Improve config syntax errors (nextflow-io#6721)

Author: bentsherman

modules/nf-lang/src/main/java/nextflow/config/control/ConfigResolveVisitor.java

@@ -17,6 +17,7 @@
 
 import java.util.Collections;
 import java.util.List;
+import java.util.regex.Pattern;
 
 import nextflow.config.ast.ConfigAssignNode;
 import nextflow.config.ast.ConfigIncludeNode;
@@ -78,6 +79,8 @@ public void visitConfigInclude(ConfigIncludeNode node) {
 
     private class DynamicVariablesVisitor extends ConfigVisitorSupport {
 
+        private static final Pattern ENV_VAR_NAME = Pattern.compile("[A-Z_]+[A-Z0-9_]*");
+
         @Override
         protected SourceUnit getSourceUnit() {
             return sourceUnit;
@@ -86,8 +89,12 @@ protected SourceUnit getSourceUnit() {
         @Override
         public void visitVariableExpression(VariableExpression node) {
             var variable = node.getAccessedVariable();
-            if( variable instanceof DynamicVariable )
-                resolver.addError("`" + node.getName() + "` is not defined", node);
+            if( variable instanceof DynamicVariable ) {
+                var message = "`" + node.getName() + "` is not defined";
+                if( ENV_VAR_NAME.matcher(variable.getName()).matches() )
+                    message += " (hint: use `env('...')` to access environment variable)";
+                resolver.addError(message, node);
+            }
         }
     }
 

modules/nf-lang/src/main/java/nextflow/config/parser/ConfigAstBuilder.java

@@ -316,6 +316,7 @@ private ConfigStatement configSelector(ConfigSelectorContext ctx) {
         var target = configPrimary(ctx.target);
         var statements = ctx.configBlockStatement().stream()
             .map(this::configBlockStatement)
+            .filter(stmt -> stmt != null)
             .toList();
         return new ConfigBlockNode(kind, target, statements);
     }

modules/nf-lang/src/main/java/nextflow/script/parser/ScriptAstBuilder.java

@@ -232,7 +232,7 @@ private ModuleNode compilationUnit(CompilationUnitContext ctx) {
         if( hasDeclarations ) {
             for( var stmt : statements ) {
                 if( !(stmt instanceof InvalidDeclaration) )
-                    collectSyntaxError(new SyntaxException("Statements cannot be mixed with script declarations -- move statements into a process or workflow", stmt));
+                    collectSyntaxError(new SyntaxException("Statements cannot be mixed with script declarations -- move statements into a process, workflow, or function", stmt));
             }
         }
 

modules/nf-lang/src/test/groovy/nextflow/config/control/ConfigResolveTest.groovy

@@ -61,6 +61,18 @@ class ConfigResolveTest extends Specification {
         errors[0].getStartLine() == 1
         errors[0].getStartColumn() == 36
         errors[0].getOriginalMessage() == '`process` is not defined'
+
+        when:
+        errors = check(
+            '''\
+            process.clusterOptions = "--cpus $PROCESS_CPUS"
+            '''
+        )
+        then:
+        errors.size() == 1
+        errors[0].getStartLine() == 1
+        errors[0].getStartColumn() == 34
+        errors[0].getOriginalMessage() == "`PROCESS_CPUS` is not defined (hint: use `env('...')` to access environment variable)"
     }
 
     def 'should report an error for an invalid config include' () {

modules/nf-lang/src/test/groovy/nextflow/config/parser/ConfigAstBuilderTest.groovy

@@ -73,6 +73,27 @@ class ConfigAstBuilderTest extends Specification {
         errors[0].getStartColumn() == 1
         errors[0].getOriginalMessage() == "If statements cannot be mixed with config statements"
 
+        when:
+        errors = check(
+            '''\
+            process {
+                withName: 'HELLO' {
+                    if( true ) {
+                        cpus = 8
+                    }
+                    else {
+                        cpus = 4
+                    }
+                }
+            }
+            '''
+        )
+        then:
+        errors.size() == 1
+        errors[0].getStartLine() == 3
+        errors[0].getStartColumn() == 9
+        errors[0].getOriginalMessage() == "If statements cannot be mixed with config statements"
+
         when:
         errors = check(
             '''\