diff options
Diffstat (limited to 'source/slang/check.cpp')
| -rw-r--r-- | source/slang/check.cpp | 60 |
1 files changed, 59 insertions, 1 deletions
diff --git a/source/slang/check.cpp b/source/slang/check.cpp index 5fd8be2d5..6f9aa8adc 100644 --- a/source/slang/check.cpp +++ b/source/slang/check.cpp @@ -204,6 +204,19 @@ namespace Slang expr->BaseExpression = baseExpr; expr->name = declRef.GetName(); expr->declRef = declRef; + + // When referring to a member through an expression, + // the result is only an l-value if both the base + // expression and the member agree that it should be. + // + // We have already used the `QualType` from the member + // above (that is `type`), so we need to take the + // l-value status of the base expression into account now. + if(!baseExpr->type.IsLeftValue) + { + expr->type.IsLeftValue = false; + } + return expr; } } @@ -3991,6 +4004,46 @@ namespace Slang else { getSink()->diagnose(expr, Diagnostics::assignNonLValue); + + // As a special case, check if the LHS expression is derived + // from a `this` parameter (implicitly or explicitly), which + // is immutable. We can give the user a bit more context into + // what is going on. + // + // We will try to handle expressions of the form: + // + // e ::= "this" + // | e . name + // | e [ expr ] + // + // We will unwrap the `e.name` and `e[expr]` cases in a loop. + RefPtr<Expr> e = expr->left; + for(;;) + { + if(auto memberExpr = e.As<MemberExpr>()) + { + e = memberExpr->BaseExpression; + } + else if(auto subscriptExpr = e.As<IndexExpr>()) + { + e = subscriptExpr->BaseExpression; + } + else + { + break; + } + } + // + // Now we check to see if we have a `this` expression, + // and if it is immutable. + if(auto thisExpr = e.As<ThisExpr>()) + { + if(!thisExpr->type.IsLeftValue) + { + getSink()->diagnose(thisExpr, Diagnostics::thisIsImmutableByDefault); + } + } + } } expr->type = type; @@ -7800,7 +7853,12 @@ namespace Slang { QualType qualType; qualType.type = GetType(varDeclRef); - qualType.IsLeftValue = true; // TODO(tfoley): allow explicit `const` or `let` variables + + bool isLValue = true; + if(varDeclRef.getDecl()->FindModifier<ConstModifier>()) + isLValue = false; + + qualType.IsLeftValue = isLValue; return qualType; } else if (auto typeAliasDeclRef = declRef.As<TypeDefDecl>()) |