Improve error reporting for invalid var-decls.

We now interpret any statement of the form `Type identifier...` as a
var-declaration and report errors as such. Previously, if a var-decl
statement generated an error during parse, we'd report errors as if it
were an expression-statement, which meant that slightly-invalid code
could return out-of-context, misleading errors.

Bug: skia:11287
Change-Id: I2c6cf2984760eb34593c80cb30f8c4e007d42027
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/370036
Commit-Queue: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>

gn/sksl_tests.gni

@@ -131,6 +131,7 @@ sksl_error_tests = [
   "/sksl/errors/OverflowIntLiteral.sksl",
   "/sksl/errors/OverflowParamArraySize.sksl",
   "/sksl/errors/OverflowUintLiteral.sksl",
+  "/sksl/errors/PrototypeInFuncBody.sksl",
   "/sksl/errors/PrivateTypes.sksl",
   "/sksl/errors/RedeclareBasicType.sksl",
   "/sksl/errors/RedeclareEnum.sksl",

resources/sksl/errors/PrototypeInFuncBody.sksl

@@ -0,0 +1,3 @@
+void main() {
+    float x();
+}

src/sksl/SkSLParser.cpp

@@ -534,9 +534,9 @@ ASTNode::ID Parser::varDeclarationsOrExpressionStatement() {
         // occasionally the type is part of a constructor, and these are actually expression-
         // statements in disguise. First, attempt the common case: parse it as a vardecl.
         Checkpoint checkpoint(this);
-        ASTNode::ID node = this->varDeclarations();
-        if (node) {
-            return node;
+        VarDeclarationsPrefix prefix;
+        if (this->varDeclarationsPrefix(&prefix)) {
+            return this->varDeclarationEnd(prefix.modifiers, prefix.type, this->text(prefix.name));
         }
 
         // If this statement wasn't actually a vardecl after all, rewind and try parsing it as an
@@ -547,19 +547,24 @@ ASTNode::ID Parser::varDeclarationsOrExpressionStatement() {
     return this->expressionStatement();
 }
 
+// Helper function for varDeclarations(). If this function succeeds, we assume that the rest of the
+// statement is a variable-declaration statement, not an expression-statement.
+bool Parser::varDeclarationsPrefix(VarDeclarationsPrefix* prefixData) {
+    prefixData->modifiers = this->modifiers();
+    prefixData->type = this->type();
+    if (!prefixData->type) {
+        return false;
+    }
+    return this->expectIdentifier(&prefixData->name);
+}
+
 /* modifiers type IDENTIFIER varDeclarationEnd */
 ASTNode::ID Parser::varDeclarations() {
-    Checkpoint checkpoint(this);
-    Modifiers modifiers = this->modifiers();
-    ASTNode::ID type = this->type();
-    if (!type) {
+    VarDeclarationsPrefix prefix;
+    if (!this->varDeclarationsPrefix(&prefix)) {
         return ASTNode::ID::Invalid();
     }
-    Token name;
-    if (!this->expectIdentifier(&name)) {
-        return ASTNode::ID::Invalid();
-    }
-    return this->varDeclarationEnd(modifiers, type, this->text(name));
+    return this->varDeclarationEnd(prefix.modifiers, prefix.type, this->text(prefix.name));
 }
 
 /* STRUCT IDENTIFIER LBRACE varDeclaration* RBRACE */

src/sksl/SkSLParser.h

@@ -172,6 +172,14 @@ private:
 
     ASTNode::ID declaration();
 
+    struct VarDeclarationsPrefix {
+        Modifiers modifiers;
+        ASTNode::ID type;
+        Token name;
+    };
+
+    bool varDeclarationsPrefix(VarDeclarationsPrefix* prefixData);
+
     ASTNode::ID varDeclarationsOrExpressionStatement();
 
     ASTNode::ID varDeclarations();

tests/sksl/errors/PrototypeInFuncBody.glsl

@@ -0,0 +1,4 @@
+### Compilation failed:
+
+error: 2: expected ';', but found '('
+1 error