Support switch statements

This is relatively simple and straightforward.

Note that this is much more permissive than GLSL compilers seem to be;
for example I'm pretty sure this will allow much more in a case label
than it should (I think a literal int must come after). But I don't
think it will cause the minifier to emit invalid GLSL unless the input
was invalid already.

It's actually somewhat unclear what the right grammar even is here.
Looking at the 4.5 spec linked in laurentlb#18 -- section 9 (the normative
grammar), page 205 says that a `case_label` is `CASE expression COLON`,
but from testing with an actual compiler it looks like it needs to be a
literal integer. Also the definition of `switch_statement_list` doesn't
include `case_label`.  So by my reading that's a bug in the spec (or at
least a place that compilers are quite reasonably more restrictive) so
even if we did want to be perfectly correct here I'm not sure what
exactly that looks like :)

Fixes laurentlb#18.

src/ast.fs

@@ -82,6 +82,11 @@ and Stmt =
     | DoWhile of Expr * Stmt
     | Jump of JumpKeyword * Expr option (*break, continue, return (expr)?, discard*)
     | Verbatim of string
+    | Switch of Expr * (CaseLabel * Stmt list) list
+
+and CaseLabel =
+    | Case of Expr
+    | Default
 
 and FunctionType = {
     retType: Type (*return*)
@@ -184,6 +189,14 @@ let rec mapStmt env i =
         | Jump(k, e) ->
             env, Jump (k, Option.map (mapExpr env) e)
         | Verbatim _ as v -> env, v
+        | Switch(e, cl) ->
+            let mapLabel = function
+                | Case e -> Case (mapExpr env e)
+                | Default -> Default
+            let mapCase (l, sl) =
+                let _, sl = foldList env mapStmt sl
+                (mapLabel l, sl)
+            env, Switch (mapExpr env e, List.map mapCase cl)
     let env, res = aux i
     env, env.fStmt res
 

src/parse.fs

@@ -5,7 +5,6 @@ open Options.Globals
 module private ParseImpl =
 
     // TODO: true, false
-    // TODO: switch case
 
     open FParsec.Primitives
     open FParsec.CharParsers
@@ -280,6 +279,18 @@ module private ParseImpl =
         let list = many statement |>> Ast.Block
         between (ch '{') (ch '}') list
 
+    let caseLabel =
+        let keywCase = keyword "case" >>. expr |>> (fun e -> Ast.Case e)
+        let keywDefault = keyword "default" |>> (fun _ -> Ast.Default)
+        attempt keywCase <|> keywDefault .>> ch ':'
+
+    let case =
+        pipe2 caseLabel (many (attempt statement)) (fun l sl -> (l, sl))
+
+    let switch =
+      let body = between (ch '{') (ch '}') (many case)
+      pipe2 (keyword "switch" >>. parenExp) body (fun e cl -> Ast.Switch(e, cl))
+
     let mutable private forbiddenNames = []
 
     let macro =
@@ -316,6 +327,7 @@ module private ParseImpl =
         ifStatement
         whileLoop
         doWhileLoop
+        switch
         verbatim |>> Ast.Verbatim
         macro |>> Ast.Verbatim
         attribute |>> Ast.Verbatim

src/printer.fs

@@ -215,6 +215,15 @@ module private PrinterImpl =
             let s = if System.Char.IsLetterOrDigit s.[s.Length - 1] then s + " " else s
             if s <> "" && s.[0] = '#' then out "%s%s" (backslashN()) (escape s)
             else escape s
+        | Switch(e, cl) ->
+            let labelToS = function
+                | Case e -> out "case %s:" (exprToS e)
+                | Default -> out "default:"
+            let caseToS (l, sl) =
+                let stmts = List.map (stmtToS (indent+2)) sl |> String.concat ""
+                out "%s%s%s" (nl (indent+1)) (labelToS l) stmts
+            let body = List.map caseToS cl |> String.concat ""
+            out "%s(%s){%s%s}" "switch" (exprToS e) body (nl indent)
 
     and stmtToS indent i =
         out "%s%s" (nl indent) (stmtToS' indent i)

src/renamer.fs

@@ -311,6 +311,17 @@ module private RenamerImpl =
             env
         | Jump(_, e) -> renOpt e; env
         | Verbatim _ -> env
+        | Switch(e, cl) ->
+            let renLabel = function
+                | Case e -> renExpr env e
+                | Default -> ()
+            let renCase env (l, sl) =
+                renLabel l
+                renList env renStmt sl |> ignore<Env>
+                env
+            renExpr env e
+            renList env renCase cl |> ignore<Env>
+            env
 
     let rec renTopLevelName env = function
         | TLDecl d -> renDecl true env d

src/rewriter.fs

@@ -204,7 +204,7 @@ let findInlinable block =
                     localDefs.[def.name.Name] <- (def.name, deps.Count > 0)
         | Expr e
         | Jump (_, Some e) -> localExpr <- e :: localExpr
-        | Verbatim _ | Jump (_, None) | Block _ | If _| ForE _ | ForD _ | While _ | DoWhile _ -> ()
+        | Verbatim _ | Jump (_, None) | Block _ | If _| ForE _ | ForD _ | While _ | DoWhile _ | Switch _ -> ()
 
     let localReferences = collectReferences (List.map Expr localExpr)
     let allReferences = collectReferences block

tests/commands.txt

@@ -39,6 +39,7 @@
 -o tests/unit/function_overload.expected tests/unit/function_overload.frag
 -o tests/unit/externals.expected tests/unit/externals.frag
 -o tests/unit/macros.expected --no-inlining tests/unit/macros.frag
+--format indented -o tests/unit/switch.expected tests/unit/switch.frag
 
 # Optimization tests
 

tests/unit/switch.expected

@@ -0,0 +1,45 @@
+void h()
+{
+  switch(42){
+    case 42:
+      break;
+  }
+}
+
+#define GOOD 42
+
+void i()
+{
+  switch(42){
+    case GOOD:
+      break;
+  }
+}
+void h(in int i)
+{
+  switch(i){
+    case 0:
+      break;
+  }
+}
+void i(in int i)
+{
+  switch(i+42){
+    case 0:
+      break;
+  }
+}
+float G()
+{
+  switch(42){
+    case 42:
+      float i=4.2;
+      float k=2.4;
+      return i+k;
+    case 43:
+      float i=4.3;
+      return i+3.4;
+    default:
+      return 0.;
+  }
+}

tests/unit/switch.frag

@@ -0,0 +1,42 @@
+void switchConst() {
+  switch (42) {
+    case 42:
+      break;
+  }
+}
+
+#define GOOD 42
+void switchDefine() {
+  switch (42) {
+    case GOOD:
+      break;
+  }
+}
+
+void switchArg(in int someArg) {
+  switch (someArg) {
+    case 0:
+      break;
+  }
+}
+
+void switchExpr(in int someArg) {
+  switch (someArg + 42) {
+    case 0:
+      break;
+  }
+}
+
+float switchMultiple() {
+  switch (42) {
+    case 42:
+      float someVar = 4.2;
+      float otherVar = 2.4;
+      return someVar + otherVar;
+    case 43:
+      float someVar = 4.3;
+      return someVar + 3.4;
+    default:
+      return 0.0;
+  }
+}