From 2eaffa5cfb8ad8e5d18ac1ed61b4ae6b976852ee Mon Sep 17 00:00:00 2001
From: Klaus Aehlig <klaus.aehlig@huawei.com>
Date: Mon, 25 Mar 2024 11:57:42 +0100
Subject: Expression language: add float operations "*" and "+"

Numerical values are used at some places in justbuild: as value for
timeout scaling, as well as by the "range" expression that is used,
e.g., to define repreated test runs. Therefore, improve support
for numerical values by adding basic operations.
---
 doc/concepts/expressions.md                        |  8 ++++
 .../build_engine/expression/evaluator.cpp          | 38 +++++++++++++++++
 .../build_engine/expression/expression.test.cpp    | 48 ++++++++++++++++++++++
 3 files changed, 94 insertions(+)

diff --git a/doc/concepts/expressions.md b/doc/concepts/expressions.md
index dcd567af..192952f4 100644
--- a/doc/concepts/expressions.md
+++ b/doc/concepts/expressions.md
@@ -259,6 +259,14 @@ those) argument(s) to obtain the final result.
  - `"++"` The argument has to be a list of lists. The result is
    the concatenation of those lists.
 
+ - `"+"` The argument has to be a list of numbers. The result is
+   their sum (where the sum of the empty list is, of course, the
+   neutral element 0).
+
+ - `"*"` The argument has to be a list of numbers. The result
+   is their product (where the producut of the empty list is, of
+   course, the neutral element 1).
+
  - `"map_union"` The argument has to be a list of maps. The
    result is a map containing as keys the union of the keys of
    the maps in that list. For each key, the value is the value
diff --git a/src/buildtool/build_engine/expression/evaluator.cpp b/src/buildtool/build_engine/expression/evaluator.cpp
index d2cee809..4499552b 100644
--- a/src/buildtool/build_engine/expression/evaluator.cpp
+++ b/src/buildtool/build_engine/expression/evaluator.cpp
@@ -82,6 +82,42 @@ auto Flatten(ExpressionPtr const& expr) -> ExpressionPtr {
     return ExpressionPtr{result};
 }
 
+auto Addition(ExpressionPtr const& expr) -> ExpressionPtr {
+    if (not expr->IsList()) {
+        throw Evaluator::EvaluationError{fmt::format(
+            "Addition expects a list, but found: {}", expr->ToString())};
+    }
+    Expression::number_t result = 0.0;
+    auto const& list = expr->List();
+    std::for_each(list.begin(), list.end(), [&](auto const& f) {
+        if (not f->IsNumber()) {
+            throw Evaluator::EvaluationError{fmt::format(
+                "Non-number entry found for argument to addition: {}",
+                f->ToString())};
+        }
+        result += f->Number();
+    });
+    return ExpressionPtr(result);
+}
+
+auto Multiplication(ExpressionPtr const& expr) -> ExpressionPtr {
+    if (not expr->IsList()) {
+        throw Evaluator::EvaluationError{fmt::format(
+            "Multiplication expects a list, but found: {}", expr->ToString())};
+    }
+    Expression::number_t result = 1.0;
+    auto const& list = expr->List();
+    std::for_each(list.begin(), list.end(), [&](auto const& f) {
+        if (not f->IsNumber()) {
+            throw Evaluator::EvaluationError{fmt::format(
+                "Non-number entry found for argument to multiplication: {}",
+                f->ToString())};
+        }
+        result *= f->Number();
+    });
+    return ExpressionPtr(result);
+}
+
 auto All(ExpressionPtr const& list) -> ExpressionPtr {
     for (auto const& c : list->List()) {
         if (not ValueIsTrue(c)) {
@@ -954,6 +990,8 @@ auto const kBuiltInFunctions =
                           {"and", AndExpr},
                           {"or", OrExpr},
                           {"++", UnaryExpr(Flatten)},
+                          {"+", UnaryExpr(Addition)},
+                          {"*", UnaryExpr(Multiplication)},
                           {"nub_right", UnaryExpr(NubRight)},
                           {"range", UnaryExpr(Range)},
                           {"change_ending", ChangeEndingExpr},
diff --git a/test/buildtool/build_engine/expression/expression.test.cpp b/test/buildtool/build_engine/expression/expression.test.cpp
index 242c0f4a..83257bf8 100644
--- a/test/buildtool/build_engine/expression/expression.test.cpp
+++ b/test/buildtool/build_engine/expression/expression.test.cpp
@@ -744,6 +744,54 @@ TEST_CASE("Expression Evaluation", "[expression]") {  // NOLINT
         CHECK(result == Expression::FromJson(R"(["foo", "bar", "baz"])"_json));
     }
 
+    SECTION("+ expression") {
+        auto expr_empty = Expression::FromJson(R"(
+            { "type": "+"
+            , "$1": []
+            })"_json);
+        REQUIRE(expr_empty);
+
+        auto result_empty = expr_empty.Evaluate(env, fcts);
+        REQUIRE(result_empty);
+        REQUIRE(result_empty->IsNumber());
+        CHECK(result_empty == Expression::FromJson(R"(0.0)"_json));
+
+        auto expr = Expression::FromJson(R"(
+            { "type": "+"
+            , "$1": [2, 3, 7, -1]
+            })"_json);
+        REQUIRE(expr);
+
+        auto result = expr.Evaluate(env, fcts);
+        REQUIRE(result);
+        REQUIRE(result->IsNumber());
+        CHECK(result == Expression::FromJson(R"(11.0)"_json));
+    }
+
+    SECTION("* expression") {
+        auto expr_empty = Expression::FromJson(R"(
+            { "type": "*"
+            , "$1": []
+            })"_json);
+        REQUIRE(expr_empty);
+
+        auto result_empty = expr_empty.Evaluate(env, fcts);
+        REQUIRE(result_empty);
+        REQUIRE(result_empty->IsNumber());
+        CHECK(result_empty == Expression::FromJson(R"(1.0)"_json));
+
+        auto expr = Expression::FromJson(R"(
+            { "type": "*"
+            , "$1": [2, 3, 7, -1]
+            })"_json);
+        REQUIRE(expr);
+
+        auto result = expr.Evaluate(env, fcts);
+        REQUIRE(result);
+        REQUIRE(result->IsNumber());
+        CHECK(result == Expression::FromJson(R"(-42.0)"_json));
+    }
+
     SECTION("nub_right expression") {
         auto expr = Expression::FromJson(R"(
              {"type": "nub_right"
-- 
cgit v1.2.3