From 9b358efea13017f3e033acce9c4a2c6c947d9a4d Mon Sep 17 00:00:00 2001
From: Dzmitry Malyshau <kvark@fastmail.com>
Date: Thu, 11 Feb 2021 16:41:09 -0500
Subject: [PATCH] [wgsl] support 'elseif' construct

---
 src/front/wgsl/mod.rs   | 20 +++++++++++++++++++-
 src/front/wgsl/tests.rs |  5 +++++
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/src/front/wgsl/mod.rs b/src/front/wgsl/mod.rs
index 38aaf4095b..c2bb94e922 100644
--- a/src/front/wgsl/mod.rs
+++ b/src/front/wgsl/mod.rs
@@ -1669,11 +1669,29 @@ impl Parser {
                 lexer.expect(Token::Paren(')'))?;
 
                 let accept = self.parse_block(lexer, context.reborrow(), false)?;
-                let reject = if lexer.skip(Token::Word("else")) {
+                let mut elsif_stack = Vec::new();
+                while lexer.skip(Token::Word("elseif")) {
+                    lexer.expect(Token::Paren('('))?;
+                    let other_condition =
+                        self.parse_general_expression(lexer, context.as_expression())?;
+                    lexer.expect(Token::Paren(')'))?;
+                    let other_block = self.parse_block(lexer, context.reborrow(), false)?;
+                    elsif_stack.push((other_condition, other_block));
+                }
+                let mut reject = if lexer.skip(Token::Word("else")) {
                     self.parse_block(lexer, context.reborrow(), false)?
                 } else {
                     Vec::new()
                 };
+                // reverse-fold the else-if blocks
+                //Note: we may consider uplifting this to the IR
+                for (other_cond, other_block) in elsif_stack.drain(..).rev() {
+                    reject = vec![crate::Statement::If {
+                        condition: other_cond,
+                        accept: other_block,
+                        reject,
+                    }];
+                }
 
                 Some(crate::Statement::If {
                     condition,
diff --git a/src/front/wgsl/tests.rs b/src/front/wgsl/tests.rs
index c0408415e1..4fdfc1088b 100644
--- a/src/front/wgsl/tests.rs
+++ b/src/front/wgsl/tests.rs
@@ -104,6 +104,11 @@ fn parse_if() {
                 discard;
             } else {}
             if (0 != 1) {}
+            if (false) {
+                return;
+            } elseif (true) {
+                return;
+            } else {}
         }
     ",
     )