[core] Add warning for invalid text-font values

3 files changed, 155 insertions, 0 deletions

diff --git a/src/mbgl/style/parser.cpp b/src/mbgl/style/parser.cpp
index 52d788b3a1..b177f2159c 100644
--- a/src/mbgl/style/parser.cpp
+++ b/src/mbgl/style/parser.cpp
@@ -119,6 +119,9 @@ StyleParseResult Parser::parse(const std::string& json) {
         }
     }
 
+    // Call for side effect of logging warnings for invalid values.
+    fontStacks();
+
     return nullptr;
 }
 
@@ -286,6 +289,9 @@ std::vector<FontStack> Parser::fontStacks() const {
                     for (const auto& value : function.possibleOutputs()) {
                         if (value) {
                             result.insert(*value);
+                        } else {
+                            Log::Warning(Event::ParseStyle, "Layer '%s' has an invalid value for text-font and will not work offline. Output values must be contained as literals within the expression.", layer->getID().c_str());
+                            break;
                         }
                     }
                 }
diff --git a/test/fixtures/style_parser/text-font.info.json b/test/fixtures/style_parser/text-font.info.json
new file mode 100644
index 0000000000..0fb9658269
--- /dev/null
+++ b/test/fixtures/style_parser/text-font.info.json
@@ -0,0 +1,14 @@
+{
+  "default": {
+    "log": [
+      [1, "WARNING", "ParseStyle", "Layer 'invalid expression - get' has an invalid value for text-font and will not work offline. Output values must be contained as literals within the expression."],
+      [1, "WARNING", "ParseStyle", "Layer 'invalid expression - case' has an invalid value for text-font and will not work offline. Output values must be contained as literals within the expression."],
+      [1, "WARNING", "ParseStyle", "Layer 'invalid expression - match' has an invalid value for text-font and will not work offline. Output values must be contained as literals within the expression."],
+      [1, "WARNING", "ParseStyle", "Layer 'invalid expression - at' has an invalid value for text-font and will not work offline. Output values must be contained as literals within the expression."],
+      [1, "WARNING", "ParseStyle", "Layer 'invalid expression - coalesce' has an invalid value for text-font and will not work offline. Output values must be contained as literals within the expression."],
+      [1, "WARNING", "ParseStyle", "Layer 'invalid expression - step' has an invalid value for text-font and will not work offline. Output values must be contained as literals within the expression."],
+      [1, "WARNING", "ParseStyle", "Layer 'invalid expression - let/var' has an invalid value for text-font and will not work offline. Output values must be contained as literals within the expression."],
+      [1, "WARNING", "ParseStyle", "Layer 'invalid expression - identity function' has an invalid value for text-font and will not work offline. Output values must be contained as literals within the expression."]
+    ]
+  }
+}
diff --git a/test/fixtures/style_parser/text-font.style.json b/test/fixtures/style_parser/text-font.style.json
new file mode 100644
index 0000000000..215807ca81
--- /dev/null
+++ b/test/fixtures/style_parser/text-font.style.json
@@ -0,0 +1,135 @@
+{
+  "version": 8,
+  "glyphs": "https://example.com/{fontstack}/{range}",
+  "sources": {
+    "vector": {
+      "type": "vector",
+      "url": "mapbox://mapbox.mapbox-streets-v5"
+    }
+  },
+  "layers": [
+    {
+      "id": "minimum",
+      "type": "symbol",
+      "source": "vector",
+      "source-layer": "layer",
+      "layout": {
+        "text-font": ["Helvetica"],
+        "text-field": "{foo}"
+      }
+    },
+    {
+      "id": "valid expression - case",
+      "type": "symbol",
+      "source": "vector",
+      "source-layer": "layer",
+      "layout": {
+        "text-font": ["case", ["==", "a", ["string", ["get", "text-font"]]], ["literal", ["Arial"]], ["literal", ["Helvetica"]]],
+        "text-field": "{foo}"
+      }
+    },
+    {
+      "id": "valid expression - match",
+      "type": "symbol",
+      "source": "vector",
+      "source-layer": "layer",
+      "layout": {
+        "text-font": ["match", ["get", "text-font"], "a", ["literal", ["Arial"]], ["literal", ["Helvetica"]]],
+        "text-field": "{foo}"
+      }
+    },
+    {
+      "id": "valid expression - step",
+      "type": "symbol",
+      "source": "vector",
+      "source-layer": "layer",
+      "layout": {
+        "text-font": ["array", "string", ["step", ["get", "text-font"], ["literal", ["Arial"]], 0, ["literal", ["Helvetica"]]]],
+        "text-field": "{foo}"
+      }
+    },
+    {
+      "id": "invalid expression - get",
+      "type": "symbol",
+      "source": "vector",
+      "source-layer": "layer",
+      "layout": {
+        "text-font": ["array", "string", ["get", "text-font"]],
+        "text-field": "{foo}"
+      }
+    },
+    {
+      "id": "invalid expression - case",
+      "type": "symbol",
+      "source": "vector",
+      "source-layer": "layer",
+      "layout": {
+        "text-font": ["case", ["==", "a", ["string", ["get", "text-font"]]], ["array", "string", ["get", "text-font-a"]], ["literal", ["Helvetica"]]],
+        "text-field": "{foo}"
+      }
+    },
+    {
+      "id": "invalid expression - match",
+      "type": "symbol",
+      "source": "vector",
+      "source-layer": "layer",
+      "layout": {
+        "text-font": ["match", ["get", "text-font"], "a", ["array", "string", ["get", "text-font-a"]], ["literal", ["Helvetica"]]],
+        "text-field": "{foo}"
+      }
+    },
+    {
+      "id": "invalid expression - at",
+      "type": "symbol",
+      "source": "vector",
+      "source-layer": "layer",
+      "layout": {
+        "text-font": ["array", "string", ["at", 0, ["array", ["get", "text-font"]]]],
+        "text-field": "{foo}"
+      }
+    },
+    {
+      "id": "invalid expression - coalesce",
+      "type": "symbol",
+      "source": "vector",
+      "source-layer": "layer",
+      "layout": {
+        "text-font": ["array", "string", ["coalesce", ["get", "text-font"]]],
+        "text-field": "{foo}"
+      }
+    },
+    {
+      "id": "invalid expression - step",
+      "type": "symbol",
+      "source": "vector",
+      "source-layer": "layer",
+      "layout": {
+        "text-font": ["step", ["zoom"], ["array", "string", ["get", "text-font-0"]], 0, ["array", "string", ["get", "text-font-1"]]],
+        "text-field": "{foo}"
+      }
+    },
+    {
+      "id": "invalid expression - let/var",
+      "type": "symbol",
+      "source": "vector",
+      "source-layer": "layer",
+      "layout": {
+        "text-font": ["let", "p", ["array", "string", ["get", "text-font"]], ["var", "p"]],
+        "text-field": "{foo}"
+      }
+    },
+    {
+      "id": "invalid expression - identity function",
+      "type": "symbol",
+      "source": "vector",
+      "source-layer": "layer",
+      "layout": {
+        "text-font": {
+          "type": "identity",
+          "property": "text-font"
+        },
+        "text-field": "{foo}"
+      }
+    }
+  ]
+}