Generate more diagnostics from IRGenerator, when given bad code.

Two minor changes:
- Converting a Block with bad statements will now generate a partial
  block instead of nullptr.

The change mirrors how DSL behaves; functions containing invalid
statements will now be created and added to the program. Previously, we
would discard a function definition with any invalid statements inside;
this prevented duplicate-function-definition errors from appearing.

- Converting a return with a bad expression will now generate a
  poisoned return instead of nullptr.

This change improves diagnostics for functions with invalid return
statements. If we eliminate the return statements (by returning null),
we report bad return statements as "function can exit without returning
a value" (which is confusing).

Change-Id: I6d998d5c50585f8d96bb7e3cb7f59b63125d6a62
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/446325
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>

src/sksl/SkSLIRGenerator.cpp

@@ -47,6 +47,7 @@
 #include "src/sksl/ir/SkSLInterfaceBlock.h"
 #include "src/sksl/ir/SkSLMethodReference.h"
 #include "src/sksl/ir/SkSLNop.h"
+#include "src/sksl/ir/SkSLPoison.h"
 #include "src/sksl/ir/SkSLPostfixExpression.h"
 #include "src/sksl/ir/SkSLPrefixExpression.h"
 #include "src/sksl/ir/SkSLReturnStatement.h"
@@ -141,10 +142,9 @@ std::unique_ptr<Block> IRGenerator::convertBlock(const ASTNode& block) {
     StatementArray statements;
     for (const auto& child : block) {
         std::unique_ptr<Statement> statement = this->convertStatement(child);
-        if (!statement) {
+        if (statement) {
-            return nullptr;
+            statements.push_back(std::move(statement));
         }
-        statements.push_back(std::move(statement));
     }
     return Block::Make(block.fOffset, std::move(statements), fSymbolTable);
 }
@@ -518,14 +518,14 @@ std::unique_ptr<Statement> IRGenerator::convertReturn(int offset,
 std::unique_ptr<Statement> IRGenerator::convertReturn(const ASTNode& r) {
     SkASSERT(r.fKind == ASTNode::Kind::kReturn);
     if (r.begin() != r.end()) {
-        std::unique_ptr<Expression> value = this->convertExpression(*r.begin());
+        if (std::unique_ptr<Expression> value = this->convertExpression(*r.begin())) {
-        if (!value) {
+            return this->convertReturn(r.fOffset, std::move(value));
-            return nullptr;
+        } else {
+            return this->convertReturn(r.fOffset, Poison::Make(r.fOffset, fContext));
         }
-        return this->convertReturn(r.fOffset, std::move(value));
-    } else {
-        return this->convertReturn(r.fOffset, /*result=*/nullptr);
     }
+
+    return this->convertReturn(r.fOffset, /*result=*/nullptr);
 }
 
 std::unique_ptr<Statement> IRGenerator::convertBreak(const ASTNode& b) {

tests/sksl/errors/MismatchedNumbers.glsl

@@ -5,7 +5,9 @@ error: 29: type mismatch: '=' cannot operate on 'uint', 'float'
 error: 30: type mismatch: '=' cannot operate on 'int', 'uint'
 error: 31: type mismatch: '=' cannot operate on 'int', 'float'
 error: 32: type mismatch: '=' cannot operate on 'float', 'int'
+error: 32: function 'f_eq_i_disallowed' can exit without returning a value
 error: 33: type mismatch: '=' cannot operate on 'float', 'uint'
+error: 33: function 'f_eq_u_disallowed' can exit without returning a value
 error: 34: type mismatch: '=' cannot operate on 'uint', 'int'
 error: 35: type mismatch: '=' cannot operate on 'uint', 'float'
 error: 36: type mismatch: '+' cannot operate on 'int', 'float'
@@ -48,4 +50,4 @@ error: 72: type mismatch: '+' cannot operate on 'uint', 'int'
 error: 73: type mismatch: '-' cannot operate on 'uint', 'int'
 error: 74: type mismatch: '*' cannot operate on 'uint', 'int'
 error: 75: type mismatch: '/' cannot operate on 'uint', 'int'
-48 errors
+50 errors

tests/sksl/errors/Ossfuzz27650.glsl

@@ -1,4 +1,5 @@
 ### Compilation failed:
 
 error: 1: expected 'int', but found 'float'
-1 error
+error: 1: unknown identifier 'i'
+2 errors

tests/sksl/errors/Ossfuzz28050.glsl

@@ -1,5 +1,4 @@
 ### Compilation failed:
 
 error: 2: invalid arguments to 'float[1]' constructor (expected 1 elements, but found 0)
-error: 3: function 'void wna()' is not defined
+1 error
-2 errors

tests/sksl/errors/Ossfuzz29444.glsl

@@ -1,5 +1,4 @@
 ### Compilation failed:
 
 error: 2: invalid arguments to 'float[1]' constructor (expected 1 elements, but found 0)
-error: 3: function 'void wna()' is not defined
+1 error
-2 errors

tests/sksl/runtime_errors/IllegalStatements.skvm

@@ -4,4 +4,5 @@ error: 3: discard statement is only permitted in fragment shaders
 error: 5: do-while loops are not supported
 error: 7: while loops are not supported
 error: 9: switch statements are not supported
-4 errors
+error: 9: function 'switch_stmt' can exit without returning a value
+5 errors