -206,7 +206,7 @@ structure-valued-expr-errs-1.p4(43)
   struct s1_t {
          ^^^^
   ---- Originating from:
-structure-valued-expr-errs-1.p4(114): Source expression 'StructExpression' produces a result of type 'unknown struct' which cannot be assigned to a left-value with type 'struct s1_t'
+structure-valued-expr-errs-1.p4(114): Source expression '{ f2 = 5, f1 = 2 }' produces a result of type 'unknown struct' which cannot be assigned to a left-value with type 'struct s1_t'
               hdr.hstructs.s1 = {f2=5, f1=2};
                                 ^^^^^^^^^^^^
 structure-valued-expr-errs-1.p4(114)
@@ -223,7 +223,7 @@ structure-valued-expr-errs-1.p4(44): No initializer for field f1
       bit<8> f1;
              ^^
   ---- Originating from:
-structure-valued-expr-errs-1.p4(115): Source expression 'StructExpression' produces a result of type 'unknown struct' which cannot be assigned to a left-value with type 'struct s1_t'
+structure-valued-expr-errs-1.p4(115): Source expression '{ f2 = 5 }' produces a result of type 'unknown struct' which cannot be assigned to a left-value with type 'struct s1_t'
               hdr.hstructs.s1 = {f2=5};
                                 ^^^^^^
 structure-valued-expr-errs-1.p4(115)
@@ -243,7 +243,7 @@ structure-valued-expr-errs-1.p4(35)
   header h2_t {
          ^^^^
   ---- Originating from:
-structure-valued-expr-errs-1.p4(120): Source expression 'StructExpression' produces a result of type 'unknown struct' which cannot be assigned to a left-value with type 'header h2_t'
+structure-valued-expr-errs-1.p4(120): Source expression '{ f2 = 5 }' produces a result of type 'unknown struct' which cannot be assigned to a left-value with type 'header h2_t'
               hdr.h2 = {f2=5};
                        ^^^^^^
 structure-valued-expr-errs-1.p4(120)
@@ -263,7 +263,7 @@ structure-valued-expr-errs-1.p4(47)
   struct s2_t {
          ^^^^
   ---- Originating from:
-structure-valued-expr-errs-1.p4(121): Source expression 'StructExpression' produces a result of type 'unknown struct' which cannot be assigned to a left-value with type 'struct s2_t'
+structure-valued-expr-errs-1.p4(121): Source expression '{ f2 = 5 }' produces a result of type 'unknown struct' which cannot be assigned to a left-value with type 'struct s2_t'
               hdr.hstructs.s2 = {f2=5};
                                 ^^^^^^
 structure-valued-expr-errs-1.p4(121)