produce else if chain expression instead of nested if expression. fix #…

…769

c2rust-transpile/src/cfg/inc_cleanup.rs

@@ -127,21 +127,34 @@ fn cleanup_if(stmt: Stmt) -> Stmt {
     if let Stmt::Expr(Expr::If(ExprIf {
         cond,
         then_branch,
-        else_branch: Some((_token, else_)),
+        else_branch: Some((token, else_)),
         ..
     })) = &stmt
     {
         match &**else_ {
             Expr::Block(ExprBlock {
                 block, label: None, ..
-            }) if block.stmts.is_empty() => {
-                return Stmt::Expr(Expr::If(ExprIf {
-                    cond: cond.clone(),
-                    then_branch: then_branch.clone(),
-                    else_branch: Default::default(),
-                    attrs: Default::default(),
-                    if_token: Default::default(),
-                }));
+            }) => {
+                if block.stmts.is_empty() {
+                    return Stmt::Expr(Expr::If(ExprIf {
+                        cond: cond.clone(),
+                        then_branch: then_branch.clone(),
+                        else_branch: Default::default(),
+                        attrs: Default::default(),
+                        if_token: Default::default(),
+                    }));
+                } else if block.stmts.len() == 1 {
+                    // flatten nested if expression to else if chain
+                    if let Stmt::Expr(Expr::If(nested_if_expr)) = &block.stmts[0] {
+                        return Stmt::Expr(Expr::If(ExprIf {
+                            cond: cond.clone(),
+                            then_branch: then_branch.clone(),
+                            else_branch: Some((*token, Box::new(Expr::If(nested_if_expr.clone())))),
+                            attrs: Default::default(),
+                            if_token: Default::default(),
+                        }));
+                    }
+                }
             }
             _ => {}
         }

tests/conditionals/src/else_if_chain.c

@@ -0,0 +1,13 @@
+// should produce else if chain
+int entry4(int i)
+{
+    if (i == 0){
+        return 0;
+    }else if (i == 10){
+        return 10;
+    }else if (i == 20){
+        return 20;
+    }
+
+    return -1;
+}

tests/conditionals/src/test_conditionals.rs

@@ -4,6 +4,7 @@ use crate::conditionals::{rust_entry2, rust_ternaries};
 use crate::unused_conditionals::{
     rust_unused_conditional1, rust_unused_conditional2, rust_unused_conditional3,
 };
+use crate::else_if_chain::rust_entry4;
 use libc::{c_int, c_uint};
 
 #[link(name = "test")]
@@ -13,6 +14,8 @@ extern "C" {
     fn entry2(_: c_uint, _: *mut c_int);
 
     fn entry3(_: c_uint, _: *mut c_int);
+
+    fn entry4(_: c_int) -> c_int;
 
     fn unused_conditional1() -> c_int;
     fn unused_conditional2() -> c_int;
@@ -74,3 +77,12 @@ pub fn test_unused_conditional() {
         assert_eq!(unused_conditional3(), rust_unused_conditional3());
     }
 }
+
+pub fn test_else_if_chain(){
+    unsafe {
+        assert_eq!(entry4(0) , rust_entry4(0));
+        assert_eq!(entry4(10) , rust_entry4(10));
+        assert_eq!(entry4(20) , rust_entry4(20));
+        assert_eq!(entry4(30) , rust_entry4(30));
+    }
+}