[CFE] Preserve file URIs of expressions in unevaluated constants.

This fixes missing positions on error messages from dart2js arising
from errors in constants in connection with environment constants.

Change-Id: Icc0666b82d0f28add053fbc231d680c6fdeeeff1
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/114603
Reviewed-by: Johnni Winther <johnniwinther@google.com>
Commit-Queue: Aske Simon Christensen <askesc@google.com>

pkg/front_end/lib/src/fasta/kernel/constant_evaluator.dart

@@ -592,8 +592,12 @@ class ConstantEvaluator extends RecursiveVisitor<Constant> {
     lazyDepth = 0;
     try {
       Constant result = _evaluateSubexpression(node);
-      if (errorOnUnevaluatedConstant && result is UnevaluatedConstant) {
-        return report(node, messageConstEvalUnevaluated);
+      if (result is UnevaluatedConstant) {
+        if (errorOnUnevaluatedConstant) {
+          return report(node, messageConstEvalUnevaluated);
+        }
+        return new UnevaluatedConstant(
+            removeRedundantFileUriExpressions(result.expression));
       }
       return result;
     } on _AbortDueToError catch (e) {
@@ -623,13 +627,8 @@ class ConstantEvaluator extends RecursiveVisitor<Constant> {
       }
       return new UnevaluatedConstant(new InvalidExpression(e.message.message));
     } on _AbortDueToInvalidExpression catch (e) {
-      // TODO(askesc): Copy position from erroneous node.
-      // Currently not possible, as it might be in a different file.
-      // Can be done if we add an explicit URI to InvalidExpression.
-      InvalidExpression invalid = new InvalidExpression(e.message);
-      if (invalid.fileOffset == TreeNode.noOffset) {
-        invalid.fileOffset = node.fileOffset;
-      }
+      InvalidExpression invalid = new InvalidExpression(e.message)
+        ..fileOffset = node.fileOffset;
       errorReporter.reportInvalidExpression(invalid);
       return new UnevaluatedConstant(invalid);
     }
@@ -649,8 +648,13 @@ class ConstantEvaluator extends RecursiveVisitor<Constant> {
   /// Produce an unevaluated constant node for an expression.
   Constant unevaluated(Expression original, Expression replacement) {
     replacement.fileOffset = original.fileOffset;
-    // TODO(askesc,johnniwinther): Preserve fileUri on [replacement].
-    return new UnevaluatedConstant(replacement);
+    return new UnevaluatedConstant(
+        new FileUriExpression(replacement, getFileUri(original))
+          ..fileOffset = original.fileOffset);
+  }
+
+  Expression removeRedundantFileUriExpressions(Expression node) {
+    return node.accept(new RedundantFileUriExpressionRemover()) as Expression;
   }
 
   /// Extract an expression from a (possibly unevaluated) constant to become
@@ -774,6 +778,11 @@ class ConstantEvaluator extends RecursiveVisitor<Constant> {
         node, 'Constant evaluation has no support for ${node.runtimeType}!');
   }
 
+  @override
+  Constant visitFileUriExpression(FileUriExpression node) {
+    return _evaluateSubexpression(node.expression);
+  }
+
   @override
   Constant visitNullLiteral(NullLiteral node) => nullConstant;
 
@@ -2312,6 +2321,23 @@ class EvaluationEnvironment {
   }
 }
 
+class RedundantFileUriExpressionRemover extends Transformer {
+  Uri currentFileUri = null;
+
+  TreeNode visitFileUriExpression(FileUriExpression node) {
+    if (node.fileUri == currentFileUri) {
+      return node.expression.accept(this);
+    } else {
+      Uri oldFileUri = currentFileUri;
+      currentFileUri = node.fileUri;
+      node.expression = node.expression.accept(this) as Expression
+        ..parent = node;
+      currentFileUri = oldFileUri;
+      return node;
+    }
+  }
+}
+
 // Used as control-flow to abort the current evaluation.
 class _AbortDueToError {
   final TreeNode node;

pkg/front_end/test/spell_checking_list_code.txt

@@ -666,6 +666,7 @@ relaxes
 remapped
 remedy
 removal
+remover
 reparse
 replacer
 replaces

pkg/kernel/lib/ast.dart

@@ -2442,6 +2442,9 @@ abstract class Expression extends TreeNode {
 /// An expression containing compile-time errors.
 ///
 /// Should throw a runtime error when evaluated.
+///
+/// The [fileOffset] of an [InvalidExpression] indicates the location in the
+/// tree where the expression occurs, rather than the location of the error.
 class InvalidExpression extends Expression {
   String message;