Fix 20334: ImportC: enums created from string literal #defines don’t implicitly convert to const(char)* in D. (#21193)

Fixes: https://github.com/dlang/dmd/issues/20334

After preprocessing, #defines in C code that are just string literals
are converted into D enums. As these are collected for use in D code,
they should behave like D string literals and not C string literals.

compiler/src/dmd/astbase.d

@@ -4954,6 +4954,8 @@ struct ASTBase
 
         /// If the string is parsed from a hex string literal
         bool hexString = false;
+        /// If the string is from a collected C macro
+        bool cMacro = false;
 
         extern (D) this(Loc loc, const(void)[] string)
         {
@@ -4963,13 +4965,14 @@ struct ASTBase
             this.sz = 1;                    // work around LDC bug #1286
         }
 
-        extern (D) this(Loc loc, const(void)[] string, size_t len, ubyte sz, char postfix = 0)
+        extern (D) this(Loc loc, const(void)[] string, size_t len, ubyte sz, char postfix = 0, bool cMacro=false)
         {
             super(loc, EXP.string_, __traits(classInstanceSize, StringExp));
             this.string = cast(char*)string;
             this.len = len;
             this.postfix = postfix;
             this.sz = 1;                    // work around LDC bug #1286
+            this.cMacro = cMacro;
         }
 
         /**********************************************

compiler/src/dmd/cparse.d

@@ -6193,7 +6193,7 @@ final class CParser(AST) : Parser!AST
                                 /* Declare manifest constant:
                                  *  enum id = "string";
                                  */
-                                AST.Expression e = new AST.StringExp(scanloc, str[0 .. len], len, 1, postfix);
+                                AST.Expression e = new AST.StringExp(scanloc, str[0 .. len], len, 1, postfix, true);
                                 auto v = new AST.VarDeclaration(scanloc, null, id, new AST.ExpInitializer(scanloc, e), STC.manifest);
                                 addSym(v);
                                 ++p;

compiler/src/dmd/expression.d

@@ -1406,6 +1406,8 @@ extern (C++) final class StringExp : Expression
 
     /// If the string is parsed from a hex string literal
     bool hexString = false;
+    /// If the string is from a collected C macro
+    bool cMacro = false;
 
     enum char NoPostfix = 0;
 
@@ -1417,13 +1419,14 @@ extern (C++) final class StringExp : Expression
         this.sz = 1;                    // work around LDC bug #1286
     }
 
-    extern (D) this(Loc loc, const(void)[] string, size_t len, ubyte sz, char postfix = NoPostfix) scope
+    extern (D) this(Loc loc, const(void)[] string, size_t len, ubyte sz, char postfix = NoPostfix, bool cMacro = false) scope
     {
         super(loc, EXP.string_);
         this.string = cast(char*)string.ptr; // note that this.string should be const
         this.len = len;
         this.sz = sz;
         this.postfix = postfix;
+        this.cMacro = cMacro;
     }
 
     static StringExp create(Loc loc, const(char)* s)

compiler/src/dmd/expression.h

@@ -353,6 +353,7 @@ public:
     unsigned char sz;   // 1: char, 2: wchar, 4: dchar
     d_bool committed;   // if type is committed
     d_bool hexString;   // if string is parsed from a hex string literal
+    d_bool cMacro;      // If the string is from a collected C macro
 
     static StringExp *create(Loc loc, const char *s);
     static StringExp *create(Loc loc, const void *s, d_size_t len);

compiler/src/dmd/expressionsem.d

@@ -4429,7 +4429,7 @@ private extern (C++) final class ExpressionSemanticVisitor : Visitor
             }
             buffer.write4(0);
             e.setData(buffer.extractData(), newlen, 4);
-            if (sc && sc.inCfile)
+            if (!e.cMacro && sc && sc.inCfile)
                 e.type = Type.tuns32.sarrayOf(e.len + 1);
             else
                 e.type = Type.tdchar.immutableOf().arrayOf();
@@ -4454,7 +4454,7 @@ private extern (C++) final class ExpressionSemanticVisitor : Visitor
             }
             buffer.writeUTF16(0);
             e.setData(buffer.extractData(), newlen, 2);
-            if (sc && sc.inCfile)
+            if (!e.cMacro && sc && sc.inCfile)
                 e.type = Type.tuns16.sarrayOf(e.len + 1);
             else
                 e.type = Type.twchar.immutableOf().arrayOf();
@@ -4466,7 +4466,7 @@ private extern (C++) final class ExpressionSemanticVisitor : Visitor
             goto default;
 
         default:
-            if (sc && sc.inCfile)
+            if (!e.cMacro && sc && sc.inCfile)
                 e.type = Type.tchar.sarrayOf(e.len + 1);
             else
                 e.type = Type.tchar.immutableOf().arrayOf();

compiler/src/dmd/frontend.h

@@ -3608,6 +3608,7 @@ public:
     uint8_t sz;
     bool committed;
     bool hexString;
+    bool cMacro;
     enum : char { NoPostfix = 0u };
 
     static StringExp* create(Loc loc, const char* s);
@@ -5548,7 +5549,7 @@ private:
         char realexp[48LLU];
         char complexexp[64LLU];
         char symoffexp[56LLU];
-        char stringexp[43LLU];
+        char stringexp[44LLU];
         char arrayliteralexp[40LLU];
         char assocarrayliteralexp[48LLU];
         char structliteralexp[64LLU];

compiler/test/compilable/imports/imp20344.c

@@ -0,0 +1,2 @@
+// https://github.com/dlang/dmd/issues/20334
+#define X "X"

compiler/test/compilable/test20344.d

@@ -0,0 +1,14 @@
+// https://github.com/dlang/dmd/issues/20334
+// EXTRA_FILES: imports/imp20344.c
+import imports.imp20344;
+string s = X;
+const(char)* p = X;
+
+void takes_string(string){ }
+void takes_char_star(const(char)*){ }
+
+
+void test20344(){
+    takes_string(X);
+    takes_char_star(X);
+}