[clang-tools-extra] [clangd] Extract to function: Pass unmodified scalar parameters by value (PR #227675)

[Aleksandr Platonov via cfe-commits]

================
@@ -1014,15 +1014,25 @@ bool createParameters(NewFunction &ExtractedFunc,
       return false;
     // Parameter qualifiers are same as the Decl's qualifiers.
     QualType TypeInfo = VD->getType().getNonReferenceType();
-    // Add const if it's not (conservatively) mutated in the zone: it's
-    // still passed by reference to avoid a copy, but the reference doesn't
-    // need to be mutable. Array types are never made const: mutating array
-    // elements through a non-const-ref loop variable or a decayed pointer
-    // argument is common and easy to miss conservatively, so we don't try.
-    if (!DeclInfo.IsPossiblyMutated && !TypeInfo->isArrayType())
-      TypeInfo.addConst();
     // FIXME: check if parameter will be a non l-value reference.
     bool IsPassedByReference = true;
+    if (!DeclInfo.IsPossiblyMutated) {
+      // A scalar (arithmetic, pointer, enumeration, ...) is at least as
+      // cheap to copy as to pass by reference, and less noisy. Any
+      // pre-existing const is dropped: it's a no-op on a by-value
----------------
ArcsinX wrote:

Unsure that it's right to drop const.

E.g.
```cpp
void bar(int &);
void bar(const int &);

void foo(const int A) {
[[
  bar(A); // calls bar(const int &)
]]
}
```

After extraction:
```cpp
void extracted(int A) {
      bar(A); // calls bar(int &), behavior changed!
}

void foo(const int A) {
  extracted(A);
}
```

https://github.com/llvm/llvm-project/pull/227675