Make "config" accept a computed target

... and thus allowing the "business logic" in the configuration
target (e.g., setting defaults and derived options) to be shared
by many targets.

5 files changed, 122 insertions, 5 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index d50058f2..9b5b9846 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,7 @@ Initial stable release.
 
 ### Important changes since `1.0.0~beta5`
 
+- The "configure" built-in rule now evaluates "target"
 - Option `--dump-vars` added to `just analyse`
 - Rule fixes in propagating `ENV`
 - Launcher functionality added to `just-mr`
diff --git a/doc/concepts/built-in-rules.org b/doc/concepts/built-in-rules.org
index 0da0297f..28784193 100644
--- a/doc/concepts/built-in-rules.org
+++ b/doc/concepts/built-in-rules.org
@@ -125,10 +125,11 @@ map is empty.
 
 ** ~"configure"~
 
-The ~"configure"~ rule allows to configure a target with a given configuration.
-Similar to the ~"export"~ rule, the field ~"target"~ must name a single target
-(not a list). The ~"config"~ field is evaluated and must result in a map, which
-is used as configuration for the given target.
+The ~"configure"~ rule allows to configure a target with a given
+configuration. The field ~"target"~ is evaluated and the result
+of the evaluation must name a single target (not a list). The
+~"config"~ field is evaluated and must result in a map, which is
+used as configuration for the given target.
 
 This rule uses the given configuration to overlay the current environment for
 evaluating the given target, and thereby performs a configuration transition. It
diff --git a/src/buildtool/build_engine/target_map/built_in_rules.cpp b/src/buildtool/build_engine/target_map/built_in_rules.cpp
index a34dfb03..763385e2 100644
--- a/src/buildtool/build_engine/target_map/built_in_rules.cpp
+++ b/src/buildtool/build_engine/target_map/built_in_rules.cpp
@@ -953,7 +953,16 @@ void ConfigureRule(
     }
     auto param_config = key.config.Prune(*param_vars);
 
-    auto configured_target_name = desc->ReadExpression("target");
+    auto configured_target_name_exp = desc->ReadExpression("target");
+    if (not configured_target_name_exp) {
+        return;
+    }
+    auto configured_target_name = configured_target_name_exp.Evaluate(
+        param_config, {}, [logger](std::string const& msg) {
+            (*logger)(
+                fmt::format("Evaluating 'target' failed with error:\n{}", msg),
+                true);
+        });
     if (not configured_target_name) {
         return;
     }
diff --git a/test/end-to-end/targets/TARGETS b/test/end-to-end/targets/TARGETS
index 08b48284..31f4f900 100644
--- a/test/end-to-end/targets/TARGETS
+++ b/test/end-to-end/targets/TARGETS
@@ -22,6 +22,12 @@
   , "test": ["glob.sh"]
   , "deps": [["test/end-to-end", "tool-under-test"]]
   }
+, "configure target name":
+  { "type": ["@", "rules", "shell/test", "script"]
+  , "name": ["configure-target"]
+  , "test": ["configure-target.sh"]
+  , "deps": [["test/end-to-end", "tool-under-test"]]
+  }
 , "TESTS":
   { "type": "install"
   , "tainted": ["test"]
@@ -30,6 +36,7 @@
     , "repository naming"
     , "resolution of built-in rules"
     , "glob expansion"
+    , "configure target name"
     ]
   }
 }
diff --git a/test/end-to-end/targets/configure-target.sh b/test/end-to-end/targets/configure-target.sh
new file mode 100644
index 00000000..7c4dd9fd
--- /dev/null
+++ b/test/end-to-end/targets/configure-target.sh
@@ -0,0 +1,99 @@
+#!/bin/sh
+# Copyright 2022 Huawei Cloud Computing Technology Co., Ltd.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+set -e
+
+TOOL=$(realpath ./bin/tool-under-test)
+mkdir -p .root
+BUILDROOT=$(realpath .root)
+mkdir -p out
+OUTDIR=$(realpath out)
+
+mkdir src
+cd src
+touch ROOT
+cat > TARGETS <<'EOI'
+{ "configured":
+  { "type": "configure"
+  , "arguments_config": ["TARGET", "FOO", "BAR"]
+  , "target": {"type": "var", "name": "TARGET"}
+  , "config":
+    { "type": "let*"
+    , "bindings":
+      [ ["FOO", {"type": "var", "name": "FOO", "default": "foo"}]
+      , ["BAR", {"type": "var", "name": "BAR", "default": "bar"}]
+      , [ "FOOBAR"
+        , { "type": "join"
+          , "$1":
+            [{"type": "var", "name": "FOO"}, {"type": "var", "name": "BAR"}]
+          }
+        ]
+      ]
+    , "body": {"type": "env", "vars": ["FOO", "BAR", "FOOBAR"]}
+    }
+  }
+, "foobar":
+  { "type": "generic"
+  , "outs": ["out.txt"]
+  , "arguments_config": ["FOOBAR"]
+  , "cmds":
+    [ { "type": "join"
+      , "separator": " "
+      , "$1":
+        [ "echo"
+        , "-n"
+        , {"type": "join_cmd", "$1": [{"type": "var", "name": "FOOBAR"}]}
+        , "> out.txt"
+        ]
+      }
+    ]
+  }
+, "bar":
+  { "type": "file_gen"
+  , "arguments_config": ["BAR"]
+  , "name": "out.txt"
+  , "data": {"type": "var", "name": "BAR"}
+  }
+}
+EOI
+echo -n unrelated > out.txt
+
+
+echo
+${TOOL} install --local-build-root "${BUILDROOT}" -o "${OUTDIR}" \
+        -D '{"TARGET": "foobar", "FOO": "_F_O_O_"}' configured 2>&1
+echo
+cat "${OUTDIR}/out.txt"
+echo
+[ $(cat "${OUTDIR}/out.txt") = "_F_O_O_bar" ]
+
+echo
+${TOOL} install --local-build-root "${BUILDROOT}" -o "${OUTDIR}" \
+        -D '{"TARGET": "bar", "FOO": "_F_O_O_"}' configured 2>&1
+echo
+cat "${OUTDIR}/out.txt"
+echo
+[ $(cat "${OUTDIR}/out.txt") = "bar" ]
+
+echo
+${TOOL} install --local-build-root "${BUILDROOT}" -o "${OUTDIR}" \
+        -D '{"TARGET": "out.txt", "FOO": "_F_O_O_"}' configured 2>&1
+echo
+cat "${OUTDIR}/out.txt"
+echo
+[ $(cat "${OUTDIR}/out.txt") = "unrelated" ]
+
+
+echo DONE