From 7e7d0e1ffaaee4f3deb49d3b98ffd5fcefaf85b1 Mon Sep 17 00:00:00 2001
From: LemonBoy <thatlemon@gmail.com>
Date: Mon, 6 Jan 2020 17:11:10 +0100
Subject: [PATCH] Better handling of decayed arrays to pointers

---
 src-self-hosted/translate_c.zig | 29 +++++++++++++++++++++++++++--
 test/run_translated_c.zig       | 13 +++++++++++++
 2 files changed, 40 insertions(+), 2 deletions(-)

diff --git a/src-self-hosted/translate_c.zig b/src-self-hosted/translate_c.zig
index f14fa00c60..64ea8fa62f 100644
--- a/src-self-hosted/translate_c.zig
+++ b/src-self-hosted/translate_c.zig
@@ -1334,9 +1334,22 @@ fn transImplicitCastExpr(
         .BitCast, .FloatingCast, .FloatingToIntegral, .IntegralToFloating, .IntegralCast, .PointerToIntegral, .IntegralToPointer => {
             return transCCast(rp, scope, ZigClangImplicitCastExpr_getBeginLoc(expr), dest_type, src_type, sub_expr_node);
         },
-        .LValueToRValue, .NoOp, .FunctionToPointerDecay, .ArrayToPointerDecay => {
+        .LValueToRValue, .NoOp, .FunctionToPointerDecay => {
             return maybeSuppressResult(rp, scope, result_used, sub_expr_node);
         },
+        .ArrayToPointerDecay => {
+            switch (ZigClangExpr_getStmtClass(sub_expr)) {
+                .StringLiteralClass, .PredefinedExprClass => {
+                    return maybeSuppressResult(rp, scope, result_used, sub_expr_node);
+                },
+                else => {
+                    const prefix_op = try transCreateNodePrefixOp(rp.c, .AddressOf, .Ampersand, "&");
+                    prefix_op.rhs = sub_expr_node;
+
+                    return maybeSuppressResult(rp, scope, result_used, &prefix_op.base);
+                },
+            }
+        },
         .NullToPointer => {
             return try transCreateNodeNullLiteral(rp.c);
         },
@@ -2469,7 +2482,19 @@ fn transMemberExpr(rp: RestorePoint, scope: *Scope, stmt: *const ZigClangMemberE
 }
 
 fn transArrayAccess(rp: RestorePoint, scope: *Scope, stmt: *const ZigClangArraySubscriptExpr, result_used: ResultUsed) TransError!*ast.Node {
-    const container_node = try transExpr(rp, scope, ZigClangArraySubscriptExpr_getBase(stmt), .used, .r_value);
+    var base_stmt = ZigClangArraySubscriptExpr_getBase(stmt);
+
+    // Unwrap the base statement if it's an array decayed to a bare pointer type
+    // so that we index the array itself
+    if (ZigClangStmt_getStmtClass(@ptrCast(*const ZigClangStmt, base_stmt)) == .ImplicitCastExprClass) {
+        const implicit_cast = @ptrCast(*const ZigClangImplicitCastExpr, base_stmt);
+
+        if (ZigClangImplicitCastExpr_getCastKind(implicit_cast) == .ArrayToPointerDecay) {
+            base_stmt = ZigClangImplicitCastExpr_getSubExpr(implicit_cast);
+        }
+    }
+
+    const container_node = try transExpr(rp, scope, base_stmt, .used, .r_value);
     const node = try transCreateNodeArrayAccess(rp.c, container_node);
     node.op.ArrayAccess = try transExpr(rp, scope, ZigClangArraySubscriptExpr_getIdx(stmt), .used, .r_value);
     node.rtoken = try appendToken(rp.c, .RBrace, "]");
diff --git a/test/run_translated_c.zig b/test/run_translated_c.zig
index 3ebc4b127c..0b11018118 100644
--- a/test/run_translated_c.zig
+++ b/test/run_translated_c.zig
@@ -70,4 +70,17 @@ pub fn addCases(cases: *tests.RunTranslatedCContext) void {
         \\    return 0;
         \\}
     , "");
+
+    cases.add("array to pointer decay",
+        \\#include <stdlib.h>
+        \\int main(int argc, char **argv) {
+        \\    char data[3] = {'a','b','c'};
+        \\    if (2[data] != data[2]) abort();
+        \\    if ("abc"[1] != data[1]) abort();
+        \\    char *as_ptr = data;
+        \\    if (2[as_ptr] != as_ptr[2]) abort();
+        \\    if ("abc"[1] != as_ptr[1]) abort();
+        \\    return 0;
+        \\}
+    , "");
 }